Writing an Abstract for Your Research Paper
![](http://cintadecorrer.fun/777/templates/cheerup1/res/banner1.gif)
Definition and Purpose of Abstracts
An abstract is a short summary of your (published or unpublished) research paper, usually about a paragraph (c. 6-7 sentences, 150-250 words) long. A well-written abstract serves multiple purposes:
- an abstract lets readers get the gist or essence of your paper or article quickly, in order to decide whether to read the full paper;
- an abstract prepares readers to follow the detailed information, analyses, and arguments in your full paper;
- and, later, an abstract helps readers remember key points from your paper.
It’s also worth remembering that search engines and bibliographic databases use abstracts, as well as the title, to identify key terms for indexing your published paper. So what you include in your abstract and in your title are crucial for helping other researchers find your paper or article.
If you are writing an abstract for a course paper, your professor may give you specific guidelines for what to include and how to organize your abstract. Similarly, academic journals often have specific requirements for abstracts. So in addition to following the advice on this page, you should be sure to look for and follow any guidelines from the course or journal you’re writing for.
The Contents of an Abstract
Abstracts contain most of the following kinds of information in brief form. The body of your paper will, of course, develop and explain these ideas much more fully. As you will see in the samples below, the proportion of your abstract that you devote to each kind of information—and the sequence of that information—will vary, depending on the nature and genre of the paper that you are summarizing in your abstract. And in some cases, some of this information is implied, rather than stated explicitly. The Publication Manual of the American Psychological Association , which is widely used in the social sciences, gives specific guidelines for what to include in the abstract for different kinds of papers—for empirical studies, literature reviews or meta-analyses, theoretical papers, methodological papers, and case studies.
Here are the typical kinds of information found in most abstracts:
- the context or background information for your research; the general topic under study; the specific topic of your research
- the central questions or statement of the problem your research addresses
- what’s already known about this question, what previous research has done or shown
- the main reason(s) , the exigency, the rationale , the goals for your research—Why is it important to address these questions? Are you, for example, examining a new topic? Why is that topic worth examining? Are you filling a gap in previous research? Applying new methods to take a fresh look at existing ideas or data? Resolving a dispute within the literature in your field? . . .
- your research and/or analytical methods
- your main findings , results , or arguments
- the significance or implications of your findings or arguments.
Your abstract should be intelligible on its own, without a reader’s having to read your entire paper. And in an abstract, you usually do not cite references—most of your abstract will describe what you have studied in your research and what you have found and what you argue in your paper. In the body of your paper, you will cite the specific literature that informs your research.
When to Write Your Abstract
Although you might be tempted to write your abstract first because it will appear as the very first part of your paper, it’s a good idea to wait to write your abstract until after you’ve drafted your full paper, so that you know what you’re summarizing.
What follows are some sample abstracts in published papers or articles, all written by faculty at UW-Madison who come from a variety of disciplines. We have annotated these samples to help you see the work that these authors are doing within their abstracts.
Choosing Verb Tenses within Your Abstract
The social science sample (Sample 1) below uses the present tense to describe general facts and interpretations that have been and are currently true, including the prevailing explanation for the social phenomenon under study. That abstract also uses the present tense to describe the methods, the findings, the arguments, and the implications of the findings from their new research study. The authors use the past tense to describe previous research.
The humanities sample (Sample 2) below uses the past tense to describe completed events in the past (the texts created in the pulp fiction industry in the 1970s and 80s) and uses the present tense to describe what is happening in those texts, to explain the significance or meaning of those texts, and to describe the arguments presented in the article.
The science samples (Samples 3 and 4) below use the past tense to describe what previous research studies have done and the research the authors have conducted, the methods they have followed, and what they have found. In their rationale or justification for their research (what remains to be done), they use the present tense. They also use the present tense to introduce their study (in Sample 3, “Here we report . . .”) and to explain the significance of their study (In Sample 3, This reprogramming . . . “provides a scalable cell source for. . .”).
Sample Abstract 1
From the social sciences.
Reporting new findings about the reasons for increasing economic homogamy among spouses
Gonalons-Pons, Pilar, and Christine R. Schwartz. “Trends in Economic Homogamy: Changes in Assortative Mating or the Division of Labor in Marriage?” Demography , vol. 54, no. 3, 2017, pp. 985-1005.
![analyze the sample abstract of the research paper below “The growing economic resemblance of spouses has contributed to rising inequality by increasing the number of couples in which there are two high- or two low-earning partners. [Annotation for the previous sentence: The first sentence introduces the topic under study (the “economic resemblance of spouses”). This sentence also implies the question underlying this research study: what are the various causes—and the interrelationships among them—for this trend?] The dominant explanation for this trend is increased assortative mating. Previous research has primarily relied on cross-sectional data and thus has been unable to disentangle changes in assortative mating from changes in the division of spouses’ paid labor—a potentially key mechanism given the dramatic rise in wives’ labor supply. [Annotation for the previous two sentences: These next two sentences explain what previous research has demonstrated. By pointing out the limitations in the methods that were used in previous studies, they also provide a rationale for new research.] We use data from the Panel Study of Income Dynamics (PSID) to decompose the increase in the correlation between spouses’ earnings and its contribution to inequality between 1970 and 2013 into parts due to (a) changes in assortative mating, and (b) changes in the division of paid labor. [Annotation for the previous sentence: The data, research and analytical methods used in this new study.] Contrary to what has often been assumed, the rise of economic homogamy and its contribution to inequality is largely attributable to changes in the division of paid labor rather than changes in sorting on earnings or earnings potential. Our findings indicate that the rise of economic homogamy cannot be explained by hypotheses centered on meeting and matching opportunities, and they show where in this process inequality is generated and where it is not.” (p. 985) [Annotation for the previous two sentences: The major findings from and implications and significance of this study.]](https://writing.wisc.edu/wp-content/uploads/sites/535/2019/08/Abstract-1.png)
Sample Abstract 2
From the humanities.
Analyzing underground pulp fiction publications in Tanzania, this article makes an argument about the cultural significance of those publications
Emily Callaci. “Street Textuality: Socialism, Masculinity, and Urban Belonging in Tanzania’s Pulp Fiction Publishing Industry, 1975-1985.” Comparative Studies in Society and History , vol. 59, no. 1, 2017, pp. 183-210.
![analyze the sample abstract of the research paper below “From the mid-1970s through the mid-1980s, a network of young urban migrant men created an underground pulp fiction publishing industry in the city of Dar es Salaam. [Annotation for the previous sentence: The first sentence introduces the context for this research and announces the topic under study.] As texts that were produced in the underground economy of a city whose trajectory was increasingly charted outside of formalized planning and investment, these novellas reveal more than their narrative content alone. These texts were active components in the urban social worlds of the young men who produced them. They reveal a mode of urbanism otherwise obscured by narratives of decolonization, in which urban belonging was constituted less by national citizenship than by the construction of social networks, economic connections, and the crafting of reputations. This article argues that pulp fiction novellas of socialist era Dar es Salaam are artifacts of emergent forms of male sociability and mobility. In printing fictional stories about urban life on pilfered paper and ink, and distributing their texts through informal channels, these writers not only described urban communities, reputations, and networks, but also actually created them.” (p. 210) [Annotation for the previous sentences: The remaining sentences in this abstract interweave other essential information for an abstract for this article. The implied research questions: What do these texts mean? What is their historical and cultural significance, produced at this time, in this location, by these authors? The argument and the significance of this analysis in microcosm: these texts “reveal a mode or urbanism otherwise obscured . . .”; and “This article argues that pulp fiction novellas. . . .” This section also implies what previous historical research has obscured. And through the details in its argumentative claims, this section of the abstract implies the kinds of methods the author has used to interpret the novellas and the concepts under study (e.g., male sociability and mobility, urban communities, reputations, network. . . ).]](https://writing.wisc.edu/wp-content/uploads/sites/535/2019/08/Abstract-2.png)
Sample Abstract/Summary 3
From the sciences.
Reporting a new method for reprogramming adult mouse fibroblasts into induced cardiac progenitor cells
Lalit, Pratik A., Max R. Salick, Daryl O. Nelson, Jayne M. Squirrell, Christina M. Shafer, Neel G. Patel, Imaan Saeed, Eric G. Schmuck, Yogananda S. Markandeya, Rachel Wong, Martin R. Lea, Kevin W. Eliceiri, Timothy A. Hacker, Wendy C. Crone, Michael Kyba, Daniel J. Garry, Ron Stewart, James A. Thomson, Karen M. Downs, Gary E. Lyons, and Timothy J. Kamp. “Lineage Reprogramming of Fibroblasts into Proliferative Induced Cardiac Progenitor Cells by Defined Factors.” Cell Stem Cell , vol. 18, 2016, pp. 354-367.
![analyze the sample abstract of the research paper below “Several studies have reported reprogramming of fibroblasts into induced cardiomyocytes; however, reprogramming into proliferative induced cardiac progenitor cells (iCPCs) remains to be accomplished. [Annotation for the previous sentence: The first sentence announces the topic under study, summarizes what’s already known or been accomplished in previous research, and signals the rationale and goals are for the new research and the problem that the new research solves: How can researchers reprogram fibroblasts into iCPCs?] Here we report that a combination of 11 or 5 cardiac factors along with canonical Wnt and JAK/STAT signaling reprogrammed adult mouse cardiac, lung, and tail tip fibroblasts into iCPCs. The iCPCs were cardiac mesoderm-restricted progenitors that could be expanded extensively while maintaining multipo-tency to differentiate into cardiomyocytes, smooth muscle cells, and endothelial cells in vitro. Moreover, iCPCs injected into the cardiac crescent of mouse embryos differentiated into cardiomyocytes. iCPCs transplanted into the post-myocardial infarction mouse heart improved survival and differentiated into cardiomyocytes, smooth muscle cells, and endothelial cells. [Annotation for the previous four sentences: The methods the researchers developed to achieve their goal and a description of the results.] Lineage reprogramming of adult somatic cells into iCPCs provides a scalable cell source for drug discovery, disease modeling, and cardiac regenerative therapy.” (p. 354) [Annotation for the previous sentence: The significance or implications—for drug discovery, disease modeling, and therapy—of this reprogramming of adult somatic cells into iCPCs.]](https://writing.wisc.edu/wp-content/uploads/sites/535/2019/08/Abstract-3.png)
Sample Abstract 4, a Structured Abstract
Reporting results about the effectiveness of antibiotic therapy in managing acute bacterial sinusitis, from a rigorously controlled study
Note: This journal requires authors to organize their abstract into four specific sections, with strict word limits. Because the headings for this structured abstract are self-explanatory, we have chosen not to add annotations to this sample abstract.
Wald, Ellen R., David Nash, and Jens Eickhoff. “Effectiveness of Amoxicillin/Clavulanate Potassium in the Treatment of Acute Bacterial Sinusitis in Children.” Pediatrics , vol. 124, no. 1, 2009, pp. 9-15.
“OBJECTIVE: The role of antibiotic therapy in managing acute bacterial sinusitis (ABS) in children is controversial. The purpose of this study was to determine the effectiveness of high-dose amoxicillin/potassium clavulanate in the treatment of children diagnosed with ABS.
METHODS : This was a randomized, double-blind, placebo-controlled study. Children 1 to 10 years of age with a clinical presentation compatible with ABS were eligible for participation. Patients were stratified according to age (<6 or ≥6 years) and clinical severity and randomly assigned to receive either amoxicillin (90 mg/kg) with potassium clavulanate (6.4 mg/kg) or placebo. A symptom survey was performed on days 0, 1, 2, 3, 5, 7, 10, 20, and 30. Patients were examined on day 14. Children’s conditions were rated as cured, improved, or failed according to scoring rules.
RESULTS: Two thousand one hundred thirty-five children with respiratory complaints were screened for enrollment; 139 (6.5%) had ABS. Fifty-eight patients were enrolled, and 56 were randomly assigned. The mean age was 6630 months. Fifty (89%) patients presented with persistent symptoms, and 6 (11%) presented with nonpersistent symptoms. In 24 (43%) children, the illness was classified as mild, whereas in the remaining 32 (57%) children it was severe. Of the 28 children who received the antibiotic, 14 (50%) were cured, 4 (14%) were improved, 4(14%) experienced treatment failure, and 6 (21%) withdrew. Of the 28children who received placebo, 4 (14%) were cured, 5 (18%) improved, and 19 (68%) experienced treatment failure. Children receiving the antibiotic were more likely to be cured (50% vs 14%) and less likely to have treatment failure (14% vs 68%) than children receiving the placebo.
CONCLUSIONS : ABS is a common complication of viral upper respiratory infections. Amoxicillin/potassium clavulanate results in significantly more cures and fewer failures than placebo, according to parental report of time to resolution.” (9)
Some Excellent Advice about Writing Abstracts for Basic Science Research Papers, by Professor Adriano Aguzzi from the Institute of Neuropathology at the University of Zurich:
![analyze the sample abstract of the research paper below](https://writing.wisc.edu/wp-content/uploads/sites/535/2018/07/Screen-Shot-2019-08-06-at-6.26.02-PM-e1565383158628.png)
Academic and Professional Writing
This is an accordion element with a series of buttons that open and close related content panels.
Analysis Papers
Reading Poetry
A Short Guide to Close Reading for Literary Analysis
Using Literary Quotations
Play Reviews
Writing a Rhetorical Précis to Analyze Nonfiction Texts
Incorporating Interview Data
Grant Proposals
Planning and Writing a Grant Proposal: The Basics
Additional Resources for Grants and Proposal Writing
Job Materials and Application Essays
Writing Personal Statements for Ph.D. Programs
- Before you begin: useful tips for writing your essay
- Guided brainstorming exercises
- Get more help with your essay
- Frequently Asked Questions
Resume Writing Tips
CV Writing Tips
Cover Letters
Business Letters
Proposals and Dissertations
Resources for Proposal Writers
Resources for Dissertators
Research Papers
Planning and Writing Research Papers
Quoting and Paraphrasing
Writing Annotated Bibliographies
Creating Poster Presentations
Thank-You Notes
Advice for Students Writing Thank-You Notes to Donors
Reading for a Review
Critical Reviews
Writing a Review of Literature
Scientific Reports
Scientific Report Format
Sample Lab Assignment
Writing for the Web
Writing an Effective Blog Post
Writing for Social Media: A Guide for Academics
Generate accurate APA citations for free
- Knowledge Base
- APA Style 7th edition
- How to write and format an APA abstract
APA Abstract (2020) | Formatting, Length, and Keywords
Published on November 6, 2020 by Raimo Streefkerk . Revised on January 17, 2024.
An APA abstract is a comprehensive summary of your paper in which you briefly address the research problem , hypotheses , methods , results , and implications of your research. It’s placed on a separate page right after the title page and is usually no longer than 250 words.
Most professional papers that are submitted for publication require an abstract. Student papers typically don’t need an abstract, unless instructed otherwise.
Instantly correct all language mistakes in your text
Upload your document to correct all your mistakes in minutes
![analyze the sample abstract of the research paper below upload-your-document-ai-proofreader](https://www.scribbr.com/wp-content/uploads/2024/01/grammar-check.webp)
Table of contents
How to format the abstract, how to write an apa abstract, which keywords to use, frequently asked questions, apa abstract example.
![analyze the sample abstract of the research paper below APA abstract (7th edition)](https://www.scribbr.com/wp-content/uploads/2020/11/abstract-apa-7th-ed.png)
Formatting instructions
Follow these five steps to format your abstract in APA Style:
- Insert a running head (for a professional paper—not needed for a student paper) and page number.
- Set page margins to 1 inch (2.54 cm).
- Write “Abstract” (bold and centered) at the top of the page.
- Do not indent the first line.
- Double-space the text.
- Use a legible font like Times New Roman (12 pt.).
- Limit the length to 250 words.
- Indent the first line 0.5 inches.
- Write the label “Keywords:” (italicized).
- Write keywords in lowercase letters.
- Separate keywords with commas.
- Do not use a period after the keywords.
Are your APA in-text citations flawless?
The AI-powered APA Citation Checker points out every error, tells you exactly what’s wrong, and explains how to fix it. Say goodbye to losing marks on your assignment!
Get started!
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://www.scribbr.com/wp-content/uploads/2020/11/citation-checker-issue-example-1.png)
The abstract is a self-contained piece of text that informs the reader what your research is about. It’s best to write the abstract after you’re finished with the rest of your paper.
The questions below may help structure your abstract. Try answering them in one to three sentences each.
- What is the problem? Outline the objective, research questions , and/or hypotheses .
- What has been done? Explain your research methods .
- What did you discover? Summarize the key findings and conclusions .
- What do the findings mean? Summarize the discussion and recommendations .
Check out our guide on how to write an abstract for more guidance and an annotated example.
Guide: writing an abstract
At the end of the abstract, you may include a few keywords that will be used for indexing if your paper is published on a database. Listing your keywords will help other researchers find your work.
Choosing relevant keywords is essential. Try to identify keywords that address your topic, method, or population. APA recommends including three to five keywords.
An abstract is a concise summary of an academic text (such as a journal article or dissertation ). It serves two main purposes:
- To help potential readers determine the relevance of your paper for their own research.
- To communicate your key findings to those who don’t have time to read the whole paper.
Abstracts are often indexed along with keywords on academic databases, so they make your work more easily findable. Since the abstract is the first thing any reader sees, it’s important that it clearly and accurately summarizes the contents of your paper.
An APA abstract is around 150–250 words long. However, always check your target journal’s guidelines and don’t exceed the specified word count.
In an APA Style paper , the abstract is placed on a separate page after the title page (page 2).
Avoid citing sources in your abstract . There are two reasons for this:
- The abstract should focus on your original research, not on the work of others.
- The abstract should be self-contained and fully understandable without reference to other sources.
There are some circumstances where you might need to mention other sources in an abstract: for example, if your research responds directly to another study or focuses on the work of a single theorist. In general, though, don’t include citations unless absolutely necessary.
Cite this Scribbr article
If you want to cite this source, you can copy and paste the citation or click the “Cite this Scribbr article” button to automatically add the citation to our free Citation Generator.
Streefkerk, R. (2024, January 17). APA Abstract (2020) | Formatting, Length, and Keywords. Scribbr. Retrieved July 16, 2024, from https://www.scribbr.com/apa-style/apa-abstract/
Is this article helpful?
Raimo Streefkerk
Other students also liked, apa headings and subheadings, apa running head, apa title page (7th edition) | template for students & professionals, get unlimited documents corrected.
✔ Free APA citation check included ✔ Unlimited document corrections ✔ Specialized in correcting academic texts
- Features for Creative Writers
- Features for Work
- Features for Higher Education
- Features for Teachers
- Features for Non-Native Speakers
- Learn Blog Grammar Guide Community Events FAQ
- Grammar Guide
How to Write an Abstract (With Examples)
![analyze the sample abstract of the research paper below Sarah Oakley headshot](https://assets.prowritingaid.com/f/145420/800x800/acb368dace/sarah_oakley.jpeg/m/)
Sarah Oakley
![analyze the sample abstract of the research paper below how to write an abstract](https://assets.prowritingaid.com/f/145420/750x469/e5fa9a0d51/blog-title-how-to-write-an-abstract.png/m/)
Table of Contents
What is an abstract in a paper, how long should an abstract be, 5 steps for writing an abstract, examples of an abstract, how prowritingaid can help you write an abstract.
If you are writing a scientific research paper or a book proposal, you need to know how to write an abstract, which summarizes the contents of the paper or book.
When researchers are looking for peer-reviewed papers to use in their studies, the first place they will check is the abstract to see if it applies to their work. Therefore, your abstract is one of the most important parts of your entire paper.
In this article, we’ll explain what an abstract is, what it should include, and how to write one.
An abstract is a concise summary of the details within a report. Some abstracts give more details than others, but the main things you’ll be talking about are why you conducted the research, what you did, and what the results show.
When a reader is deciding whether to read your paper completely, they will first look at the abstract. You need to be concise in your abstract and give the reader the most important information so they can determine if they want to read the whole paper.
Remember that an abstract is the last thing you’ll want to write for the research paper because it directly references parts of the report. If you haven’t written the report, you won’t know what to include in your abstract.
If you are writing a paper for a journal or an assignment, the publication or academic institution might have specific formatting rules for how long your abstract should be. However, if they don’t, most abstracts are between 150 and 300 words long.
A short word count means your writing has to be precise and without filler words or phrases. Once you’ve written a first draft, you can always use an editing tool, such as ProWritingAid, to identify areas where you can reduce words and increase readability.
If your abstract is over the word limit, and you’ve edited it but still can’t figure out how to reduce it further, your abstract might include some things that aren’t needed. Here’s a list of three elements you can remove from your abstract:
Discussion : You don’t need to go into detail about the findings of your research because your reader will find your discussion within the paper.
Definition of terms : Your readers are interested the field you are writing about, so they are likely to understand the terms you are using. If not, they can always look them up. Your readers do not expect you to give a definition of terms in your abstract.
References and citations : You can mention there have been studies that support or have inspired your research, but you do not need to give details as the reader will find them in your bibliography.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://cdn.prowritingaid.com/website/2.5.56596/images/cms/blog/student.png)
Good writing = better grades
ProWritingAid will help you improve the style, strength, and clarity of all your assignments.
If you’ve never written an abstract before, and you’re wondering how to write an abstract, we’ve got some steps for you to follow. It’s best to start with planning your abstract, so we’ve outlined the details you need to include in your plan before you write.
Remember to consider your audience when you’re planning and writing your abstract. They are likely to skim read your abstract, so you want to be sure your abstract delivers all the information they’re expecting to see at key points.
1. What Should an Abstract Include?
Abstracts have a lot of information to cover in a short number of words, so it’s important to know what to include. There are three elements that need to be present in your abstract:
Your context is the background for where your research sits within your field of study. You should briefly mention any previous scientific papers or experiments that have led to your hypothesis and how research develops in those studies.
Your hypothesis is your prediction of what your study will show. As you are writing your abstract after you have conducted your research, you should still include your hypothesis in your abstract because it shows the motivation for your paper.
Throughout your abstract, you also need to include keywords and phrases that will help researchers to find your article in the databases they’re searching. Make sure the keywords are specific to your field of study and the subject you’re reporting on, otherwise your article might not reach the relevant audience.
2. Can You Use First Person in an Abstract?
You might think that first person is too informal for a research paper, but it’s not. Historically, writers of academic reports avoided writing in first person to uphold the formality standards of the time. However, first person is more accepted in research papers in modern times.
If you’re still unsure whether to write in first person for your abstract, refer to any style guide rules imposed by the journal you’re writing for or your teachers if you are writing an assignment.
3. Abstract Structure
Some scientific journals have strict rules on how to structure an abstract, so it’s best to check those first. If you don’t have any style rules to follow, try using the IMRaD structure, which stands for Introduction, Methodology, Results, and Discussion.
![analyze the sample abstract of the research paper below how to structure an abstract](https://assets.prowritingaid.com/f/145420/750x469/9dbbec9c51/blog-content-how-to-structure-an-astract.png/m/)
Following the IMRaD structure, start with an introduction. The amount of background information you should include depends on your specific research area. Adding a broad overview gives you less room to include other details. Remember to include your hypothesis in this section.
The next part of your abstract should cover your methodology. Try to include the following details if they apply to your study:
What type of research was conducted?
How were the test subjects sampled?
What were the sample sizes?
What was done to each group?
How long was the experiment?
How was data recorded and interpreted?
Following the methodology, include a sentence or two about the results, which is where your reader will determine if your research supports or contradicts their own investigations.
The results are also where most people will want to find out what your outcomes were, even if they are just mildly interested in your research area. You should be specific about all the details but as concise as possible.
The last few sentences are your conclusion. It needs to explain how your findings affect the context and whether your hypothesis was correct. Include the primary take-home message, additional findings of importance, and perspective. Also explain whether there is scope for further research into the subject of your report.
Your conclusion should be honest and give the reader the ultimate message that your research shows. Readers trust the conclusion, so make sure you’re not fabricating the results of your research. Some readers won’t read your entire paper, but this section will tell them if it’s worth them referencing it in their own study.
4. How to Start an Abstract
The first line of your abstract should give your reader the context of your report by providing background information. You can use this sentence to imply the motivation for your research.
You don’t need to use a hook phrase or device in your first sentence to grab the reader’s attention. Your reader will look to establish relevance quickly, so readability and clarity are more important than trying to persuade the reader to read on.
5. How to Format an Abstract
Most abstracts use the same formatting rules, which help the reader identify the abstract so they know where to look for it.
Here’s a list of formatting guidelines for writing an abstract:
Stick to one paragraph
Use block formatting with no indentation at the beginning
Put your abstract straight after the title and acknowledgements pages
Use present or past tense, not future tense
There are two primary types of abstract you could write for your paper—descriptive and informative.
An informative abstract is the most common, and they follow the structure mentioned previously. They are longer than descriptive abstracts because they cover more details.
Descriptive abstracts differ from informative abstracts, as they don’t include as much discussion or detail. The word count for a descriptive abstract is between 50 and 150 words.
Here is an example of an informative abstract:
A growing trend exists for authors to employ a more informal writing style that uses “we” in academic writing to acknowledge one’s stance and engagement. However, few studies have compared the ways in which the first-person pronoun “we” is used in the abstracts and conclusions of empirical papers. To address this lacuna in the literature, this study conducted a systematic corpus analysis of the use of “we” in the abstracts and conclusions of 400 articles collected from eight leading electrical and electronic (EE) engineering journals. The abstracts and conclusions were extracted to form two subcorpora, and an integrated framework was applied to analyze and seek to explain how we-clusters and we-collocations were employed. Results revealed whether authors’ use of first-person pronouns partially depends on a journal policy. The trend of using “we” showed that a yearly increase occurred in the frequency of “we” in EE journal papers, as well as the existence of three “we-use” types in the article conclusions and abstracts: exclusive, inclusive, and ambiguous. Other possible “we-use” alternatives such as “I” and other personal pronouns were used very rarely—if at all—in either section. These findings also suggest that the present tense was used more in article abstracts, but the present perfect tense was the most preferred tense in article conclusions. Both research and pedagogical implications are proffered and critically discussed.
Wang, S., Tseng, W.-T., & Johanson, R. (2021). To We or Not to We: Corpus-Based Research on First-Person Pronoun Use in Abstracts and Conclusions. SAGE Open, 11(2).
Here is an example of a descriptive abstract:
From the 1850s to the present, considerable criminological attention has focused on the development of theoretically-significant systems for classifying crime. This article reviews and attempts to evaluate a number of these efforts, and we conclude that further work on this basic task is needed. The latter part of the article explicates a conceptual foundation for a crime pattern classification system, and offers a preliminary taxonomy of crime.
Farr, K. A., & Gibbons, D. C. (1990). Observations on the Development of Crime Categories. International Journal of Offender Therapy and Comparative Criminology, 34(3), 223–237.
If you want to ensure your abstract is grammatically correct and easy to read, you can use ProWritingAid to edit it. The software integrates with Microsoft Word, Google Docs, and most web browsers, so you can make the most of it wherever you’re writing your paper.
![analyze the sample abstract of the research paper below academic document type](https://assets.prowritingaid.com/f/145420/810x637/70e2b8d7b0/blog-content-academic-document-type.png/m/)
Before you edit with ProWritingAid, make sure the suggestions you are seeing are relevant for your document by changing the document type to “Abstract” within the Academic writing style section.
You can use the Readability report to check your abstract for places to improve the clarity of your writing. Some suggestions might show you where to remove words, which is great if you’re over your word count.
We hope the five steps and examples we’ve provided help you write a great abstract for your research paper.
Get started with ProWritingAid
Drop us a line or let's stay in touch via :
- Privacy Policy
![analyze the sample abstract of the research paper below Research Method](https://researchmethod.net/wp-content/uploads/2022/07/logo.png)
Home » Research Paper Abstract – Writing Guide and Examples
Research Paper Abstract – Writing Guide and Examples
Table of Contents
![analyze the sample abstract of the research paper below Research Paper Abstract](https://researchmethod.net/wp-content/uploads/2023/04/Research_Paper_Abstract-1024x576.jpg)
Research Paper Abstract
Research Paper Abstract is a brief summary of a research pape r that describes the study’s purpose, methods, findings, and conclusions . It is often the first section of the paper that readers encounter, and its purpose is to provide a concise and accurate overview of the paper’s content. The typical length of an abstract is usually around 150-250 words, and it should be written in a concise and clear manner.
Research Paper Abstract Structure
The structure of a research paper abstract usually includes the following elements:
- Background or Introduction: Briefly describe the problem or research question that the study addresses.
- Methods : Explain the methodology used to conduct the study, including the participants, materials, and procedures.
- Results : Summarize the main findings of the study, including statistical analyses and key outcomes.
- Conclusions : Discuss the implications of the study’s findings and their significance for the field, as well as any limitations or future directions for research.
- Keywords : List a few keywords that describe the main topics or themes of the research.
How to Write Research Paper Abstract
Here are the steps to follow when writing a research paper abstract:
- Start by reading your paper: Before you write an abstract, you should have a complete understanding of your paper. Read through the paper carefully, making sure you understand the purpose, methods, results, and conclusions.
- Identify the key components : Identify the key components of your paper, such as the research question, methods used, results obtained, and conclusion reached.
- Write a draft: Write a draft of your abstract, using concise and clear language. Make sure to include all the important information, but keep it short and to the point. A good rule of thumb is to keep your abstract between 150-250 words.
- Use clear and concise language : Use clear and concise language to explain the purpose of your study, the methods used, the results obtained, and the conclusions drawn.
- Emphasize your findings: Emphasize your findings in the abstract, highlighting the key results and the significance of your study.
- Revise and edit: Once you have a draft, revise and edit it to ensure that it is clear, concise, and free from errors.
- Check the formatting: Finally, check the formatting of your abstract to make sure it meets the requirements of the journal or conference where you plan to submit it.
Research Paper Abstract Examples
Research Paper Abstract Examples could be following:
Title : “The Effectiveness of Cognitive-Behavioral Therapy for Treating Anxiety Disorders: A Meta-Analysis”
Abstract : This meta-analysis examines the effectiveness of cognitive-behavioral therapy (CBT) in treating anxiety disorders. Through the analysis of 20 randomized controlled trials, we found that CBT is a highly effective treatment for anxiety disorders, with large effect sizes across a range of anxiety disorders, including generalized anxiety disorder, panic disorder, and social anxiety disorder. Our findings support the use of CBT as a first-line treatment for anxiety disorders and highlight the importance of further research to identify the mechanisms underlying its effectiveness.
Title : “Exploring the Role of Parental Involvement in Children’s Education: A Qualitative Study”
Abstract : This qualitative study explores the role of parental involvement in children’s education. Through in-depth interviews with 20 parents of children in elementary school, we found that parental involvement takes many forms, including volunteering in the classroom, helping with homework, and communicating with teachers. We also found that parental involvement is influenced by a range of factors, including parent and child characteristics, school culture, and socio-economic status. Our findings suggest that schools and educators should prioritize building strong partnerships with parents to support children’s academic success.
Title : “The Impact of Exercise on Cognitive Function in Older Adults: A Systematic Review and Meta-Analysis”
Abstract : This paper presents a systematic review and meta-analysis of the existing literature on the impact of exercise on cognitive function in older adults. Through the analysis of 25 randomized controlled trials, we found that exercise is associated with significant improvements in cognitive function, particularly in the domains of executive function and attention. Our findings highlight the potential of exercise as a non-pharmacological intervention to support cognitive health in older adults.
When to Write Research Paper Abstract
The abstract of a research paper should typically be written after you have completed the main body of the paper. This is because the abstract is intended to provide a brief summary of the key points and findings of the research, and you can’t do that until you have completed the research and written about it in detail.
Once you have completed your research paper, you can begin writing your abstract. It is important to remember that the abstract should be a concise summary of your research paper, and should be written in a way that is easy to understand for readers who may not have expertise in your specific area of research.
Purpose of Research Paper Abstract
The purpose of a research paper abstract is to provide a concise summary of the key points and findings of a research paper. It is typically a brief paragraph or two that appears at the beginning of the paper, before the introduction, and is intended to give readers a quick overview of the paper’s content.
The abstract should include a brief statement of the research problem, the methods used to investigate the problem, the key results and findings, and the main conclusions and implications of the research. It should be written in a clear and concise manner, avoiding jargon and technical language, and should be understandable to a broad audience.
The abstract serves as a way to quickly and easily communicate the main points of a research paper to potential readers, such as academics, researchers, and students, who may be looking for information on a particular topic. It can also help researchers determine whether a paper is relevant to their own research interests and whether they should read the full paper.
About the author
Muhammad Hassan
Researcher, Academic Writer, Web developer
You may also like
![analyze the sample abstract of the research paper below Significance of the Study](https://researchmethod.net/wp-content/uploads/2023/04/Significance_of_the_Study-145x100.png)
Significance of the Study – Examples and Writing...
![analyze the sample abstract of the research paper below Research Contribution](https://researchmethod.net/wp-content/uploads/2023/04/Research_Contribution-145x100.png)
Research Contribution – Thesis Guide
![analyze the sample abstract of the research paper below Research Paper Introduction](https://researchmethod.net/wp-content/uploads/2023/04/Research_Paper_Introduction-145x100.png)
Research Paper Introduction – Writing Guide and...
![analyze the sample abstract of the research paper below Research Paper Title Page](https://researchmethod.net/wp-content/uploads/2023/04/Research_Paper_Title_Page-145x100.png)
Research Paper Title Page – Example and Making...
![analyze the sample abstract of the research paper below Research Paper Outline](https://researchmethod.net/wp-content/uploads/2023/04/Research_Paper_Outline-145x100.png)
Research Paper Outline – Types, Example, Template
![analyze the sample abstract of the research paper below Context of the Study](https://researchmethod.net/wp-content/uploads/2023/04/Context_of_the_Study-145x100.png)
Context of the Study – Writing Guide and Examples
How to craft an APA abstract
Last updated
16 December 2023
Reviewed by
An APA abstract is a brief but thorough summary of a scientific paper. It gives readers a clear overview of what the paper is about and what it intends to prove.
The purpose of an abstract is to allow researchers to quickly understand the paper's topic and purpose so they can decide whether it will be useful to them.
- What is the APA style?
APA style is a method of formatting and documentation used by the American Psychological Association. This style is used primarily for papers in the field of education and in the social sciences, including:
Anthropology
What is an abstract in APA format?
Writing an abstract in APA format requires you to conform to the writing rules for APA-style papers, including the following guidelines:
The abstract should be 150–250 words
It should be brief but concise, containing all the paper's main points
The abstract is a separate page that comes after the title page and before the paper's main content
- Key elements of an APA abstract
While the rules for constructing an APA abstract are straightforward, the process can be challenging. You need to pack a great deal of relevant content into a short piece.
The essential elements of an APA abstract are:
Running header containing the title of the paper and page number
Section label, centered and in bold, containing the word "abstract"
The main content of the abstract, 150–250 words in length and double-spaced
A list of keywords, indented and introduced with the word "keywords" in italics
Essential points to cover in an APA abstract
When you’re creating your APA abstract, consider the following questions.
What is the main topic the paper is addressing?
People searching for research on your topic will probably be browsing many papers and studies. The way your abstract is crafted will help to determine whether they feel your paper is worth reading.
Are your research methods quantitative or qualitative?
Quantitative research is focused on numbers and statistics, typically gathered from studies and polls where the questions are in yes/no or multiple-choice format.
Qualitative research is based on language and gathered using methods such as interviews and focus groups. It is more detailed and time-consuming to gather than quantitative research but can yield more complex and nuanced results.
Did you use primary or secondary sources?
Another key element is whether your research is based on primary or secondary sources.
Primary research is data that you or your research team gathered. Secondary research is gathered from existing sources, such as databases or previously published studies.
Is your research descriptive or experimental?
Your research may be descriptive, experimental, or both.
With descriptive research , you’re describing or analyzing existing studies or theories on the topic. You may be using surveys, case studies, or observation to study the topic.
Experimental research studies variables using the scientific method. With an experiment, your objective is to establish a cause-and-effect relationship between two variables (or show the lack of one).
What conclusion did you reach?
Readers will want to know upfront what your paper is claiming or proving. Your APA abstract should give them a condensed version of your conclusions. Summarize your most significant findings.
It's customary to place your findings and conclusion in the final sentence of the abstract. This should be directly related to the main topic of the paper.
What is the relevance of your findings?
Show readers that your paper is a significant contribution to the field. While staying accurate and not overstating your case, boast a bit about why people need to read your paper.
Briefly describe the implications and importance of your findings. You can also point out any further research that is needed concerning this topic.
Did you choose the most appropriate keywords?
Including keywords is useful for indexing if your paper is eventually included in a database. Choose keywords that are relevant to the paper and as specific as possible.
For example, if your paper is about signs of learning disabilities in elementary-age children, your keyword list might include:
Learning disability symptoms
Elementary education
Language-based learning disabilities
Any other terms discussed in the paper
- How to format an APA abstract
Use standard APA formatting with double spacing, 12pt Times New Roman font, and one-inch margins.
Place a running head at the top left-hand side of the page. This is an abbreviated version of the paper's title. Use all capital letters for the running header. This is not usually required for academic papers but is essential if you are submitting the paper for publication. The page number “2” should follow the running header (Page 1 is the title page).
Just under the running head, in the center, place the word "abstract."
Place your list of keywords at the end. The list should be indented and, according to APA guidelines, contain three to five keywords.
- What are the 3 types of abstracts?
There are certain variations in different types of APA abstracts. Here are three of the most common ones.
Experimental or lab report abstracts
An abstract for an experimental or lab report needs to communicate the key purpose and findings of the experiment. Include the following:
Purpose and importance of the experiment
Hypothesis of the experiment
Methods used to test the hypothesis
Summary of the results of the experiment, including whether you proved or rejected the hypothesis
Literature review abstracts
A literature review is a survey of published work on a work of literature. It may be part of a thesis, dissertation, or research paper .
The abstract for a literature review should contain:
A description of your purpose for covering the research topic
Your thesis statement
A description of the sources used in the review
Your conclusions based on the findings
Psychology lab reports
Psychology lab reports are part of the experiment report category. Psychology experiments, however, may contain distinctive elements.
Describe the goal or purpose of the experiment
If the experiment includes human subjects, describe them. Mention the number of participants and what demographic they fit
Describe any tools, equipment, or apparatus you used for the experiment. For example, some experiments use electroencephalography (EEG) to measure brain waves. You may have also used tools such as questionnaires , case studies , or naturalistic observation. Describe the procedure and parameters of the experiment.
Summarize your conclusions
- What not to include in an APA abstract
As this section is 250 words maximum, it's important to know what should not be included.
Avoid the following in an APA abstract:
Jargon, acronyms, or abbreviations
Citations. These should appear in the body of the paper.
Lengthy or secondary information. Keep it brief and stick to the main points. Readers should want to read your paper for more detailed information.
Opinions or subjective comments
Anything not covered in the paper
- Guidelines for writing an APA abstract
While an abstract is the shortest section of your paper, it is nevertheless one of the most important parts. It determines whether or not someone decides that the paper is worth reading or not. What follows are some guidelines to keep in mind when creating your APA abstract.
Focus on your main point. Don't try to fit in multiple conclusions. The idea is to give readers a clear idea of what your main point or conclusion is. On a similar note, be explicit about the implications and significance of your findings. This is what will motivate people to read your paper.
Write the abstract last. Ensure the abstract accurately conveys the content and conclusions of your paper. You may want to start with a rough draft of the abstract, which you can use as an outline to guide you when writing your paper. If you do this, make sure you edit and update the abstract after the full paper is complete.
Proofread your abstract. As the abstract is short and the first part of the paper people will read, it's especially important to make it clear and free of spelling, grammatical, or factual errors. Ask someone in your field to read through it.
Write the abstract for a general audience. While the paper may be aimed at academics, scientists, or specialists in your field, the abstract should be accessible to a broad audience. Minimize jargon and acronyms. This will make the paper easier to find by people looking for information on the topic.
Choose your keywords with care. The more relevant keywords you include, the more searchable your paper will be. Look up papers on comparable topics for guidance.
Follow any specific guidelines that apply to your paper. Requirements for the abstract may differ slightly depending on the topic or guidelines set by a particular instructor or publication.
APA style is commonly used in the fields of psychology, sociology, anthropology, economics, and education.
If you’re writing an abstract in APA style, there are certain conventions to follow. Your readers and people in your industry will expect you to adhere to particular elements of layout, content, and structure.
Follow our advice in this article, and you will be confident that your APA abstract complies with the expected standards and will encourage people to read your full paper.
Should you be using a customer insights hub?
Do you want to discover previous research faster?
Do you share your research findings with others?
Do you analyze research data?
Start for free today, add your research, and get to key insights faster
Editor’s picks
Last updated: 18 April 2023
Last updated: 27 February 2023
Last updated: 6 February 2023
Last updated: 6 October 2023
Last updated: 5 February 2023
Last updated: 16 April 2023
Last updated: 9 March 2023
Last updated: 12 December 2023
Last updated: 11 March 2024
Last updated: 4 July 2024
Last updated: 6 March 2024
Last updated: 5 March 2024
Last updated: 13 May 2024
Latest articles
Related topics, .css-je19u9{-webkit-align-items:flex-end;-webkit-box-align:flex-end;-ms-flex-align:flex-end;align-items:flex-end;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;-webkit-box-flex-wrap:wrap;-webkit-flex-wrap:wrap;-ms-flex-wrap:wrap;flex-wrap:wrap;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;row-gap:0;text-align:center;max-width:671px;}@media (max-width: 1079px){.css-je19u9{max-width:400px;}.css-je19u9>span{white-space:pre;}}@media (max-width: 799px){.css-je19u9{max-width:400px;}.css-je19u9>span{white-space:pre;}} decide what to .css-1kiodld{max-height:56px;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;}@media (max-width: 1079px){.css-1kiodld{display:none;}} build next, decide what to build next.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://images.ctfassets.net/mmu68mmhtb17/17ZYa6NHX7Cxs8IQ6qjsrJ/847a33e6669349a48c62f76bee8312ea/1.png?w=84&h=84&q=80&fm=png)
Users report unexpectedly high data usage, especially during streaming sessions.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://images.ctfassets.net/mmu68mmhtb17/2Shmch4SlrH6Jhpy8xX2lJ/a29b5842d6fe850fe34c7df6de5804d3/2.png?w=84&h=84&q=80&fm=png)
Users find it hard to navigate from the home page to relevant playlists in the app.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://images.ctfassets.net/mmu68mmhtb17/NBTArUW1okjZYDrAbCt6D/3bdbfae8f41fcbd5b24eb9997beda473/3.png?w=84&h=84&q=80&fm=png)
It would be great to have a sleep timer feature, especially for bedtime listening.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://images.ctfassets.net/mmu68mmhtb17/5gXUnpstdzPtrzGDMf4YAp/eafd05b570ddf2df2e9fb763800b0499/4.png?w=84&h=84&q=80&fm=png)
I need better filters to find the songs or artists I’m looking for.
- Essential points to cover in an APA abstract
Log in or sign up
Get started for free
When you choose to publish with PLOS, your research makes an impact. Make your work accessible to all, without restrictions, and accelerate scientific discovery with options like preprints and published peer review that make your work more Open.
- PLOS Biology
- PLOS Climate
- PLOS Complex Systems
- PLOS Computational Biology
- PLOS Digital Health
- PLOS Genetics
- PLOS Global Public Health
- PLOS Medicine
- PLOS Mental Health
- PLOS Neglected Tropical Diseases
- PLOS Pathogens
- PLOS Sustainability and Transformation
- PLOS Collections
- How to Write an Abstract
![analyze the sample abstract of the research paper below Abstract](https://plos.org/wp-content/uploads/2020/07/abstract-image_color-tone-1120x630.jpg)
Expedite peer review, increase search-ability, and set the tone for your study
The abstract is your chance to let your readers know what they can expect from your article. Learn how to write a clear, and concise abstract that will keep your audience reading.
How your abstract impacts editorial evaluation and future readership
After the title , the abstract is the second-most-read part of your article. A good abstract can help to expedite peer review and, if your article is accepted for publication, it’s an important tool for readers to find and evaluate your work. Editors use your abstract when they first assess your article. Prospective reviewers see it when they decide whether to accept an invitation to review. Once published, the abstract gets indexed in PubMed and Google Scholar , as well as library systems and other popular databases. Like the title, your abstract influences keyword search results. Readers will use it to decide whether to read the rest of your article. Other researchers will use it to evaluate your work for inclusion in systematic reviews and meta-analysis. It should be a concise standalone piece that accurately represents your research.
![analyze the sample abstract of the research paper below](https://plos.org/wp-content/uploads/2020/07/How-to-write-a-great-title-funnel_Abstract_1b.png)
What to include in an abstract
The main challenge you’ll face when writing your abstract is keeping it concise AND fitting in all the information you need. Depending on your subject area the journal may require a structured abstract following specific headings. A structured abstract helps your readers understand your study more easily. If your journal doesn’t require a structured abstract it’s still a good idea to follow a similar format, just present the abstract as one paragraph without headings.
Background or Introduction – What is currently known? Start with a brief, 2 or 3 sentence, introduction to the research area.
Objectives or Aims – What is the study and why did you do it? Clearly state the research question you’re trying to answer.
Methods – What did you do? Explain what you did and how you did it. Include important information about your methods, but avoid the low-level specifics. Some disciplines have specific requirements for abstract methods.
- CONSORT for randomized trials.
- STROBE for observational studies
- PRISMA for systematic reviews and meta-analyses
Results – What did you find? Briefly give the key findings of your study. Include key numeric data (including confidence intervals or p values), where possible.
Conclusions – What did you conclude? Tell the reader why your findings matter, and what this could mean for the ‘bigger picture’ of this area of research.
Writing tips
The main challenge you may find when writing your abstract is keeping it concise AND convering all the information you need to.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://plos.org/wp-content/uploads/2020/02/Thumb-up_GREEN-e1598388261821.png)
- Keep it concise and to the point. Most journals have a maximum word count, so check guidelines before you write the abstract to save time editing it later.
- Write for your audience. Are they specialists in your specific field? Are they cross-disciplinary? Are they non-specialists? If you’re writing for a general audience, or your research could be of interest to the public keep your language as straightforward as possible. If you’re writing in English, do remember that not all of your readers will necessarily be native English speakers.
- Focus on key results, conclusions and take home messages.
- Write your paper first, then create the abstract as a summary.
- Check the journal requirements before you write your abstract, eg. required subheadings.
- Include keywords or phrases to help readers search for your work in indexing databases like PubMed or Google Scholar.
- Double and triple check your abstract for spelling and grammar errors. These kind of errors can give potential reviewers the impression that your research isn’t sound, and can make it easier to find reviewers who accept the invitation to review your manuscript. Your abstract should be a taste of what is to come in the rest of your article.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://plos.org/wp-content/uploads/2020/05/Thumb-DOWN_RED-e1598388156186.png)
Don’t
- Sensationalize your research.
- Speculate about where this research might lead in the future.
- Use abbreviations or acronyms (unless absolutely necessary or unless they’re widely known, eg. DNA).
- Repeat yourself unnecessarily, eg. “Methods: We used X technique. Results: Using X technique, we found…”
- Contradict anything in the rest of your manuscript.
- Include content that isn’t also covered in the main manuscript.
- Include citations or references.
Tip: How to edit your work
Editing is challenging, especially if you are acting as both a writer and an editor. Read our guidelines for advice on how to refine your work, including useful tips for setting your intentions, re-review, and consultation with colleagues.
- How to Write a Great Title
- How to Write Your Methods
- How to Report Statistics
- How to Write Discussions and Conclusions
- How to Edit Your Work
The contents of the Peer Review Center are also available as a live, interactive training session, complete with slides, talking points, and activities. …
The contents of the Writing Center are also available as a live, interactive training session, complete with slides, talking points, and activities. …
There’s a lot to consider when deciding where to submit your work. Learn how to choose a journal that will help your study reach its audience, while reflecting your values as a researcher…
- Resources Home 🏠
- Try SciSpace Copilot
- Search research papers
- Add Copilot Extension
- Try AI Detector
- Try Paraphraser
- Try Citation Generator
- April Papers
- June Papers
- July Papers
![analyze the sample abstract of the research paper below SciSpace Resources](https://typeset.io/resources/content/images/2023/01/Scispace--600---72-px---1-.png)
Abstract Writing: A Step-by-Step Guide With Tips & Examples
Table of Contents
Introduction
Abstracts of research papers have always played an essential role in describing your research concisely and clearly to researchers and editors of journals, enticing them to continue reading. However, with the widespread availability of scientific databases, the need to write a convincing abstract is more crucial now than during the time of paper-bound manuscripts.
Abstracts serve to "sell" your research and can be compared with your "executive outline" of a resume or, rather, a formal summary of the critical aspects of your work. Also, it can be the "gist" of your study. Since most educational research is done online, it's a sign that you have a shorter time for impressing your readers, and have more competition from other abstracts that are available to be read.
The APCI (Academic Publishing and Conferences International) articulates 12 issues or points considered during the final approval process for conferences & journals and emphasises the importance of writing an abstract that checks all these boxes (12 points). Since it's the only opportunity you have to captivate your readers, you must invest time and effort in creating an abstract that accurately reflects the critical points of your research.
With that in mind, let’s head over to understand and discover the core concept and guidelines to create a substantial abstract. Also, learn how to organise the ideas or plots into an effective abstract that will be awe-inspiring to the readers you want to reach.
What is Abstract? Definition and Overview
The word "Abstract' is derived from Latin abstractus meaning "drawn off." This etymological meaning also applies to art movements as well as music, like abstract expressionism. In this context, it refers to the revealing of the artist's intention.
Based on this, you can determine the meaning of an abstract: A condensed research summary. It must be self-contained and independent of the body of the research. However, it should outline the subject, the strategies used to study the problem, and the methods implemented to attain the outcomes. The specific elements of the study differ based on the area of study; however, together, it must be a succinct summary of the entire research paper.
Abstracts are typically written at the end of the paper, even though it serves as a prologue. In general, the abstract must be in a position to:
- Describe the paper.
- Identify the problem or the issue at hand.
- Explain to the reader the research process, the results you came up with, and what conclusion you've reached using these results.
- Include keywords to guide your strategy and the content.
Furthermore, the abstract you submit should not reflect upon any of the following elements:
- Examine, analyse or defend the paper or your opinion.
- What you want to study, achieve or discover.
- Be redundant or irrelevant.
After reading an abstract, your audience should understand the reason - what the research was about in the first place, what the study has revealed and how it can be utilised or can be used to benefit others. You can understand the importance of abstract by knowing the fact that the abstract is the most frequently read portion of any research paper. In simpler terms, it should contain all the main points of the research paper.
What is the Purpose of an Abstract?
Abstracts are typically an essential requirement for research papers; however, it's not an obligation to preserve traditional reasons without any purpose. Abstracts allow readers to scan the text to determine whether it is relevant to their research or studies. The abstract allows other researchers to decide if your research paper can provide them with some additional information. A good abstract paves the interest of the audience to pore through your entire paper to find the content or context they're searching for.
Abstract writing is essential for indexing, as well. The Digital Repository of academic papers makes use of abstracts to index the entire content of academic research papers. Like meta descriptions in the regular Google outcomes, abstracts must include keywords that help researchers locate what they seek.
Types of Abstract
Informative and Descriptive are two kinds of abstracts often used in scientific writing.
A descriptive abstract gives readers an outline of the author's main points in their study. The reader can determine if they want to stick to the research work, based on their interest in the topic. An abstract that is descriptive is similar to the contents table of books, however, the format of an abstract depicts complete sentences encapsulated in one paragraph. It is unfortunate that the abstract can't be used as a substitute for reading a piece of writing because it's just an overview, which omits readers from getting an entire view. Also, it cannot be a way to fill in the gaps the reader may have after reading this kind of abstract since it does not contain crucial information needed to evaluate the article.
To conclude, a descriptive abstract is:
- A simple summary of the task, just summarises the work, but some researchers think it is much more of an outline
- Typically, the length is approximately 100 words. It is too short when compared to an informative abstract.
- A brief explanation but doesn't provide the reader with the complete information they need;
- An overview that omits conclusions and results
An informative abstract is a comprehensive outline of the research. There are times when people rely on the abstract as an information source. And the reason is why it is crucial to provide entire data of particular research. A well-written, informative abstract could be a good substitute for the remainder of the paper on its own.
A well-written abstract typically follows a particular style. The author begins by providing the identifying information, backed by citations and other identifiers of the papers. Then, the major elements are summarised to make the reader aware of the study. It is followed by the methodology and all-important findings from the study. The conclusion then presents study results and ends the abstract with a comprehensive summary.
In a nutshell, an informative abstract:
- Has a length that can vary, based on the subject, but is not longer than 300 words.
- Contains all the content-like methods and intentions
- Offers evidence and possible recommendations.
Informative Abstracts are more frequent than descriptive abstracts because of their extensive content and linkage to the topic specifically. You should select different types of abstracts to papers based on their length: informative abstracts for extended and more complex abstracts and descriptive ones for simpler and shorter research papers.
What are the Characteristics of a Good Abstract?
- A good abstract clearly defines the goals and purposes of the study.
- It should clearly describe the research methodology with a primary focus on data gathering, processing, and subsequent analysis.
- A good abstract should provide specific research findings.
- It presents the principal conclusions of the systematic study.
- It should be concise, clear, and relevant to the field of study.
- A well-designed abstract should be unifying and coherent.
- It is easy to grasp and free of technical jargon.
- It is written impartially and objectively.
What are the various sections of an ideal Abstract?
By now, you must have gained some concrete idea of the essential elements that your abstract needs to convey . Accordingly, the information is broken down into six key sections of the abstract, which include:
An Introduction or Background
Research methodology, objectives and goals, limitations.
Let's go over them in detail.
The introduction, also known as background, is the most concise part of your abstract. Ideally, it comprises a couple of sentences. Some researchers only write one sentence to introduce their abstract. The idea behind this is to guide readers through the key factors that led to your study.
It's understandable that this information might seem difficult to explain in a couple of sentences. For example, think about the following two questions like the background of your study:
- What is currently available about the subject with respect to the paper being discussed?
- What isn't understood about this issue? (This is the subject of your research)
While writing the abstract’s introduction, make sure that it is not lengthy. Because if it crosses the word limit, it may eat up the words meant to be used for providing other key information.
Research methodology is where you describe the theories and techniques you used in your research. It is recommended that you describe what you have done and the method you used to get your thorough investigation results. Certainly, it is the second-longest paragraph in the abstract.
In the research methodology section, it is essential to mention the kind of research you conducted; for instance, qualitative research or quantitative research (this will guide your research methodology too) . If you've conducted quantitative research, your abstract should contain information like the sample size, data collection method, sampling techniques, and duration of the study. Likewise, your abstract should reflect observational data, opinions, questionnaires (especially the non-numerical data) if you work on qualitative research.
The research objectives and goals speak about what you intend to accomplish with your research. The majority of research projects focus on the long-term effects of a project, and the goals focus on the immediate, short-term outcomes of the research. It is possible to summarise both in just multiple sentences.
In stating your objectives and goals, you give readers a picture of the scope of the study, its depth and the direction your research ultimately follows. Your readers can evaluate the results of your research against the goals and stated objectives to determine if you have achieved the goal of your research.
In the end, your readers are more attracted by the results you've obtained through your study. Therefore, you must take the time to explain each relevant result and explain how they impact your research. The results section exists as the longest in your abstract, and nothing should diminish its reach or quality.
One of the most important things you should adhere to is to spell out details and figures on the results of your research.
Instead of making a vague assertion such as, "We noticed that response rates varied greatly between respondents with high incomes and those with low incomes", Try these: "The response rate was higher for high-income respondents than those with lower incomes (59 30 percent vs. 30 percent in both cases; P<0.01)."
You're likely to encounter certain obstacles during your research. It could have been during data collection or even during conducting the sample . Whatever the issue, it's essential to inform your readers about them and their effects on the research.
Research limitations offer an opportunity to suggest further and deep research. If, for instance, you were forced to change for convenient sampling and snowball samples because of difficulties in reaching well-suited research participants, then you should mention this reason when you write your research abstract. In addition, a lack of prior studies on the subject could hinder your research.
Your conclusion should include the same number of sentences to wrap the abstract as the introduction. The majority of researchers offer an idea of the consequences of their research in this case.
Your conclusion should include three essential components:
- A significant take-home message.
- Corresponding important findings.
- The Interpretation.
Even though the conclusion of your abstract needs to be brief, it can have an enormous influence on the way that readers view your research. Therefore, make use of this section to reinforce the central message from your research. Be sure that your statements reflect the actual results and the methods you used to conduct your research.
Good Abstract Examples
Abstract example #1.
Children’s consumption behavior in response to food product placements in movies.
The abstract:
"Almost all research into the effects of brand placements on children has focused on the brand's attitudes or behavior intentions. Based on the significant differences between attitudes and behavioral intentions on one hand and actual behavior on the other hand, this study examines the impact of placements by brands on children's eating habits. Children aged 6-14 years old were shown an excerpt from the popular film Alvin and the Chipmunks and were shown places for the item Cheese Balls. Three different versions were developed with no placements, one with moderately frequent placements and the third with the highest frequency of placement. The results revealed that exposure to high-frequency places had a profound effect on snack consumption, however, there was no impact on consumer attitudes towards brands or products. The effects were not dependent on the age of the children. These findings are of major importance to researchers studying consumer behavior as well as nutrition experts as well as policy regulators."
Abstract Example #2
Social comparisons on social media: The impact of Facebook on young women’s body image concerns and mood. The abstract:
"The research conducted in this study investigated the effects of Facebook use on women's moods and body image if the effects are different from an internet-based fashion journal and if the appearance comparison tendencies moderate one or more of these effects. Participants who were female ( N = 112) were randomly allocated to spend 10 minutes exploring their Facebook account or a magazine's website or an appearance neutral control website prior to completing state assessments of body dissatisfaction, mood, and differences in appearance (weight-related and facial hair, face, and skin). Participants also completed a test of the tendency to compare appearances. The participants who used Facebook were reported to be more depressed than those who stayed on the control site. In addition, women who have the tendency to compare appearances reported more facial, hair and skin-related issues following Facebook exposure than when they were exposed to the control site. Due to its popularity it is imperative to conduct more research to understand the effect that Facebook affects the way people view themselves."
Abstract Example #3
The Relationship Between Cell Phone Use and Academic Performance in a Sample of U.S. College Students
"The cellphone is always present on campuses of colleges and is often utilised in situations in which learning takes place. The study examined the connection between the use of cell phones and the actual grades point average (GPA) after adjusting for predictors that are known to be a factor. In the end 536 students in the undergraduate program from 82 self-reported majors of an enormous, public institution were studied. Hierarchical analysis ( R 2 = .449) showed that use of mobile phones is significantly ( p < .001) and negative (b equal to -.164) connected to the actual college GPA, after taking into account factors such as demographics, self-efficacy in self-regulated learning, self-efficacy to improve academic performance, and the actual high school GPA that were all important predictors ( p < .05). Therefore, after adjusting for other known predictors increasing cell phone usage was associated with lower academic performance. While more research is required to determine the mechanisms behind these results, they suggest the need to educate teachers and students to the possible academic risks that are associated with high-frequency mobile phone usage."
Quick tips on writing a good abstract
There exists a common dilemma among early age researchers whether to write the abstract at first or last? However, it's recommended to compose your abstract when you've completed the research since you'll have all the information to give to your readers. You can, however, write a draft at the beginning of your research and add in any gaps later.
If you find abstract writing a herculean task, here are the few tips to help you with it:
1. Always develop a framework to support your abstract
Before writing, ensure you create a clear outline for your abstract. Divide it into sections and draw the primary and supporting elements in each one. You can include keywords and a few sentences that convey the essence of your message.
2. Review Other Abstracts
Abstracts are among the most frequently used research documents, and thousands of them were written in the past. Therefore, prior to writing yours, take a look at some examples from other abstracts. There are plenty of examples of abstracts for dissertations in the dissertation and thesis databases.
3. Avoid Jargon To the Maximum
When you write your abstract, focus on simplicity over formality. You should write in simple language, and avoid excessive filler words or ambiguous sentences. Keep in mind that your abstract must be readable to those who aren't acquainted with your subject.
4. Focus on Your Research
It's a given fact that the abstract you write should be about your research and the findings you've made. It is not the right time to mention secondary and primary data sources unless it's absolutely required.
Conclusion: How to Structure an Interesting Abstract?
Abstracts are a short outline of your essay. However, it's among the most important, if not the most important. The process of writing an abstract is not straightforward. A few early-age researchers tend to begin by writing it, thinking they are doing it to "tease" the next step (the document itself). However, it is better to treat it as a spoiler.
The simple, concise style of the abstract lends itself to a well-written and well-investigated study. If your research paper doesn't provide definitive results, or the goal of your research is questioned, so will the abstract. Thus, only write your abstract after witnessing your findings and put your findings in the context of a larger scenario.
The process of writing an abstract can be daunting, but with these guidelines, you will succeed. The most efficient method of writing an excellent abstract is to centre the primary points of your abstract, including the research question and goals methods, as well as key results.
Interested in learning more about dedicated research solutions? Go to the SciSpace product page to find out how our suite of products can help you simplify your research workflows so you can focus on advancing science.
![analyze the sample abstract of the research paper below Literature search in Scispace](https://typeset.io/resources/content/images/2022/07/34e-15.jpg)
The best-in-class solution is equipped with features such as literature search and discovery, profile management, research writing and formatting, and so much more.
But before you go,
You might also like.
![analyze the sample abstract of the research paper below Consensus GPT vs. SciSpace GPT: Choose the Best GPT for Research](https://typeset.io/resources/content/images/size/w1000/2024/02/scispace-gpt-vs-consensus-gpt.png)
Consensus GPT vs. SciSpace GPT: Choose the Best GPT for Research
Literature Review and Theoretical Framework: Understanding the Differences
![analyze the sample abstract of the research paper below Nikhil Seethi](https://typeset.io/resources/content/images/size/w100/2023/11/NIKHILS.png)
Types of Essays in Academic Writing - Quick Guide (2024)
![analyze the sample abstract of the research paper below The Writing Center • University of North Carolina at Chapel Hill](https://writingcenter.unc.edu/wp-content/uploads/sites/346/2018/08/writingcenterlogo-oneline.png)
What this handout is about
This handout provides definitions and examples of the two main types of abstracts: descriptive and informative. It also provides guidelines for constructing an abstract and general tips for you to keep in mind when drafting. Finally, it includes a few examples of abstracts broken down into their component parts.
What is an abstract?
An abstract is a self-contained, short, and powerful statement that describes a larger work. Components vary according to discipline. An abstract of a social science or scientific work may contain the scope, purpose, results, and contents of the work. An abstract of a humanities work may contain the thesis, background, and conclusion of the larger work. An abstract is not a review, nor does it evaluate the work being abstracted. While it contains key words found in the larger work, the abstract is an original document rather than an excerpted passage.
Why write an abstract?
You may write an abstract for various reasons. The two most important are selection and indexing. Abstracts allow readers who may be interested in a longer work to quickly decide whether it is worth their time to read it. Also, many online databases use abstracts to index larger works. Therefore, abstracts should contain keywords and phrases that allow for easy searching.
Say you are beginning a research project on how Brazilian newspapers helped Brazil’s ultra-liberal president Luiz Ignácio da Silva wrest power from the traditional, conservative power base. A good first place to start your research is to search Dissertation Abstracts International for all dissertations that deal with the interaction between newspapers and politics. “Newspapers and politics” returned 569 hits. A more selective search of “newspapers and Brazil” returned 22 hits. That is still a fair number of dissertations. Titles can sometimes help winnow the field, but many titles are not very descriptive. For example, one dissertation is titled “Rhetoric and Riot in Rio de Janeiro.” It is unclear from the title what this dissertation has to do with newspapers in Brazil. One option would be to download or order the entire dissertation on the chance that it might speak specifically to the topic. A better option is to read the abstract. In this case, the abstract reveals the main focus of the dissertation:
This dissertation examines the role of newspaper editors in the political turmoil and strife that characterized late First Empire Rio de Janeiro (1827-1831). Newspaper editors and their journals helped change the political culture of late First Empire Rio de Janeiro by involving the people in the discussion of state. This change in political culture is apparent in Emperor Pedro I’s gradual loss of control over the mechanisms of power. As the newspapers became more numerous and powerful, the Emperor lost his legitimacy in the eyes of the people. To explore the role of the newspapers in the political events of the late First Empire, this dissertation analyzes all available newspapers published in Rio de Janeiro from 1827 to 1831. Newspapers and their editors were leading forces in the effort to remove power from the hands of the ruling elite and place it under the control of the people. In the process, newspapers helped change how politics operated in the constitutional monarchy of Brazil.
From this abstract you now know that although the dissertation has nothing to do with modern Brazilian politics, it does cover the role of newspapers in changing traditional mechanisms of power. After reading the abstract, you can make an informed judgment about whether the dissertation would be worthwhile to read.
Besides selection, the other main purpose of the abstract is for indexing. Most article databases in the online catalog of the library enable you to search abstracts. This allows for quick retrieval by users and limits the extraneous items recalled by a “full-text” search. However, for an abstract to be useful in an online retrieval system, it must incorporate the key terms that a potential researcher would use to search. For example, if you search Dissertation Abstracts International using the keywords “France” “revolution” and “politics,” the search engine would search through all the abstracts in the database that included those three words. Without an abstract, the search engine would be forced to search titles, which, as we have seen, may not be fruitful, or else search the full text. It’s likely that a lot more than 60 dissertations have been written with those three words somewhere in the body of the entire work. By incorporating keywords into the abstract, the author emphasizes the central topics of the work and gives prospective readers enough information to make an informed judgment about the applicability of the work.
When do people write abstracts?
- when submitting articles to journals, especially online journals
- when applying for research grants
- when writing a book proposal
- when completing the Ph.D. dissertation or M.A. thesis
- when writing a proposal for a conference paper
- when writing a proposal for a book chapter
Most often, the author of the entire work (or prospective work) writes the abstract. However, there are professional abstracting services that hire writers to draft abstracts of other people’s work. In a work with multiple authors, the first author usually writes the abstract. Undergraduates are sometimes asked to draft abstracts of books/articles for classmates who have not read the larger work.
Types of abstracts
There are two types of abstracts: descriptive and informative. They have different aims, so as a consequence they have different components and styles. There is also a third type called critical, but it is rarely used. If you want to find out more about writing a critique or a review of a work, see the UNC Writing Center handout on writing a literature review . If you are unsure which type of abstract you should write, ask your instructor (if the abstract is for a class) or read other abstracts in your field or in the journal where you are submitting your article.
Descriptive abstracts
A descriptive abstract indicates the type of information found in the work. It makes no judgments about the work, nor does it provide results or conclusions of the research. It does incorporate key words found in the text and may include the purpose, methods, and scope of the research. Essentially, the descriptive abstract describes the work being abstracted. Some people consider it an outline of the work, rather than a summary. Descriptive abstracts are usually very short—100 words or less.
Informative abstracts
The majority of abstracts are informative. While they still do not critique or evaluate a work, they do more than describe it. A good informative abstract acts as a surrogate for the work itself. That is, the writer presents and explains all the main arguments and the important results and evidence in the complete article/paper/book. An informative abstract includes the information that can be found in a descriptive abstract (purpose, methods, scope) but also includes the results and conclusions of the research and the recommendations of the author. The length varies according to discipline, but an informative abstract is rarely more than 10% of the length of the entire work. In the case of a longer work, it may be much less.
Here are examples of a descriptive and an informative abstract of this handout on abstracts . Descriptive abstract:
The two most common abstract types—descriptive and informative—are described and examples of each are provided.
Informative abstract:
Abstracts present the essential elements of a longer work in a short and powerful statement. The purpose of an abstract is to provide prospective readers the opportunity to judge the relevance of the longer work to their projects. Abstracts also include the key terms found in the longer work and the purpose and methods of the research. Authors abstract various longer works, including book proposals, dissertations, and online journal articles. There are two main types of abstracts: descriptive and informative. A descriptive abstract briefly describes the longer work, while an informative abstract presents all the main arguments and important results. This handout provides examples of various types of abstracts and instructions on how to construct one.
Which type should I use?
Your best bet in this case is to ask your instructor or refer to the instructions provided by the publisher. You can also make a guess based on the length allowed; i.e., 100-120 words = descriptive; 250+ words = informative.
How do I write an abstract?
The format of your abstract will depend on the work being abstracted. An abstract of a scientific research paper will contain elements not found in an abstract of a literature article, and vice versa. However, all abstracts share several mandatory components, and there are also some optional parts that you can decide to include or not. When preparing to draft your abstract, keep the following key process elements in mind:
- Reason for writing: What is the importance of the research? Why would a reader be interested in the larger work?
- Problem: What problem does this work attempt to solve? What is the scope of the project? What is the main argument/thesis/claim?
- Methodology: An abstract of a scientific work may include specific models or approaches used in the larger study. Other abstracts may describe the types of evidence used in the research.
- Results: Again, an abstract of a scientific work may include specific data that indicates the results of the project. Other abstracts may discuss the findings in a more general way.
- Implications: What changes should be implemented as a result of the findings of the work? How does this work add to the body of knowledge on the topic?
(This list of elements is adapted with permission from Philip Koopman, “How to Write an Abstract.” )
All abstracts include:
- A full citation of the source, preceding the abstract.
- The most important information first.
- The same type and style of language found in the original, including technical language.
- Key words and phrases that quickly identify the content and focus of the work.
- Clear, concise, and powerful language.
Abstracts may include:
- The thesis of the work, usually in the first sentence.
- Background information that places the work in the larger body of literature.
- The same chronological structure as the original work.
How not to write an abstract:
- Do not refer extensively to other works.
- Do not add information not contained in the original work.
- Do not define terms.
If you are abstracting your own writing
When abstracting your own work, it may be difficult to condense a piece of writing that you have agonized over for weeks (or months, or even years) into a 250-word statement. There are some tricks that you could use to make it easier, however.
Reverse outlining:
This technique is commonly used when you are having trouble organizing your own writing. The process involves writing down the main idea of each paragraph on a separate piece of paper– see our short video . For the purposes of writing an abstract, try grouping the main ideas of each section of the paper into a single sentence. Practice grouping ideas using webbing or color coding .
For a scientific paper, you may have sections titled Purpose, Methods, Results, and Discussion. Each one of these sections will be longer than one paragraph, but each is grouped around a central idea. Use reverse outlining to discover the central idea in each section and then distill these ideas into one statement.
Cut and paste:
To create a first draft of an abstract of your own work, you can read through the entire paper and cut and paste sentences that capture key passages. This technique is useful for social science research with findings that cannot be encapsulated by neat numbers or concrete results. A well-written humanities draft will have a clear and direct thesis statement and informative topic sentences for paragraphs or sections. Isolate these sentences in a separate document and work on revising them into a unified paragraph.
If you are abstracting someone else’s writing
When abstracting something you have not written, you cannot summarize key ideas just by cutting and pasting. Instead, you must determine what a prospective reader would want to know about the work. There are a few techniques that will help you in this process:
Identify key terms:
Search through the entire document for key terms that identify the purpose, scope, and methods of the work. Pay close attention to the Introduction (or Purpose) and the Conclusion (or Discussion). These sections should contain all the main ideas and key terms in the paper. When writing the abstract, be sure to incorporate the key terms.
Highlight key phrases and sentences:
Instead of cutting and pasting the actual words, try highlighting sentences or phrases that appear to be central to the work. Then, in a separate document, rewrite the sentences and phrases in your own words.
Don’t look back:
After reading the entire work, put it aside and write a paragraph about the work without referring to it. In the first draft, you may not remember all the key terms or the results, but you will remember what the main point of the work was. Remember not to include any information you did not get from the work being abstracted.
Revise, revise, revise
No matter what type of abstract you are writing, or whether you are abstracting your own work or someone else’s, the most important step in writing an abstract is to revise early and often. When revising, delete all extraneous words and incorporate meaningful and powerful words. The idea is to be as clear and complete as possible in the shortest possible amount of space. The Word Count feature of Microsoft Word can help you keep track of how long your abstract is and help you hit your target length.
Example 1: Humanities abstract
Kenneth Tait Andrews, “‘Freedom is a constant struggle’: The dynamics and consequences of the Mississippi Civil Rights Movement, 1960-1984” Ph.D. State University of New York at Stony Brook, 1997 DAI-A 59/02, p. 620, Aug 1998
This dissertation examines the impacts of social movements through a multi-layered study of the Mississippi Civil Rights Movement from its peak in the early 1960s through the early 1980s. By examining this historically important case, I clarify the process by which movements transform social structures and the constraints movements face when they try to do so. The time period studied includes the expansion of voting rights and gains in black political power, the desegregation of public schools and the emergence of white-flight academies, and the rise and fall of federal anti-poverty programs. I use two major research strategies: (1) a quantitative analysis of county-level data and (2) three case studies. Data have been collected from archives, interviews, newspapers, and published reports. This dissertation challenges the argument that movements are inconsequential. Some view federal agencies, courts, political parties, or economic elites as the agents driving institutional change, but typically these groups acted in response to the leverage brought to bear by the civil rights movement. The Mississippi movement attempted to forge independent structures for sustaining challenges to local inequities and injustices. By propelling change in an array of local institutions, movement infrastructures had an enduring legacy in Mississippi.
Now let’s break down this abstract into its component parts to see how the author has distilled his entire dissertation into a ~200 word abstract.
What the dissertation does This dissertation examines the impacts of social movements through a multi-layered study of the Mississippi Civil Rights Movement from its peak in the early 1960s through the early 1980s. By examining this historically important case, I clarify the process by which movements transform social structures and the constraints movements face when they try to do so.
How the dissertation does it The time period studied in this dissertation includes the expansion of voting rights and gains in black political power, the desegregation of public schools and the emergence of white-flight academies, and the rise and fall of federal anti-poverty programs. I use two major research strategies: (1) a quantitative analysis of county-level data and (2) three case studies.
What materials are used Data have been collected from archives, interviews, newspapers, and published reports.
Conclusion This dissertation challenges the argument that movements are inconsequential. Some view federal agencies, courts, political parties, or economic elites as the agents driving institutional change, but typically these groups acted in response to movement demands and the leverage brought to bear by the civil rights movement. The Mississippi movement attempted to forge independent structures for sustaining challenges to local inequities and injustices. By propelling change in an array of local institutions, movement infrastructures had an enduring legacy in Mississippi.
Keywords social movements Civil Rights Movement Mississippi voting rights desegregation
Example 2: Science Abstract
Luis Lehner, “Gravitational radiation from black hole spacetimes” Ph.D. University of Pittsburgh, 1998 DAI-B 59/06, p. 2797, Dec 1998
The problem of detecting gravitational radiation is receiving considerable attention with the construction of new detectors in the United States, Europe, and Japan. The theoretical modeling of the wave forms that would be produced in particular systems will expedite the search for and analysis of detected signals. The characteristic formulation of GR is implemented to obtain an algorithm capable of evolving black holes in 3D asymptotically flat spacetimes. Using compactification techniques, future null infinity is included in the evolved region, which enables the unambiguous calculation of the radiation produced by some compact source. A module to calculate the waveforms is constructed and included in the evolution algorithm. This code is shown to be second-order convergent and to handle highly non-linear spacetimes. In particular, we have shown that the code can handle spacetimes whose radiation is equivalent to a galaxy converting its whole mass into gravitational radiation in one second. We further use the characteristic formulation to treat the region close to the singularity in black hole spacetimes. The code carefully excises a region surrounding the singularity and accurately evolves generic black hole spacetimes with apparently unlimited stability.
This science abstract covers much of the same ground as the humanities one, but it asks slightly different questions.
Why do this study The problem of detecting gravitational radiation is receiving considerable attention with the construction of new detectors in the United States, Europe, and Japan. The theoretical modeling of the wave forms that would be produced in particular systems will expedite the search and analysis of the detected signals.
What the study does The characteristic formulation of GR is implemented to obtain an algorithm capable of evolving black holes in 3D asymptotically flat spacetimes. Using compactification techniques, future null infinity is included in the evolved region, which enables the unambiguous calculation of the radiation produced by some compact source. A module to calculate the waveforms is constructed and included in the evolution algorithm.
Results This code is shown to be second-order convergent and to handle highly non-linear spacetimes. In particular, we have shown that the code can handle spacetimes whose radiation is equivalent to a galaxy converting its whole mass into gravitational radiation in one second. We further use the characteristic formulation to treat the region close to the singularity in black hole spacetimes. The code carefully excises a region surrounding the singularity and accurately evolves generic black hole spacetimes with apparently unlimited stability.
Keywords gravitational radiation (GR) spacetimes black holes
Works consulted
We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.
Belcher, Wendy Laura. 2009. Writing Your Journal Article in Twelve Weeks: A Guide to Academic Publishing Success. Thousand Oaks, CA: Sage Press.
Koopman, Philip. 1997. “How to Write an Abstract.” Carnegie Mellon University. October 1997. http://users.ece.cmu.edu/~koopman/essays/abstract.html .
Lancaster, F.W. 2003. Indexing And Abstracting in Theory and Practice , 3rd ed. London: Facet Publishing.
You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill
Make a Gift
- USC Libraries
- Research Guides
Organizing Your Social Sciences Research Paper
- 3. The Abstract
- Purpose of Guide
- Design Flaws to Avoid
- Independent and Dependent Variables
- Glossary of Research Terms
- Reading Research Effectively
- Narrowing a Topic Idea
- Broadening a Topic Idea
- Extending the Timeliness of a Topic Idea
- Academic Writing Style
- Applying Critical Thinking
- Choosing a Title
- Making an Outline
- Paragraph Development
- Research Process Video Series
- Executive Summary
- The C.A.R.S. Model
- Background Information
- The Research Problem/Question
- Theoretical Framework
- Citation Tracking
- Content Alert Services
- Evaluating Sources
- Primary Sources
- Secondary Sources
- Tiertiary Sources
- Scholarly vs. Popular Publications
- Qualitative Methods
- Quantitative Methods
- Insiderness
- Using Non-Textual Elements
- Limitations of the Study
- Common Grammar Mistakes
- Writing Concisely
- Avoiding Plagiarism
- Footnotes or Endnotes?
- Further Readings
- Generative AI and Writing
- USC Libraries Tutorials and Other Guides
- Bibliography
An abstract summarizes, usually in one paragraph of 300 words or less, the major aspects of the entire paper in a prescribed sequence that includes: 1) the overall purpose of the study and the research problem(s) you investigated; 2) the basic design of the study; 3) major findings or trends found as a result of your analysis; and, 4) a brief summary of your interpretations and conclusions.
Writing an Abstract. The Writing Center. Clarion University, 2009; Writing an Abstract for Your Research Paper. The Writing Center, University of Wisconsin, Madison; Koltay, Tibor. Abstracts and Abstracting: A Genre and Set of Skills for the Twenty-first Century . Oxford, UK: Chandos Publishing, 2010;
Importance of a Good Abstract
Sometimes your professor will ask you to include an abstract, or general summary of your work, with your research paper. The abstract allows you to elaborate upon each major aspect of the paper and helps readers decide whether they want to read the rest of the paper. Therefore, enough key information [e.g., summary results, observations, trends, etc.] must be included to make the abstract useful to someone who may want to examine your work.
How do you know when you have enough information in your abstract? A simple rule-of-thumb is to imagine that you are another researcher doing a similar study. Then ask yourself: if your abstract was the only part of the paper you could access, would you be happy with the amount of information presented there? Does it tell the whole story about your study? If the answer is "no" then the abstract likely needs to be revised.
Farkas, David K. “A Scheme for Understanding and Writing Summaries.” Technical Communication 67 (August 2020): 45-60; How to Write a Research Abstract. Office of Undergraduate Research. University of Kentucky; Staiger, David L. “What Today’s Students Need to Know about Writing Abstracts.” International Journal of Business Communication January 3 (1966): 29-33; Swales, John M. and Christine B. Feak. Abstracts and the Writing of Abstracts . Ann Arbor, MI: University of Michigan Press, 2009.
Structure and Writing Style
I. Types of Abstracts
To begin, you need to determine which type of abstract you should include with your paper. There are four general types.
Critical Abstract A critical abstract provides, in addition to describing main findings and information, a judgment or comment about the study’s validity, reliability, or completeness. The researcher evaluates the paper and often compares it with other works on the same subject. Critical abstracts are generally 400-500 words in length due to the additional interpretive commentary. These types of abstracts are used infrequently.
Descriptive Abstract A descriptive abstract indicates the type of information found in the work. It makes no judgments about the work, nor does it provide results or conclusions of the research. It does incorporate key words found in the text and may include the purpose, methods, and scope of the research. Essentially, the descriptive abstract only describes the work being summarized. Some researchers consider it an outline of the work, rather than a summary. Descriptive abstracts are usually very short, 100 words or less. Informative Abstract The majority of abstracts are informative. While they still do not critique or evaluate a work, they do more than describe it. A good informative abstract acts as a surrogate for the work itself. That is, the researcher presents and explains all the main arguments and the important results and evidence in the paper. An informative abstract includes the information that can be found in a descriptive abstract [purpose, methods, scope] but it also includes the results and conclusions of the research and the recommendations of the author. The length varies according to discipline, but an informative abstract is usually no more than 300 words in length.
Highlight Abstract A highlight abstract is specifically written to attract the reader’s attention to the study. No pretense is made of there being either a balanced or complete picture of the paper and, in fact, incomplete and leading remarks may be used to spark the reader’s interest. In that a highlight abstract cannot stand independent of its associated article, it is not a true abstract and, therefore, rarely used in academic writing.
II. Writing Style
Use the active voice when possible , but note that much of your abstract may require passive sentence constructions. Regardless, write your abstract using concise, but complete, sentences. Get to the point quickly and always use the past tense because you are reporting on a study that has been completed.
Abstracts should be formatted as a single paragraph in a block format and with no paragraph indentations. In most cases, the abstract page immediately follows the title page. Do not number the page. Rules set forth in writing manual vary but, in general, you should center the word "Abstract" at the top of the page with double spacing between the heading and the abstract. The final sentences of an abstract concisely summarize your study’s conclusions, implications, or applications to practice and, if appropriate, can be followed by a statement about the need for additional research revealed from the findings.
Composing Your Abstract
Although it is the first section of your paper, the abstract should be written last since it will summarize the contents of your entire paper. A good strategy to begin composing your abstract is to take whole sentences or key phrases from each section of the paper and put them in a sequence that summarizes the contents. Then revise or add connecting phrases or words to make the narrative flow clearly and smoothly. Note that statistical findings should be reported parenthetically [i.e., written in parentheses].
Before handing in your final paper, check to make sure that the information in the abstract completely agrees with what you have written in the paper. Think of the abstract as a sequential set of complete sentences describing the most crucial information using the fewest necessary words. The abstract SHOULD NOT contain:
- A catchy introductory phrase, provocative quote, or other device to grab the reader's attention,
- Lengthy background or contextual information,
- Redundant phrases, unnecessary adverbs and adjectives, and repetitive information;
- Acronyms or abbreviations,
- References to other literature [say something like, "current research shows that..." or "studies have indicated..."],
- Using ellipticals [i.e., ending with "..."] or incomplete sentences,
- Jargon or terms that may be confusing to the reader,
- Citations to other works, and
- Any sort of image, illustration, figure, or table, or references to them.
Abstract. Writing Center. University of Kansas; Abstract. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Abstracts. The Writing Center. University of North Carolina; Borko, Harold and Seymour Chatman. "Criteria for Acceptable Abstracts: A Survey of Abstracters' Instructions." American Documentation 14 (April 1963): 149-160; Abstracts. The Writer’s Handbook. Writing Center. University of Wisconsin, Madison; Hartley, James and Lucy Betts. "Common Weaknesses in Traditional Abstracts in the Social Sciences." Journal of the American Society for Information Science and Technology 60 (October 2009): 2010-2018; Koltay, Tibor. Abstracts and Abstracting: A Genre and Set of Skills for the Twenty-first Century. Oxford, UK: Chandos Publishing, 2010; Procter, Margaret. The Abstract. University College Writing Centre. University of Toronto; Riordan, Laura. “Mastering the Art of Abstracts.” The Journal of the American Osteopathic Association 115 (January 2015 ): 41-47; Writing Report Abstracts. The Writing Lab and The OWL. Purdue University; Writing Abstracts. Writing Tutorial Services, Center for Innovative Teaching and Learning. Indiana University; Koltay, Tibor. Abstracts and Abstracting: A Genre and Set of Skills for the Twenty-First Century . Oxford, UK: 2010; Writing an Abstract for Your Research Paper. The Writing Center, University of Wisconsin, Madison.
Writing Tip
Never Cite Just the Abstract!
Citing to just a journal article's abstract does not confirm for the reader that you have conducted a thorough or reliable review of the literature. If the full-text is not available, go to the USC Libraries main page and enter the title of the article [NOT the title of the journal]. If the Libraries have a subscription to the journal, the article should appear with a link to the full-text or to the journal publisher page where you can get the article. If the article does not appear, try searching Google Scholar using the link on the USC Libraries main page. If you still can't find the article after doing this, contact a librarian or you can request it from our free i nterlibrary loan and document delivery service .
- << Previous: Research Process Video Series
- Next: Executive Summary >>
- Last Updated: Jul 3, 2024 10:07 AM
- URL: https://libguides.usc.edu/writingguide
- Link to facebook
- Link to linkedin
- Link to twitter
- Link to youtube
- Writing Tips
How to Write an Abstract in APA Format
![analyze the sample abstract of the research paper below How to Write an Abstract in APA Format](https://proofed.com/wp-content/webp-express/webp-images/uploads/2023/10/2-Graphic-How-to-Write-an-Abstract-in-APA-Format-628x492.png.webp)
3-minute read
- 2nd November 2023
If you’re writing an in-depth research paper following APA guidelines, you most likely need to include an abstract . If you’re confused about where to start – don’t be. We’ve got you covered! In this post, we’ll walk you through the steps of formatting and writing an abstract in APA format.
What Is an Abstract?
An abstract is a brief summary of a larger academic text, such as a thesis, dissertation, or research paper, typically located at the very beginning of the paper before the introduction. Its main purpose is to give readers a clear and concise overview of your key points, objectives, results, and conclusion. Essentially, it lets the reader know the purpose and premise of your study and what to expect from your paper.
How to Write an Abstract Using APA Style
If you’re following APA guidelines, your abstract should include:
● Your clearly stated hypothesis or hypotheses
● The key takeaways of the literature review
● Your research questions and/or objectives
● The methods used in your study
● The research design and sample/sample size
● Your results and key findings
● The significance of your study and the implications of your findings
Note that you should provide a short overview of these points and not an in-depth analysis (which will come later in your paper) – each should be around one to two sentences long. The total length will vary depending on a variety of factors, such as your university/journal specifications, topic, and the length of your paper, but APA guidelines recommend that abstracts shouldn’t exceed 250 words.
Find this useful?
Subscribe to our newsletter and get writing tips from our editors straight to your inbox.
How to Format an Abstract in APA Format
How should you format your abstract if you’re using APA style? To start, the abstract should be located on the second page of your paper, after the title page. To format your abstract:
● Set one-inch margins on all sides.
● Label the section “Abstract” on the first line of the page, centered, and using bold font.
● Use a clear, readable, widely available font, such as Times New Roman (12 pt.) or Calibri (11 pt.).
● Begin writing the text one line below the “Abstract” label.
● Do not indent and write text as a single paragraph.
APA guidelines state that three to five keywords can be included at the end of your abstract, which makes your paper searchable in a database. Be sure to choose brief, relevant keywords or phrases that reflect the most important aspects of your study. Keywords should be written one line below the text of the abstract immediately following the label “Keywords” in italics . Keywords can be listed in any order and should be separated using commas.
For example, for a journal article titled Biodiversity and Environmental Resilience: Strategies for Sustainability , the keywords section could look like this:
Note that keywords should be written in lowercase (unless they’re proper nouns) and no end punctuation is necessary after the final keyword.
If you want to ensure your abstract grabs your reader’s attention and leaves a lasting impression, then have it professionally proofread by our expert team. Our editors are skilled at editing a wide range of academic subjects – from astronomy to zoology. Send in your free sample to get started today!
Share this article:
Post A New Comment
Got content that needs a quick turnaround? Let us polish your work. Explore our editorial business services.
9-minute read
How to Use Infographics to Boost Your Presentation
Is your content getting noticed? Capturing and maintaining an audience’s attention is a challenge when...
8-minute read
Why Interactive PDFs Are Better for Engagement
Are you looking to enhance engagement and captivate your audience through your professional documents? Interactive...
7-minute read
Seven Key Strategies for Voice Search Optimization
Voice search optimization is rapidly shaping the digital landscape, requiring content professionals to adapt their...
4-minute read
Five Creative Ways to Showcase Your Digital Portfolio
Are you a creative freelancer looking to make a lasting impression on potential clients or...
How to Ace Slack Messaging for Contractors and Freelancers
Effective professional communication is an important skill for contractors and freelancers navigating remote work environments....
How to Insert a Text Box in a Google Doc
Google Docs is a powerful collaborative tool, and mastering its features can significantly enhance your...
![analyze the sample abstract of the research paper below Logo Harvard University](https://proofed.com/wp-content/webp-express/webp-images/uploads/2020/11/logo-harvard.png.webp)
Make sure your writing is the best it can be with our expert English proofreading and editing.
![analyze the sample abstract of the research paper below Main Chegg Logo](https://cheggwriting.wpengine.com/wp-content/themes/chegg-writing/dist/images/logo.png'))
Writing an abstract in APA format
Published October 23, 2020. Updated August 30, 2021.
What is an abstract?
An abstract is a short but comprehensive summary of a research paper that presents a brief overview of the paper’s main points . Most scholarly journals require that an abstract be included in any of their paper submissions , but abstracts are not typically required for student papers. Only include an abstract in your paper if your professor or instructor specifically included it in their assignment instructions.
While abstracts are supposed to be short and direct, they also must be factual and well written, and should detai l the major points that the paper is trying to make. An impactful and well-written abstract can win you a good first impression with your reader.
As a researcher yourself, an abstract can help you decide whether a paper or article you are reading is applicable to your research topic. They are a great way to determine whether the rest of the source is something you may want to reference in your paper.
Because an abstract is such an essential part of any paper, it is important to follow the proper formatting guidelines . Writing your abstract according to the prescribed format will help you get the best grade on your paper .
For help writing your essay, research paper , or other project, check out these writing tips .
How to write an abstract in APA format
In APA format, t he abstract is p lace d on a separate page , which typically comes after the title or cover page of the paper . Include the title “Abstract” at the top, bold it, and center align it.
You want to ensure your abstract is factual but concise. Therefore, limit it to 250 words or less. Be sure to include information on only the most important parts of your paper and avoid rewriting parts of your paper in their entirety. You should also avoid restating exact sentences from the body of your paper. Instead, summarize your main points.
The abstract should be written as a single paragraph and should cover the hypothesis or thesis, research methods used, results or conclusions, and implications of your topic.
Use the same font, font size , and 1-inch margins as the rest of your paper . The abstract should also be double-spaced. The text should be double spaced and not indented.
You may also want to include keywords at the bottom of your abstract. These are the most important terms you discuss in your paper.
Quick overview:
- Include the title “Abstract” at the top, bold it, and center align it.
- Limit the abstract to 250 words or less.
- Use the same font, font size, and 1-inch margins as the rest of your paper .
- Double-space your abstract, but don’t indent it.
- You have the option of including keywords at the bottom of the abstract.
Types of a bstracts and how to write them
The type of paper you are writing will determine what type of abstract you include. Here are some basic types of a bstracts and how you should write them:
Empirical papers present research based on actual experiments or observations. The a bstract for an empirical paper should present the problem being investigated, the participants or relevant subjects in the research (e.g. middle school and high school students) , and the basic findings of the research. Additionally, the abstract should talk about the essential methods of the research, such as its design (e.g. experimental or observational study) and data-gathering methods .
Replication papers should mention the study being replicated in the abstract and type of replication in the paper (e.g. direct, conceptual). The abstract should mention the scope of this replication and the conclusion it reaches.
A literature review should include an abstract that describes what type of literature is being reviewed and a general conclusion.
Theoretical papers have abstracts that describe the theory/model being followed and how it relates to the empirical results.
Qualitative or Quantitative Meta-analysis papers gather pertinent data from several studies and combine them with additional data to reach a single conclusion. These abstract s need to present the research question, the eligibility criteria for the type of studies included , and the methods for combining or comparing the data. Along with the conclusion, briefly mention the main result and its implications.
Methodological papers study data to provide different approaches for research. An abstract for this type of paper should mention a general range of the methodologies being discusse d and the essential features of the approach.
Tips for writing an abstract in APA format:
- An abstract should be accurate and should only focus on the content of the paper .
- Abstracts do not require citations.
- While writing about the conclusion of your paper or your study result s , it is preferable to use the present tense .
- Your sentences should be concise and precise. This is because an abstract is supposed to be extremely informative, while also adhering to the word limit. Keep your sentences short and sweet.
- If you are presenting any statistical or quantitative information, use the correct format for representing it. All mathematical symbols and signs should be presented in typed form.
Sample a bstract
Since abstracts are usually included with professional papers, this example includes a running head. Running heads are required for professional papers.
Key takeaways
- An abstract is a comprehensive summary that presents an overview of your paper.
- It is presented on a page of its own, and comes after the title page.
- This page includes a cent er- aligned bold heading ‘Abstract’ and a short summary (preferably less than 250 words) .
- An abstract should be concise and precise; it should address the most important details about the paper, for example, the t opic, the purpose of the study, the conclusion, etc.
- The abstract page has the same font and font size as the paper and double spacing, but is not indented.
- Keywords are an optional section of the abstract page and include the major phrases and words of the paper ( usually 3-5 words) .
- The keywords are presented below the abstract, indented, with an italici z ed label ‘ Keywords :’
APA Style Guides
APA Format: Annotated bibliography | Abstract | Block and direct quotes | Headings | Outline | Page Numbers | Sample paper | Title page
Citing Sources: In-text citations | Bibliography | Footnotes | Citing Multiple Authors | Citing Sources with No Authors | Using et al
APA Citation Generator: Article | Book | Image | Interview | Journal | Movie | PDF | Textbook | Website | YouTube
Published August 27, 2021.
![analyze the sample abstract of the research paper below Framed paper](https://cheggwriting.wpengine.com/wp-content/themes/chegg-writing/dist/images/paper-framed.jpg)
What’s included with a Chegg Writing subscription
- Unlimited number of paper scans
- Plagiarism detection: Check against billions of sources
- Expert proofreading for papers on any subject
- Grammar scans for 200+ types of common errors
- Automatically create & save citations in 7,000+ styles
- Cancel subscription anytime, no obligation
![analyze the sample abstract of the research paper below M big.jpg](https://static.wixstatic.com/media/ca561b_884dade4d122459795150709deff1c73~mv2.jpg/v1/fill/w_60,h_60,al_c,q_80,usm_0.66_1.00_0.01,enc_auto/M%20big.jpg)
Magnum Proofreading Services
- Jake Magnum
- Jan 2, 2021
![](http://cintadecorrer.fun/777/templates/cheerup1/res/banner1.gif)
Writing an Abstract for a Research Paper: Guidelines, Examples, and Templates
There are six steps to writing a standard abstract. (1) Begin with a broad statement about your topic. Then, (2) state the problem or knowledge gap related to this topic that your study explores. After that, (3) describe what specific aspect of this problem you investigated, and (4) briefly explain how you went about doing this. After that, (5) describe the most meaningful outcome(s) of your study. Finally, (6) close your abstract by explaining the broad implication(s) of your findings.
In this article, I present step-by-step guidelines for writing an abstract for an academic paper. These guidelines are fo llowed by an example of a full abstract that follows these guidelines and a few fill-in-the-blank templates that you can use to write your own abstract.
Guidelines for Writing an Abstract
The basic structure of an abstract is illustrated below.
![analyze the sample abstract of the research paper below](https://static.wixstatic.com/media/ca561b_d5fed8f9a0454685b2a96f1e31075f8a~mv2.jpg/v1/fill/w_118,h_66,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/ca561b_d5fed8f9a0454685b2a96f1e31075f8a~mv2.jpg)
A standard abstract starts with a very general statement and becomes more specific with each sentence that follows until once again making a broad statement about the study’s implications at the end. Altogether, a standard abstract has six functions, which are described in detail below.
Start by making a broad statement about your topic.
The first sentence of your abstract should briefly describe a problem that is of interest to your readers. When writing this first sentence, you should think about who comprises your target audience and use terms that will appeal to this audience. If your opening sentence is too broad, it might lose the attention of potential readers because they will not know if your study is relevant to them.
Too broad : Maintaining an ideal workplace environment has a positive effect on employees.
The sentence above is so broad that it will not grab the reader’s attention. While it gives the reader some idea of the area of study, it doesn’t provide any details about the author’s topic within their research area. This can be fixed by inserting some keywords related to the topic (these are underlined in the revised example below).
Improved : Keeping the workplace environment at an ideal temperature positively affects the overall health of employees.
The revised sentence is much better, as it expresses two points about the research topic—namely, (i) what aspect of workplace environment was studied, (ii) what aspect of employees was observed. The mention of these aspects of the research will draw the attention of readers who are interested in them.
Describe the general problem that your paper addresses.
After describing your topic in the first sentence, you can then explain what aspect of this topic has motivated your research. Often, authors use this part of the abstract to describe the research gap that they identified and aimed to fill. These types of sentences are often characterized by the use of words such as “however,” “although,” “despite,” and so on.
However, a comprehensive understanding of how different workplace bullying experiences are associated with absenteeism is currently lacking.
The above example is typical of a sentence describing the problem that a study intends to tackle. The author has noticed that there is a gap in the research, and they briefly explain this gap here.
Although it has been established that quantity and quality of sleep can affect different types of task performance and personal health, the interactions between sleep habits and workplace behaviors have received very little attention.
The example above illustrates a case in which the author has accomplished two tasks with one sentence. The first part of the sentence (up until the comma) mentions the general topic that the research fits into, while the second part (after the comma) describes the general problem that the research addresses.
Express the specific problem investigated in your paper.
After describing the general problem that motivated your research, the next sentence should express the specific aspect of the problem that you investigated. Sentences of this type are often indicated by the use of phrases like “the purpose of this research is to,” “this paper is intended to,” or “this work aims to.”
Uninformative : However, a comprehensive understanding of how different workplace bullying experiences are associated with absenteeism is currently lacking. The present article aimed to provide new insights into the relationship between workplace bullying and absenteeism .
The second sentence in the above example is a mere rewording of the first sentence. As such, it adds nothing to the abstract. The second sentence should be more specific than the preceding one.
Improved : However, a comprehensive understanding of how different workplace bullying experiences are associated with absenteeism is currently lacking. The present article aimed to define various subtypes of workplace bullying and determine which subtypes tend to lead to absenteeism .
The second sentence of this passage is much more informative than in the previous example. This sentence lets the reader know exactly what they can expect from the full research article.
Explain how you attempted to resolve your study’s specific problem.
In this part of your abstract, you should attempt to describe your study’s methodology in one or two sentences. As such, you must be sure to include only the most important information about your method. At the same time, you must also be careful not to be too vague.
Too vague : We conducted multiple tests to examine changes in various factors related to well-being.
This description of the methodology is too vague. Instead of merely mentioning “tests” and “factors,” the author should note which specific tests were run and which factors were assessed.
Improved : Using data from BHIP completers, we conducted multiple one-way multivariate analyses of variance and follow-up univariate t-tests to examine changes in physical and mental health, stress, energy levels, social satisfaction, self-efficacy, and quality of life.
This sentence is very well-written. It packs a lot of specific information about the method into a single sentence. Also, it does not describe more details than are needed for an abstract.
Briefly tell the reader what you found by carrying out your study.
This is the most important part of the abstract—the other sentences in the abstract are there to explain why this one is relevant. When writing this sentence, imagine that someone has asked you, “What did you find in your research?” and that you need to answer them in one or two sentences.
Too vague : Consistently poor sleepers had more health risks and medical conditions than consistently optimal sleepers.
This sentence is okay, but it would be helpful to let the reader know which health risks and medical conditions were related to poor sleeping habits.
Improved : Consistently poor sleepers were more likely than consistently optimal sleepers to suffer from chronic abdominal pain, and they were at a higher risk for diabetes and heart disease.
This sentence is better, as the specific health conditions are named.
Finally, describe the major implication(s) of your study.
Most abstracts end with a short sentence that explains the main takeaway(s) that you want your audience to gain from reading your paper. Often, this sentence is addressed to people in power (e.g., employers, policymakers), and it recommends a course of action that such people should take based on the results.
Too broad : Employers may wish to make use of strategies that increase employee health.
This sentence is too broad to be useful. It does not give employers a starting point to implement a change.
Improved : Employers may wish to incorporate sleep education initiatives as part of their overall health and wellness strategies.
This sentence is better than the original, as it provides employers with a starting point—specifically, it invites employers to look up information on sleep education programs.
Abstract Example
The abstract produced here is from a paper published in Electronic Commerce Research and Applications . I have made slight alterations to the abstract so that this example fits the guidelines given in this article.
(1) Gamification can strengthen enjoyment and productivity in the workplace. (2) Despite this, research on gamification in the work context is still limited. (3) In this study, we investigated the effect of gamification on the workplace enjoyment and productivity of employees by comparing employees with leadership responsibilities to those without leadership responsibilities. (4) Work-related tasks were gamified using the habit-tracking game Habitica, and data from 114 employees were gathered using an online survey. (5) The results illustrated that employees without leadership responsibilities used work gamification as a trigger for self-motivation, whereas employees with leadership responsibilities used it to improve their health. (6) Work gamification positively affected work enjoyment for both types of employees and positively affected productivity for employees with leadership responsibilities. (7) Our results underline the importance of taking work-related variables into account when researching work gamification.
In Sentence (1), the author makes a broad statement about their topic. Notice how the nouns used (“gamification,” “enjoyment,” “productivity”) are quite general while still indicating the focus of the paper. The author uses Sentence (2) to very briefly state the problem that the research will address.
In Sentence (3), the author explains what specific aspects of the problem mentioned in Sentence (2) will be explored in the present work. Notice that the mention of leadership responsibilities makes Sentence (3) more specific than Sentence (2). Sentence (4) gets even more specific, naming the specific tools used to gather data and the number of participants.
Sentences (5) and (6) are similar, with each sentence describing one of the study’s main findings. Then, suddenly, the scope of the abstract becomes quite broad again in Sentence (7), which mentions “work-related variables” instead of a specific variable and “researching” instead of a specific kind of research.
Abstract Templates
Copy and paste any of the paragraphs below into a word processor. Then insert the appropriate information to produce an abstract for your research paper.
Template #1
Researchers have established that [Make a broad statement about your area of research.] . However, [Describe the knowledge gap that your paper addresses.] . The goal of this paper is to [Describe the purpose of your paper.] . The achieve this goal, we [Briefly explain your methodology.] . We found that [Indicate the main finding(s) of your study; you may need two sentences to do this.] . [Provide a broad implication of your results.] .
Template #2
It is well-understood that [Make a broad statement about your area of research.] . Despite this, [Describe the knowledge gap that your paper addresses.] . The current research aims to [Describe the purpose of your paper.] . To accomplish this, we [Briefly explain your methodology.] . It was discovered that [Indicate the main finding(s) of your study; you may need two sentences to do this.] . [Provide a broad implication of your results.] .
Template #3
Extensive research indicates that [Make a broad statement about your area of research.] . Nevertheless, [Describe the knowledge gap that your paper addresses.] . The present work is intended to [Describe the purpose of your paper.] . To this end, we [Briefly explain your methodology.] . The results revealed that [Indicate the main finding(s) of your study; you may need two sentences to do this.] . [Provide a broad implication of your results.] .
- How to Write an Abstract
Related Posts
How to Write a Research Paper in English: A Guide for Non-native Speakers
How to Write an Abstract Quickly
Using the Present Tense and Past Tense When Writing an Abstract
![analyze the sample abstract of the research paper below Banner](https://d2jv02qf7xgjwx.cloudfront.net/sites/1583/banner/LibGuides_Banner_9.2021.png)
How to Write an Abstract : How to Format a Research Abstract MLA Style with Examples
- How to Format a Research Abstract MLA Style with Examples
- Annotations
MLA Format Research Abstract with Examples
An abstract is a concise summary of a finished research paper that motivates readers to keep reading . It is a reduced form of a lengthy piece of writing that highlights the key points and briefly describes the content and scope of the paper. An abstract in MLA format generally aims to summarize the objective, methods, discussions, and conclusions of a paper.
Abstracts are usually between 100-250 words or around 5-7 sentences depending on the type. They can include short descriptions of your motivations, objective, methods, findings, discussion, and conclusion of the paper. You can also include why you wrote the paper and why readers should be interested.
Why do you need an abstract?
Abstracts allow for a quick summary of your paper for other researchers. Busy researchers don’t have time to read everything, so they rely on the abstract to help them decide whether or not they will read the paper.
Although MLA style doesn’t require an abstract, the MLA style abstract is the most commonly used style in the humanities. If you are writing a paper for a class in literature, religion, philosophy, or other similar subjects, you should use MLA style. Check with your professor to see if an abstract is required for your paper.
Different types of abstracts
There are two different types of abstracts: descriptive and informative.
- Descriptive abstracts are approximately 100 words and give a brief overview of the paper. They do not include a full analysis and may not include the results and/or conclusions.
- Informative abstracts are longer and are approximately 150-250 words. They are a condensed version of your writing that contains information from every part of the paper.
How to write an abstract in MLA style
To write a high-quality abstract in MLA style, you will need an explanation of what research was done and what the outcomes were. Write in a clear, simple, and direct style. The abstract gives readers the information they need to decide whether to read the complete paper or not.
Here are some guidelines for writing a great abstract in MLA style:
- Finish the paper first. While it may be tempting to get a head start on your abstract, you should complete your paper before writing the abstract.
- Review your paper for key points and take notes. One way to take notes is to write one sentence for each paragraph. You should not copy directly from your text since your abstract should have different words and phrases. You do not need to include every detail, and in fact, you should avoid doing so. If you have an outline of your paper, use that as a guide to writing your abstract.
- Give a detailed account of the research methods used in the study and how the results were obtained.
- Provide an account of your findings and what you found as a result of your research.
- If your findings have larger implications, include them in the abstract.
- Condense those main points by summarizing the “who, what, where, and when” of your paper.
- If you don’t have an outline, organize information in the same order as in the paper.
- Write a rough draft of your abstract. Begin your abstract with a clear statement about your thesis and why your readers should care about what you’ve written. Then turn your notes into sentences.
- Avoid using long complicated sentences in your abstract along with ambiguous and unnecessary words and phrases. Remember that your abstract needs to be simple and easy to read.
- Do not include citations or footnotes in your abstract.
- Add transitions to show clear connections between ideas and create a smooth flow to your writing.
- Revise your abstract until it is 5-7 sentences or 250 words or less. Limit the length to one or two paragraphs.
- Proofread your abstract several times to make sure it is free of errors. People will stop reading if they see mistakes, and it will damage your credibility.
Format for an MLA abstract
- Use one-inch margins.
- Double-space the abstract.
- Place the abstract after the title and before the main body of the paper.
- Use one space after punctuation marks.
- Indent the first line of the paragraphs ½ inch from the left margin.
- Use 12-point font such as Times New Roman or Arial.
- Spell out acronyms.
- Include italics instead of quotation marks if you reference a long work in the abstract.
MLA abstract examples
Descriptive abstracts.
- Example 1 on Cannon’s “From Literacy to Literature: Elementary Learning and the Middle English Poet.”
- Example 2 on Sealy-Morris’s “The Rhetoric of the Paneled Page: Comics and Composition Pedagogy.”
Informational abstracts
- Example 1 on O’Neill’s “The Personal Public Sphere of Whitman’s 1840s Journalism.”
Works cited
Cannon, Christopher. “From Literacy to Literature: Elementary Learning and the Middle English Poet.” PMLA , vol. 129, no. 3, 2014, pp. 349–364. JSTOR, www.jstor.org/stable/24769474.
MLA Handbook . 9th ed., Modern Language Association of America, 2021.
O’Neill, Bonnie Carr. “The Personal Public Sphere of Whitman’s 1840s Journalism.” PMLA , vol. 126, no. 4, 2011, pp. 983–998. JSTOR , www.jstor.org/stable/41414171.
Sealey-Morris, Gabriel. “The Rhetoric of the Paneled Page: Comics and Composition Pedagogy.” Composition Studies , vol. 43, no. 1, 2015, pp. 31–50. JSTOR , www.jstor.org/stable/43501877.
Wallace, Joseph. “How to Write an Abstract.” MLA Style Center , Modern Language Association of America, 5 Dec. 2018, style.mla.org/how-to-write-an-abstract/.
Published October 25, 2020. Updated July 18, 2021.
By Catherine Sigler. Catherine has a Ph.D. in English Education
- << Previous: Home
- Next: Annotations >>
- Last Updated: Mar 16, 2023 1:06 PM
- URL: https://libguides.utoledo.edu/abstract
How to Start an Abstract? Examples from 94,745 Research Papers
The examples below are from 94,745 full-text PubMed research papers that I analyzed in order to explore common ways to start writing the Abstract.
Research papers included in this analysis were selected at random from those uploaded to PubMed Central between the years 2016 and 2021. Note that I used the BioC API to download the data (see the References section below).
Examples of how to start writing the Abstract
The Abstract should provide a summary of each section of your paper. It can be divided into subheadings if the journal allows it (refer to the journal’s “Instructions for Authors” ). [for more information, see: How to Write & Publish a Research Paper: Step-by-Step Guide ]
The Abstract can:
1. Start by summarizing the present state of knowledge
For example, here’s the first sentence of the Abstract of a study that wanted to test the 5-year effect of a telephone-based intervention to increase fruit and vegetable consumption in children:
“ Little is known about the long-term impact of telephone-based interventions to improve child diet.” Source: taken from the Abstract of this PubMed article
The beginning of this Abstract emphasizes the lack of previous studies on the topic.
2. Start by demonstrating the importance of the topic
For example, here’s the first sentence of the Abstract of a study on breast cancer testing:
“ Breast cancer is the most commonly diagnosed cancer in women , with 10% of disease attributed to hereditary factors.” Source: taken from the Abstract of this PubMed article
By highlighting the prevalence of breast cancer, the authors showed that the topic of their study is important.
3. Start by showing the gap in previous literature
For example, here’s the first sentence of the Abstract of a study on the incidence of cancer in diabetics treated with metformin:
“ Previous studies evaluating the effect of metformin on cancer risk have been impacted by time-related biases .” Source: taken from the Abstract of this PubMed article
This emphasizes the way the present study fixes problems found in previous literature.
4. Start by mentioning the study objective
In the following example, the authors skipped the small (usually one-line) introduction to the subject and started the Abstract with the study objective:
“ The purpose of this study was to examine the correlation between the foot arch volume measured from static positions and the plantar pressure distribution during walking.” Source: taken from the Abstract of this PubMed article
5. Start with a question
Here’s an example:
“In this article, we address an apparent paradox in the literature on mental time travel and mind-wandering: How is it possible that future thinking is both constructive, yet often experienced as occurring spontaneously? “ Source: taken from the Abstract of this PubMed article
If you want some conflicting opinions on whether or not you should start your Abstract with a question, I suggest the following article on Stack Exchange .
But here’s what the data on 94,745 Abstracts have to say on the subject:
- It is uncommon for an Abstract to start with a question : only 82 (0.09%) of the Abstracts in our sample started with a question.
- On average, starting the Abstract with a question is associated with a lower quality article : the median article whose Abstract start with a question is published in a journal with an impact factor of 2.81 compared to 3.15 for the rest of the articles in the sample.
Common words used to start an Abstract
Here’s a list of the most common words used at the beginning of the Abstract:
- “To investigate the…”
- “To evaluate the…”
- “To assess the…”
- “To determine the…”
- “In this study,…”
- “The present study…”
- “In this paper…”
- “In recent years…”
- “Little is known about…”
- “It is well known that…”
- “This study aimed to…”
- “The present study aimed to…”
- “The aim of this study…”
- “The purpose of this study…”
- “The objective of this study…”
- Comeau DC, Wei CH, Islamaj Doğan R, and Lu Z. PMC text mining subset in BioC: about 3 million full text articles and growing, Bioinformatics , btz070, 2019.
Further reading
- How Long Should the Abstract Be? Data 61,429 from Examples
- How to Write & Publish a Research Paper: Step-by-Step Guide
- Does the Number of Authors Matter? Data from 101,580 Research Papers
- How to Write An Abstract For Research Papers: Tips & Examples
![analyze the sample abstract of the research paper below busayo.longe](https://www.formpl.us/blog/static/dist/img/fpls.png)
In many ways, an abstract is like a trailer of a movie or the synopsis of your favorite book. Its job is to whet the reader’s appetite by sharing important information about your work. After reading a well-written abstract, one should have enough interest to explore the full research thesis.
So how do you write an interesting abstract that captures the core of your study? First, you need to understand your research objectives and match them with the key results of your study. In this article, we will share some tips for writing an effective abstract, plus samples you can learn from.
What is an Abstract in Research Writing?
In simple terms, an abstract is a concise write-up that gives an overview of your systematic investigation. According to Grammarly, it is a self-contained summary of a larger work, and it serves as a preview of the bigger document.
It usually appears at the beginning of your thesis or research paper and helps the reader to have an overview of your work without going into great detail. This means that when someone reads your abstract, it should give them a clear idea of the purpose of your systematic investigation, your problem statement, key results, and any gaps requiring further investigation.
So how long should your abstract be to capture all of these details? The reality is you don’t need a lot of words to capture key pieces of information in your abstract. Typically, 6–7 sentences made up of 150–250 words should be just right.
Read: Writing Research Proposals: Tips, Examples & Mistakes
What are the Characteristics of a Good Abstract?
- A good abstract clearly states the aims and objectives of the research.
- It outlines the research methodology for data gathering , processing and analysis.
- A good abstract summarizes specific research results.
- It states the key conclusions of the systematic investigation.
- It is brief yet straight to the point.
- A good abstract is unified and coherent.
- It is easy to understand and devoid of technical jargon.
- It is written in an unbiased and objective manner.
What is the Purpose of an Abstract?
Every abstract has two major purposes. First, it communicates the relevance of your systematic investigation to readers. After reading your abstract, people can determine how relevant your study is to their primary or secondary research purpose.
The second purpose of an abstract is to communicate your key findings to those who don’t have time to read the whole paper. Research papers typically run into tens of pages so it takes time to read and digest them. To help readers grasp the core ideas in a systematic investigation, it pays to have a well-written abstract that outlines important information concerning your study.
In all, your abstract should accurately outline the most important information in your research. Many times, it determines whether people would go ahead to read your dissertation. Abstracts are often indexed along with keywords on academic databases, so they make your thesis easily findable.
Learn About: How to Write a Problem Statement for your Research
What are the Sections of an Abstract?
You already know the key pieces of information that your abstract should communicate. These details are broken into six important sections of the abstract which are:
- The Introduction or Background
- Research Methodology
- Aims and Objectives
- Limitations
Let’s discuss them in detail.
- The Introduction or Background
The introduction or background is the shortest part of your abstract and usually consists of 2–3 sentences. In fact, some researchers write a single sentence as the introduction of their abstract. The whole idea here is to take the reader through the important events leading to your research.
Understandably, this information may appear difficult to convey in a few sentences. To help out, consider answering these two questions in the background to your study :
- What is already known about the subject, related to the paper in question?
- What is not known about the subject (this is the focus of your study)?
As much as possible, ensure that your abstract’s introduction doesn’t eat into the word count for the other key information.
- Research Methodology
This is the section where you spell out any theories and methods adopted for your study. Ideally, you should cover what has been done and how you went about it to achieve the results of your systematic investigation. It is usually the second-longest section in the abstract.
In the research methodology section, you should also state the type of research you embarked on; that is, qualitative research or quantitative research —this will inform your research methods too. If you’ve conducted quantitative research, your abstract should contain information like the sample size, data collection methods , sampling technique, and duration of your experiment.
Explore: 21 Chrome Extensions for Academic Researchers in 2021
In the end, readers are most interested in the results you’ve achieved with your study. This means you should take time to outline every relevant outcome and show how they affect your research population . Typically, the results section should be the longest one in your abstract and nothing should compromise its range and quality.
An important thing you should do here is spelled out facts and figures about research outcomes. Instead of a vague statement like, “we noticed that response rates differed greatly between high-income and low-income respondents”, try this: “The response rate was higher in high-income respondents than in their low-income counterparts (59% vs 30%, respectively; P
- Conclusion
Like the introduction, your conclusion should contain a few sentences that wrap up your abstract. Most researchers express a theoretical opinion about the implications of their study, here.
Your conclusion should contain three important elements:
- The primary take-home message
- The additional findings of importance
- The perspective
Although the conclusion of your abstract should be short, it has a great impact on how readers perceive your study. So, take advantage of this section to reiterate the core message in your systematic investigation. Also, make sure any statements here reflect the true outcomes and methods of your research.
- Limitations
Chances are you must have faced certain challenges in the course of your research—it could be at the data collection phase or during sampling . Whatever these challenges are, it pays to let your readers know about them, and the impact they had on your study.
For example, if you had to switch to convenience sampling or snowball sampling due to difficulties in contacting well-suited research participants, you should include this in your abstract. Also, a lack of previous studies in the research area could pose a limitation on your study. Research limitations provide an opportunity to make suggestions for further research.
Research aims and objectives speak to what you want to achieve with your study. Typically, research aims focus on a project’s long-term outcomes while the objectives focus on the immediate, short-term outcome of the investigation. You may summarize both using a single paragraph comprising a few sentences.
Stating your aims and objectives will give readers a clear idea of the scope, depth, and direction that your research will ultimately take. Readers would measure your research outcomes against stated aims and objectives to know if you achieved the purpose of your study.
Use For Free: Research Form Templates
Abstract Writing Styles and General Guidelines
Now that you know the different sections plus information that your abstract should contain, let’s look at how to write an abstract for your research paper.
A common question that comes up is, should I write my abstract first or last? It’s best to write your abstract after you’ve finished working on the research because you have full information to present to your readers. However, you can always create a draft at the beginning of your systematic investigation and fill in the gaps later.
Does writing an abstract seem like a herculean task? Here are a few tips to help out.
1. Always create a framework for your abstract
Before you start writing, take time to develop a detailed outline for your abstract. Break it into sections and sketch the main and supporting points for each section. You can list keywords plus 1–2 sentences that capture your core messaging.
2. Read Other Abstracts
Abstracts are one of the most common research documents, and thousands of them have been written in time past. So, before writing yours, try to study a couple of samples from others. You can find lots of dissertation abstract examples in thesis and dissertation databases.
3. Steer Clear of Jargon As Much As Possible
While writing your abstract, emphasize clarity over style. This means you should communicate in simple terms and avoid unnecessary filler words and ambiguous sentences. Remember, your abstract should be understandable to readers who are not familiar with your topic.
4. Focus on Your Research
It goes without saying that your abstract should be solely focused on your research and what you’ve discovered. It’s not the time to cite primary and secondary data sources unless this is absolutely necessary.
This doesn’t mean you should ignore the scholarly background of your work. You might include a sentence or two summarizing the scholarly background to show the relevance of your work to a broader debate, but there’s no need to mention specific publications.
Going further, here are some abstract writing guidelines from the University of Bergen:
- An abstract briefly explains the salient aspects of the content.
- Abstracts should be accurate and succinct, self-contained, and readable.
- The abstract should paraphrase and summarise rather than quote from the paper.
- Abstracts should relate only to the paper to be presented/assessed.
Types of Abstracts with Examples
According to the University of Adelaide, there are two major types of abstracts written for research purposes. First, we have informative abstracts and descriptive abstracts.
1. Informative Abstract
An informative abstract is the more common type of abstract written for academic research. It highlights the most important aspects of your systematic investigation without going into unnecessary or irrelevant details that the reader might not find useful.
The length varies according to discipline, but an informative abstract is rarely more than 10% of the length of the entire work. In the case of longer work, it may be much less.
In any informative abstract, you’d touch on information like the purpose, method, scope, results, and conclusion of your study. By now, you’re thinking, “this is the type of abstract we’ve been discussing all along”, and you wouldn’t be far from the truth.
Advantages of Informative Abstracts
- These abstracts save time for both the researcher and the readers.
- It’s easy to refer to these abstracts as secondary research sources.
Disadvantages of Informative Abstracts
- These types of abstracts lack personality.
Example of an Informative Abstract
- Sample Informative Abstract Based on Experimental Work From Colorado State University
- Sample Informative Abstract Based on Non-experimental Work From Colorado State University
2. Descriptive Abstract
A descriptive abstract reads like a synopsis and focuses on enticing the reader with interesting information. They don’t care as much for data and details, and instead read more like overviews that don’t give too much away.
You’d find descriptive abstracts in artistic criticism pieces and entertainment research as opposed to scientific investigations. This type of abstract makes no judgments about the work, nor does it provide results or conclusions of the research. They are usually written in 100 words or less.
Advantages of Descriptive Abstracts
- It gives a very brief overview of the research paper.
- It is easier to write descriptive abstracts compared to informational abstracts.
Disadvantages of Descriptive Abstracts
- They are suitable for scientific research.
- Descriptive abstracts might omit relevant information that deepens your knowledge of the systematic investigation.
Example of Descriptive Abstracts
- Sample Descriptive Abstract From Colorado State University
FAQs About Writing Abstracts in Research Papers
1. How Long Should an Abstract Be?
A typical abstract should be about six sentences long or less than 150 words. Most universities have specific word count requirements that fall within 150–300 words.
2. How Do You Start an Abstract Sentence?
There are several ways to start your abstract. Consider the following methods:
- State a problem or uncertainty
- Make a general statement with the present research action.
- State the purpose or objective of your research
- State a real-world phenomena or a standard practice.
3. Should you cite in an abstract?
While you can refer to information from specific research papers, there’s no need to cite sources in your abstract. Your abstract should focus on your original research, not on the work of others.
4. What should not be included in an abstract?
An abstract shouldn’t have numeric references, bibliographies, sections, or even footnotes.
5. Which tense is used in writing an abstract?
An abstract should be written in the third-person present tense. Use the simple past tense when describing your methodology and specific findings from your study.
Writing an abstract might appear challenging but with these steps, you should get it right. The easiest approach to writing a good abstract is centering it on key information including your research problem and objectives, methodology, and key results.
![analyze the sample abstract of the research paper below Logo](https://www.formpl.us/static/images/logo/Small-White.png)
Connect to Formplus, Get Started Now - It's Free!
- abstract in research papers
- abstract writing
- descriptive abstract
- good abstract
- purpose of abstract
- qualitative research
- quantitative research
- research methodology
- busayo.longe
![analyze the sample abstract of the research paper below Formplus](https://www.formpl.us/blog/static/dist/img/logo-white.png)
You may also like:
15 Reasons to Choose Quantitative over Qualitative Research
This guide tells you everything you need to know about qualitative and quantitative research, it differences,types, when to use it, how...
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://www.formpl.us/blog/static/dist/img/fpls.png)
How to Write a Problem Statement for your Research
Learn how to write problem statements before commencing any research effort. Learn about its structure and explore examples
Research Questions: Definitions, Types + [Examples]
A comprehensive guide on the definition of research questions, types, importance, good and bad research question examples
Extrapolation in Statistical Research: Definition, Examples, Types, Applications
In this article we’ll look at the different types and characteristics of extrapolation, plus how it contrasts to interpolation.
Formplus - For Seamless Data Collection
Collect data the right way with a versatile data collection tool. try formplus and transform your work productivity today..
How to Write an Abstract?
- Open Access
- First Online: 24 October 2021
Cite this chapter
You have full access to this open access chapter
- Samiran Nundy 4 ,
- Atul Kakar 5 &
- Zulfiqar A. Bhutta 6
60k Accesses
7 Altmetric
An abstract is a crisp, short, powerful, and self-contained summary of a research manuscript used to help the reader swiftly determine the paper’s purpose. Although the abstract is the first paragraph of the manuscript it should be written last when all the other sections have been addressed.
Research is formalized curiosity. It is poking and prying with a purpose. — Zora Neale Hurston, American Author, Anthropologist and Filmmaker (1891–1960)
You have full access to this open access chapter, Download chapter PDF
Similar content being viewed by others
Writing the Abstract
Abstract and Keywords
Additional Commentaries
1 what is an abstract.
An abstract is usually a standalone document that informs the reader about the details of the manuscript to follow. It is like a trailer to a movie, if the trailer is good, it stimulates the audience to watch the movie. The abstract should be written from scratch and not ‘cut –and-pasted’ [ 1 ].
2 What is the History of the Abstract?
An abstract, in the form of a single paragraph, was first published in the Canadian Medical Association Journal in 1960 with the idea that the readers may not have enough time to go through the whole paper, and the first abstract with a defined structure was published in 1991 [ 2 ]. The idea sold and now most original articles and reviews are required to have a structured abstract. The abstract attracts the reader to read the full manuscript [ 3 ].
3 What are the Qualities of a Good Abstract?
The quality of information in an abstract can be summarized by four ‘C’s. It should be:
C: Condensed
C: Critical
4 What are the Types of Abstract?
Before writing the abstract, you need to check with the journal website about which type of abstract it requires, with its length and style in the ‘Instructions to Authors’ section.
The abstract types can be divided into:
Descriptive: Usually written for psychology, social science, and humanities papers. It is about 50–100 words long. No conclusions can be drawn from this abstract as it describes the major points in the paper.
Informative: The majority of abstracts for science-related manuscripts are informative and are surrogates for the research done. They are single paragraphs that provide the reader an overview of the research paper and are about 100–150 words in length. Conclusions can be drawn from the abstracts and in the recommendations written in the last line.
Critical: This type of abstract is lengthy and about 400–500 words. In this, the authors’ own research is discussed for reliability, judgement, and validation. A comparison is also made with similar studies done earlier.
Highlighting: This is rarely used in scientific writing. The style of the abstract is to attract more readers. It is not a balanced or complete overview of the article with which it is published.
Structured: A structured abstract contains information under subheadings like background, aims, material and methods, results, conclusion, and recommendations (Fig. 15.1 ). Most leading journals now carry these.
![analyze the sample abstract of the research paper below figure 1](https://media.springernature.com/lw685/springer-static/image/chp%3A10.1007%2F978-981-16-5248-6_15/MediaObjects/500844_1_En_15_Fig1_HTML.png)
Example of a structured abstract (with permission editor CMRP)
5 What is the Purpose of an Abstract?
An abstract is written to educate the reader about the study that follows and provide an overview of the science behind it. If written well it also attracts more readers to the article. It also helps the article getting indexed. The fate of a paper both before and after publication often depends upon its abstract. Most readers decide if a paper is worth reading on the basis of the abstract. Additionally, the selection of papers in systematic reviews is often dependent upon the abstract.
6 What are the Steps of Writing an Abstract?
An abstract should be written last after all the other sections of an article have been addressed. A poor abstract may turn off the reader and they may cause indexing errors as well. The abstract should state the purpose of the study, the methodology used, and summarize the results and important conclusions. It is usually written in the IMRAD format and is called a structured abstract [ 4 , 5 ].
I: The introduction in the opening line should state the problem you are addressing.
M: Methodology—what method was chosen to finish the experiment?
R: Results—state the important findings of your study.
D: Discussion—discuss why your study is important.
Mention the following information:
Important results with the statistical information ( p values, confidence intervals, standard/mean deviation).
Arrange all information in a chronological order.
Do not repeat any information.
The last line should state the recommendations from your study.
The abstract should be written in the past tense.
7 What are the Things to Be Avoided While Writing an Abstract?
Cut and paste information from the main text
Hold back important information
Use abbreviations
Tables or Figures
Generalized statements
Arguments about the study
![analyze the sample abstract of the research paper below figure a](https://media.springernature.com/lw685/springer-static/image/chp%3A10.1007%2F978-981-16-5248-6_15/MediaObjects/500844_1_En_15_Figa_HTML.png)
8 What are Key Words?
These are important words that are repeated throughout the manuscript and which help in the indexing of a paper. Depending upon the journal 3–10 key words may be required which are indexed with the help of MESH (Medical Subject Heading).
9 How is an Abstract Written for a Conference Different from a Journal Paper?
The basic concept for writing abstracts is the same. However, in a conference abstract occasionally a table or figure is allowed. A word limit is important in both of them. Many of the abstracts which are presented in conferences are never published in fact one study found that only 27% of the abstracts presented in conferences were published in the next five years [ 6 ].
Table 15.1 gives a template for writing an abstract.
10 What are the Important Recommendations of the International Committees of Medical Journal of Editors?
The recommendations are [ 7 ]:
An abstract is required for original articles, metanalysis, and systematic reviews.
A structured abstract is preferred.
The abstract should mention the purpose of the scientific study, how the procedure was carried out, the analysis used, and principal conclusion.
Clinical trials should be reported according to the CONSORT guidelines.
The trials should also mention the funding and the trial number.
The abstract should be accurate as many readers have access only to the abstract.
11 Conclusions
An Abstract should be written last after all the other sections of the manuscript have been completed and with due care and attention to the details.
It should be structured and written in the IMRAD format.
For many readers, the abstract attracts them to go through the complete content of the article.
The abstract is usually followed by key words that help to index the paper.
Andrade C. How to write a good abstract for a scientific paper or conference presentation? Indian J Psychiatry. 2011;53:172–5.
Article Google Scholar
Squires BP. Structured abstracts of original research and review articles. CMAJ. 1990;143:619–22.
CAS PubMed PubMed Central Google Scholar
Pierson DJ. How to write an abstract that will be accepted for presentation at a national meeting. Respir Care. 2004 Oct;49:1206–12.
PubMed Google Scholar
Tenenbein M. The abstract and the academic clinician. Pediatr Emerg Care. 1995;11:40–2.
Article CAS Google Scholar
Bahadoran Z, Mirmiran P, Kashfi K, Ghasemi A. The principles of biomedical scientific writing: abstract and keywords. Int J Endocrinol Metab. 2020;18:e100159.
PubMed PubMed Central Google Scholar
Grover S, Dalton N. Abstract to publication rate: do all the papers presented in conferences see the light of being a full publication? Indian J Psychiatry. 2020;62:73–9.
Preparing a manuscript for submission to a medical journal. Available on http://www.icmje.org/recommendations/browse/manuscript-preparation/preparing-for-submission.html . Accessed 10 May 2020.
Download references
Author information
Authors and affiliations.
Department of Surgical Gastroenterology and Liver Transplantation, Sir Ganga Ram Hospital, New Delhi, India
Samiran Nundy
Department of Internal Medicine, Sir Ganga Ram Hospital, New Delhi, India
Institute for Global Health and Development, The Aga Khan University, South Central Asia, East Africa and United Kingdom, Karachi, Pakistan
Zulfiqar A. Bhutta
You can also search for this author in PubMed Google Scholar
Rights and permissions
Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/ ), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.
The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
Reprints and permissions
Copyright information
© 2022 The Author(s)
About this chapter
Nundy, S., Kakar, A., Bhutta, Z.A. (2022). How to Write an Abstract?. In: How to Practice Academic Medicine and Publish from Developing Countries?. Springer, Singapore. https://doi.org/10.1007/978-981-16-5248-6_15
Download citation
DOI : https://doi.org/10.1007/978-981-16-5248-6_15
Published : 24 October 2021
Publisher Name : Springer, Singapore
Print ISBN : 978-981-16-5247-9
Online ISBN : 978-981-16-5248-6
eBook Packages : Medicine Medicine (R0)
Share this chapter
Anyone you share the following link with will be able to read this content:
Sorry, a shareable link is not currently available for this article.
Provided by the Springer Nature SharedIt content-sharing initiative
- Publish with us
Policies and ethics
- Find a journal
- Track your research
Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.
- View all journals
- Explore content
- About the journal
- Publish with us
- Sign up for alerts
- Open access
- Published: 12 July 2024
The nature of the last universal common ancestor and its impact on the early Earth system
- Edmund R. R. Moody ORCID: orcid.org/0000-0002-8785-5006 1 ,
- Sandra Álvarez-Carretero ORCID: orcid.org/0000-0002-9508-6286 1 ,
- Tara A. Mahendrarajah ORCID: orcid.org/0000-0001-7032-6581 2 ,
- James W. Clark 3 ,
- Holly C. Betts 1 ,
- Nina Dombrowski ORCID: orcid.org/0000-0003-1917-2577 2 ,
- Lénárd L. Szánthó ORCID: orcid.org/0000-0003-3363-2488 4 , 5 , 6 ,
- Richard A. Boyle 7 ,
- Stuart Daines 7 ,
- Xi Chen ORCID: orcid.org/0000-0001-7098-607X 8 ,
- Nick Lane ORCID: orcid.org/0000-0002-5433-3973 9 ,
- Ziheng Yang ORCID: orcid.org/0000-0003-3351-7981 9 ,
- Graham A. Shields ORCID: orcid.org/0000-0002-7828-3966 8 ,
- Gergely J. Szöllősi 5 , 6 , 10 ,
- Anja Spang ORCID: orcid.org/0000-0002-6518-8556 2 , 11 ,
- Davide Pisani ORCID: orcid.org/0000-0003-0949-6682 1 , 12 ,
- Tom A. Williams ORCID: orcid.org/0000-0003-1072-0223 12 ,
- Timothy M. Lenton ORCID: orcid.org/0000-0002-6725-7498 7 &
- Philip C. J. Donoghue ORCID: orcid.org/0000-0003-3116-7463 1
Nature Ecology & Evolution ( 2024 ) Cite this article
52k Accesses
872 Altmetric
Metrics details
- Microbial genetics
- Molecular evolution
- Phylogenetics
The nature of the last universal common ancestor (LUCA), its age and its impact on the Earth system have been the subject of vigorous debate across diverse disciplines, often based on disparate data and methods. Age estimates for LUCA are usually based on the fossil record, varying with every reinterpretation. The nature of LUCA’s metabolism has proven equally contentious, with some attributing all core metabolisms to LUCA, whereas others reconstruct a simpler life form dependent on geochemistry. Here we infer that LUCA lived ~4.2 Ga (4.09–4.33 Ga) through divergence time analysis of pre-LUCA gene duplicates, calibrated using microbial fossils and isotope records under a new cross-bracing implementation. Phylogenetic reconciliation suggests that LUCA had a genome of at least 2.5 Mb (2.49–2.99 Mb), encoding around 2,600 proteins, comparable to modern prokaryotes. Our results suggest LUCA was a prokaryote-grade anaerobic acetogen that possessed an early immune system. Although LUCA is sometimes perceived as living in isolation, we infer LUCA to have been part of an established ecological system. The metabolism of LUCA would have provided a niche for other microbial community members and hydrogen recycling by atmospheric photochemistry could have supported a modestly productive early ecosystem.
Similar content being viewed by others
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://media.springernature.com/w215h120/springer-static/image/art%3A10.1038%2Fs41579-024-01044-y/MediaObjects/41579_2024_1044_Fig1_HTML.png)
Co‐evolution of early Earth environments and microbial life
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://media.springernature.com/w215h120/springer-static/image/art%3A10.1038%2Fs41396-021-00971-5/MediaObjects/41396_2021_971_Fig1_HTML.png)
The curious consistency of carbon biosignatures over billions of years of Earth-life coevolution
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://media.springernature.com/w215h120/springer-static/image/art%3A10.1038%2Fs41598-021-81718-2/MediaObjects/41598_2021_81718_Fig1_HTML.png)
Phanerozoic radiation of ammonia oxidizing bacteria
The common ancestry of all extant cellular life is evidenced by the universal genetic code, machinery for protein synthesis, shared chirality of the almost-universal set of 20 amino acids and use of ATP as a common energy currency 1 . The last universal common ancestor (LUCA) is the node on the tree of life from which the fundamental prokaryotic domains (Archaea and Bacteria) diverge. As such, our understanding of LUCA impacts our understanding of the early evolution of life on Earth. Was LUCA a simple or complex organism? What kind of environment did it inhabit and when? Previous estimates of LUCA are in conflict either due to conceptual disagreement about what LUCA is 2 or as a result of different methodological approaches and data 3 , 4 , 5 , 6 , 7 , 8 , 9 . Published analyses differ in their inferences of LUCA’s genome, from conservative estimates of 80 orthologous proteins 10 up to 1,529 different potential gene families 4 . Interpretations range from little beyond an information-processing and metabolic core 6 through to a prokaryote-grade organism with much of the gene repertoire of modern Archaea and Bacteria 8 , recently reviewed in ref. 7 . Here we use molecular clock methodology, horizontal gene-transfer-aware phylogenetic reconciliation and existing biogeochemical models to address questions about LUCA’s age, gene content, metabolism and impact on the early Earth system.
Estimating the age of LUCA
Life’s evolutionary timescale is typically calibrated to the oldest fossil occurrences. However, the veracity of fossil discoveries from the early Archaean period has been contested 11 , 12 . Relaxed Bayesian node-calibrated molecular clock approaches provide a means of integrating the sparse fossil and geochemical record of early life with the information provided by molecular data; however, constraining LUCA’s age is challenging due to limited prokaryote fossil calibrations and the uncertainty in their placement on the phylogeny. Molecular clock estimates of LUCA 13 , 14 , 15 have relied on conserved universal single-copy marker genes within phylogenies for which LUCA represented the root. Dating the root of a tree is difficult because errors propagate from the tips to the root of the dated phylogeny and information is not available to estimate the rate of evolution for the branch incident on the root node. Therefore, we analysed genes that duplicated before LUCA with two (or more) copies in LUCA’s genome 16 . The root in these gene trees represents this duplication preceding LUCA, whereas LUCA is represented by two descendant nodes. Use of these universal paralogues also has the advantage that the same calibrations can be applied at least twice. After duplication, the same species divergences are represented on both sides of the gene tree 17 , 18 and thus can be assumed to have the same age. This considerably reduces the uncertainty when genetic distance (branch length) is resolved into absolute time and rate. When a shared node is assigned a fossil calibration, such cross-bracing also serves to double the number of calibrations on the phylogeny, improving divergence time estimates. We calibrated our molecular clock analyses using 13 calibrations (see ‘Fossil calibrations’ in Supplementary Information ). The calibration on the root of the tree of life is of particular importance. Some previous studies have placed a younger maximum constraint on the age of LUCA based on the assumption that life could not have survived Late Heavy Bombardment (LHB) (~3.7–3.9 billion years ago (Ga)) 19 . However, the LHB hypothesis is extrapolated and scaled from the Moon’s impact record, the interpretation of which has been questioned in terms of the intensity, duration and even the veracity of an LHB episode 20 , 21 , 22 , 23 . Thus, the LHB hypothesis should not be considered a credible maximum constraint on the age of LUCA. We used soft-uniform bounds, with the maximum-age bound based on the time of the Moon-forming impact (4,510 million years ago (Ma) ± 10 Myr), which would have effectively sterilized Earth’s precursors, Tellus and Theia 13 . Our minimum bound on the age of LUCA is based on low δ 98 Mo isotope values indicative of Mn oxidation compatible with oxygenic photosynthesis and, therefore, total-group Oxyphotobacteria in the Mozaan Group, Pongola Supergroup, South Africa 24 , 25 , dated minimally to 2,954 Ma ± 9 Myr (ref. 26 ).
Our estimates for the age of LUCA are inferred with a concatenated and a partitioned dataset, both consisting of five pre-LUCA paralogues: catalytic and non-catalytic subunits from ATP synthases, elongation factor Tu and G, signal recognition protein and signal recognition particle receptor, tyrosyl-tRNA and tryptophanyl-tRNA synthetases, and leucyl- and valyl-tRNA synthetases 27 . Marginal densities (commonly referred to as effective priors) fall within calibration densities (that is, user-specified priors) when topologically adjacent calibrations do not overlap temporally, but may differ when they overlap, to ensure the relative age relationships between ancestor-descendant nodes. We consider the marginal densities a reasonable interpretation of the calibration evidence given the phylogeny; we are not attempting to test the hypothesis that the fossil record is an accurate temporal archive of evolutionary history because it is not 28 . The duplicated LUCA node age estimates we obtained under the autocorrelated rates (geometric Brownian motion (GBM)) 29 , 30 and independent-rates log-normal (ILN) 31 , 32 relaxed-clock models with our partitioned dataset (GBM, 4.18–4.33 Ga; ILN, 4.09–4.32 Ga; Fig. 1 ) fall within our composite age estimate for LUCA ranging from 3.94 Ga to 4.52 Ga, comparable to previous studies 13 , 18 , 33 . Dating analyses based on single genes, or concatenations that excluded each gene in turn, returned compatible timescales (Extended Data Figs. 1 and 2 and ‘Additional methods’ in Methods ).
![analyze the sample abstract of the research paper below figure 1](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41559-024-02461-1/MediaObjects/41559_2024_2461_Fig1_HTML.png)
Our results suggest that LUCA lived around 4.2 Ga, with a 95% confidence interval spanning 4.09–4.33 Ga under the ILN relaxed-clock model (orange) and 4.18–4.33 Ga under the GBM relaxed-clock model (teal). Under a cross-bracing approach, nodes corresponding to the same species divergences (that is, mirrored nodes) have the same posterior time densities. This figure shows the corresponding posterior time densities of the mirrored nodes for the last universal, archaeal, bacterial and eukaryotic common ancestors (LUCA, LACA, LBCA and LECA, respectively); the last common ancestor of the mitochondrial lineage (Mito-LECA); and the last plastid-bearing common ancestor (LPCA). Purple stars indicate nodes calibrated with fossils. Arc, Archaea; Bac, Bacteria; Euk, Eukarya.
LUCA’s physiology
To estimate the physiology of LUCA, we first inferred an updated microbial phylogeny from 57 phylogenetic marker genes (see ‘Universal marker genes’ in Methods ) on 700 genomes, comprising 350 Archaea and 350 Bacteria 15 . This tree was in good agreement with recent phylogenies of the archaeal and bacterial domains of life 34 , 35 . For example, the TACK 36 and Asgard clades of Archaea 37 , 38 , 39 and Gracilicutes within Bacteria 40 , 41 were recovered as monophyletic. However, the analysis was equivocal as to the phylogenetic placement of the Patescibacteria (CPR) 42 and DPANN 43 , which are two small-genome lineages that have been difficult to place in trees. Approximately unbiased 44 tests could not distinguish the placement of these clades, neither at the root of their respective domains nor in derived positions, with CPR sister to Chloroflexota (as reported recently in refs. 35 , 41 , 45 ) and DPANN sister to Euryarchaeota. To account for this phylogenetic uncertainty, we performed LUCA reconstructions on two trees: our maximum likelihood (ML) tree (topology 1; Extended Data Fig. 3 ) and a tree in which CPR were placed as the sister of Chloroflexota, with DPANN sister to all other Archaea (topology 2; Extended Data Fig. 4 ). In both cases, the gene families mapped to LUCA were very similar (correlation of LUCA presence probabilities (PP), r = 0.6720275, P < 2.2 × 10 − 16 ). We discuss the results on the tree with topology 2 and discuss the residual differences in Supplementary Information , ‘Topology 1’ (Supplementary Data 1 ).
We used the probabilistic gene- and species-tree reconciliation algorithm ALE 46 to infer the evolution of gene family trees for each sampled entry in the KEGG Orthology (KO) database 47 on our species tree. ALE infers the history of gene duplications, transfers and losses based on a comparison between a distribution of bootstrapped gene trees and the reference species tree, allowing us to estimate the probability that the gene family was present at a node in the tree 35 , 48 , 49 . This reconciliation approach has several advantages for drawing inferences about LUCA. Most gene families have experienced gene transfer since the time of LUCA 50 , 51 and so explicitly modelling transfers enables us to include many more gene families in the analysis than has been possible using previous approaches. As the analysis is probabilistic, we can also account for uncertainty in gene family origins and evolutionary history by averaging over different scenarios using the reconciliation model. Using this approach, we estimated the probability that each KEGG gene family (KO) was present in LUCA and then used the resulting probabilities to construct a hypothetical model of LUCA’s gene content, metabolic potential (Fig. 2 ) and environmental context (Fig. 3 ). Using the KEGG annotation is beneficial because it allows us to connect our inferences to curated functional annotations; however, it has the drawback that some widespread gene families that were likely present in LUCA are divided into multiple KO families that individually appear to be restricted to particular taxonomic groups and inferred to have arisen later. To account for this limitation, we also performed an analysis of COG (Clusters of Orthologous Genes) 52 gene families, which correspond to more coarse-grained functional annotations (Supplementary Data 2 ).
![analyze the sample abstract of the research paper below figure 2](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41559-024-02461-1/MediaObjects/41559_2024_2461_Fig2_HTML.png)
In black: enzymes and metabolic pathways inferred to be present in LUCA with at least PP = 0.75, with sampling in both prokaryotic domains. In grey: those inferred in our least-stringent threshold of PP = 0.50. The analysis supports the presence of a complete WLP and an almost complete TCA cycle across multiple confidence thresholds. Metabolic maps derived from KEGG 47 database through iPath 109 . GPI, glycosylphosphatidylinositol; DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane.
![analyze the sample abstract of the research paper below figure 3](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41559-024-02461-1/MediaObjects/41559_2024_2461_Fig3_HTML.png)
a , A representation of LUCA based on our ancestral gene content reconstruction. Gene names in black have been inferred to be present in LUCA under the most-stringent threshold (PP = 0.75, sampled in both domains); those in grey are present at the least-stringent threshold (PP = 0.50, without a requirement for presence in both domains). b , LUCA in the context of the tree of life. Branches on the tree of life that have left sampled descendants today are coloured black, those that have left no sampled descendants are in grey. As the common ancestor of extant cellular life, LUCA is the oldest node that can be reconstructed using phylogenetic methods. It would have shared the early Earth with other lineages (highlighted in teal) that have left no descendants among sampled cellular life today. However, these lineages may have left a trace in modern organisms by transferring genes into the sampled tree of life (red lines) before their extinction. c , LUCA’s chemoautotrophic metabolism probably relied on gas exchange with the immediate environment to achieve organic carbon (C org ) fixation via acetogenesis and it may also have run the metabolism in reverse. d , LUCA within the context of an early ecosystem. The CO 2 and H 2 that fuelled LUCA’s plausibly acetogenic metabolism could have come from both geochemical and biotic inputs. The organic matter and acetate that LUCA produced could have created a niche for other metabolisms, including ones that recycled CO 2 and H 2 (as in modern sediments). e , LUCA in an Earth system context. Acetogenic LUCA could have been a key part of both surface and deep (chemo)autotrophic ecosystems, powered by H 2 . If methanogens were also present, hydrogen would be released as CH 4 to the atmosphere, converted to H 2 by photochemistry and thus recycled back to the surface ecosystem, boosting its productivity. Ferm., fermentation.
Genome size and cellular features
By using modern prokaryotic genomes as training data, we used a predictive model to estimate the genome size and the number of protein families encoded by LUCA based on the relationship between the number of KEGG gene families and the total number of proteins encoded by modern prokaryote genomes (Extended Data Figs. 5 and 6 ). On the basis of the PPs for KEGG KO gene families, we identified a conservative subset of 399 KOs that were likely to be present in LUCA, with PPs ≥0.75, and found in both Archaea and Bacteria (Supplementary Data 1 ); these families form the basis of our metabolic reconstruction. However, by integrating over the inferred PPs of all KO gene families, including those with low probabilities, we also estimate LUCA’s genome size. Our predictive model estimates a genome size of 2.75 Mb (2.49–2.99 Mb) encoding 2,657 (2,451–2,855) proteins ( Methods ). Although we can estimate the number of genes in LUCA’s genome, it is more difficult to identify the specific gene families that might have already been present in LUCA based on the genomes of modern Archaea and Bacteria. It is likely that the modern version of the pathways would be considered incomplete based on LUCA’s gene content through subsequent evolutionary changes. We should therefore expect reconstructions of metabolic pathways to be incomplete due to this phylogenetic noise and other limitations of the analysis pipeline. For example, when looking at genes and pathways that can uncontroversially be mapped to LUCA, such as the ribosome and aminoacyl-tRNA synthetases for implementing the genetic code, we find that we map many (but not all) of the key components to LUCA (see ‘Notes’ in Supplementary Information ). We interpret this to mean that our reconstruction is probably incomplete but our interpretation of LUCA’s metabolism relies on our inference of pathways, not individual genes.
The inferred gene content of LUCA suggests it was an anaerobe as we do not find support for the presence of terminal oxidases (Supplementary Data 1 ). Instead we identified almost all genes encoding proteins of the archaeal (and most of the bacterial) versions of the Wood–Ljungdahl pathway (WLP) (PP > 0.7), indicating that LUCA had the potential for acetogenic growth and/or carbon fixation 53 , 54 , 55 (Supplementary Data 3 ). LUCA encoded some NiFe hydrogenase subunits ( K06281 , PP = 0.90; K14126 , PP = 0.92), which may have enabled growth on hydrogen (see ‘Notes’ in Supplementary Information ). Complexes involved in methanogenesis such as methyl-coenzyme M reductase and tetrahydromethanopterin S-methyltransferase were inferred to be absent, suggesting that LUCA was unlikely to function as a modern methanogen. We found strong support for some components of the TCA cycle (including subunits of oxoglutarate/2-oxoacid ferredoxin oxidoreductase ( K00175 and K00176 ), succinate dehydrogenase ( K00239 ) and homocitrate synthase ( K02594 )), although some steps are missing. LUCA was probably capable of gluconeogenesis/glycolysis in that we find support for most subunits of enzymes involved in these pathways (Supplementary Data 1 and 3 ). Considering the presence of the WLP, this may indicate that LUCA had the ability to grow organoheterotrophically and potentially also autotrophically. Gluconeogenesis would have been important in linking carbon fixation to nucleotide biosynthesis via the pentose phosphate pathway, most enzymes of which seem to be present in LUCA (see ‘Notes’ in Supplementary Information ). We found no evidence that LUCA was photosynthetic, with low PPs for almost all components of oxygenic and anoxygenic photosystems (Supplementary Data 3 ).
We find strong support for the presence of ATP synthase, specifically, the A ( K02117 , PP = 0.98) and B ( K02118 , PP = 0.94) subunit components of the hydrophilic V/A1 subunit, and the I (subunit a, K02123 , PP = 0.99) and K (subunit c, K02124 , PP = 0.82) subunits of the transmembrane V/A0 subunit. In addition, if we relax the sampling threshold, we also infer the presence of the F1-type β-subunit ( K02112 , PP = 0.94). This is consistent with many previous studies that have mapped ATP synthase subunits to LUCA 6 , 17 , 18 , 56 , 57 .
We obtain moderate support for the presence of pathways for assimilatory nitrate (ferredoxin-nitrate reductase, K00367 , PP = 0.69; ferredoxin-nitrite reductase, K00367 , PP = 0.53) and sulfate reduction (sulfate adenylyltransferase, K00957 , PP = 0.80, and K00958 , PP = 0.73; sulfite reductase, K00392 , PP = 0.82; phosphoadenosine phosphosulfate reductase, K00390 , PP = 0.56), probably to fuel amino acid biosynthesis, for which we inferred the presence of 37 partially complete pathways.
We found support for the presence of 19 class 1 CRISPR–Cas effector protein families in the genome of LUCA, including types I and III (cas3, K07012 , PP = 0.80, and K07475 , PP = 0.74; cas10, K07016 , PP = 0.96, and K19076 , PP = 0.67; and cas7, K07061 , PP = 0.90, K09002 , PP = 0.84, K19075 , PP = 0.97, K19115 , PP = 0.98, and K19140 , PP = 0.80). The absence of Cas1 and Cas2 may suggest LUCA encoded an early Cas system with the means to deliver an RNA-based immune response by cutting (Cas6/Cas3) and binding (CSM/Cas10) RNA, but lacking the full immune-system-site CRISPR. This supports the idea that the effector stage of CRISPR–Cas immunity evolved from RNA sensing for signal transduction, based on the similarities in RNA binding modules of the proteins 58 . This is consistent with the idea that cellular life was already involved in an arms race with viruses at the time of LUCA 59 , 60 . Our results indicate that an early Cas system was an ancestral immune system of extant cellular life.
Altogether, our metabolic reconstructions suggest that LUCA was a relatively complex organism, similar to extant Archaea and Bacteria 6 , 7 . On the basis of ancient duplications of the Sec and ATP synthase genes before LUCA, along with high PPs for key components of those systems, membrane-bound ATP synthase subunits, genes involved in peptidoglycan synthesis ( mraY , K01000 ; murC , K01924 ) and the cytoskeletal actin-like protein, MreB ( K03569 ) (Supplementary Data 3 ), it is highly likely that LUCA possessed the core cellular apparatus of modern prokaryotic life. This might include the basic constituents of a phospholipid membrane, although our analysis did not conclusively establish its composition. In particular, we recovered the following enzymes involved in the synthesis of ether and ester lipids, (alkyldihydroxyacetonephosphate synthase, glycerol 3-phosphate and glycerol 1-phosphate) and components of the mevalonate pathway (mevalonate 5-phosphate dehydratase (PP = 0.84), hydroxymethylglutaryl-CoA reductase (PP = 0.52), mevalonate kinase (PP = 0.51) and hydroxymethylglutaryl-CoA synthase (PP = 0.51)).
Compared with previous estimates of LUCA’s gene content, we find 81 overlapping COG gene families with the consensus dataset of ref. 7 and 69 overlapping KOs with the dataset of ref. 6 . Key points of agreement between previous studies include the presence of signal recognition particle protein, ffh (COG0541, K03106 ) 7 used in the targeting and delivery of proteins for the plasma membrane, a high number of aminoacyl-tRNA synthetases for amino acid synthesis and glycolysis/gluconeogenesis enzymes.
Ref. 6 inferred LUCA to be a thermophilic anaerobic autotroph using the WLP for carbon fixation based on the presence of a single enzyme (CODH), and similarly suggested that LUCA was capable of nitrogen fixation using a nitrogenase. Our reconstruction agrees with ref. 6 that LUCA was an anaerobic autotroph using the WLP for carbon fixation, but we infer the presence of a much more complete WLP than that previously obtained. We did not find strong evidence for nitrogenase or nitrogen fixation, and the reconstruction was not definitive with respect to the optimal growth environment of LUCA.
We used a probabilistic approach to reconstruct LUCA—that is, we estimated the probability with which each gene family was present in LUCA based on a model of how gene families evolve along an overarching species tree. This approach differs from analyses of phylogenetic presence–absence profiles 3 , 4 , 9 or those that used filtering criteria (such as broadly distributed or highly vertically evolving families) to define a high-confidence subset of modern genes that might have been present in LUCA. Our reconstruction maps many more genes to LUCA—albeit each with lower probability—than previous analyses 8 and yields an estimate of LUCA’s genome size that is within the range of modern prokaryotes. The result is an incomplete picture of a cellular organism that was prokaryote grade rather than progenotic 2 and that, similarly to prokaryotes today, probably existed as part of an ecosystem. As the common ancestor of sampled, extant prokaryotic life, LUCA is the oldest node on the species tree that we can reconstruct via phylogenomics but, as Fig. 3 illustrates, it was already the product of a highly innovative period in evolutionary history during which most of the core components of cells were established. By definition, we cannot reconstruct LUCA’s contemporaries using phylogenomics but we can propose hypotheses about their physiologies based on the reconstructed LUCA whose features immediately suggest the potential for interactions with other prokaryotic metabolisms.
LUCA’s environment, ecosystem and Earth system context
The inference that LUCA used the WLP helps constrain the environment and ecology in which it could have lived. Modern acetogens can grow autotrophically on H 2 (and CO 2 ) or heterotrophically on a wide range of alternative electron donors including alcohols, sugars and carboxylic acids 55 . This metabolic flexibility is key to their modern ecological success. Acetogenesis, whether autotrophic or heterotrophic, has a low energy yield and growth efficiency (although use of the reductive acetyl-CoA pathway for both energy production and biosynthesis reduces the energy cost of biosynthesis). This would be consistent with an energy-limited early biosphere 61 .
If LUCA functioned as an organoheterotrophic acetogen, it was necessarily part of an ecosystem containing autotrophs providing a source of organic compounds (because the abiotic source flux of organic molecules was minimal on the early Earth). Alternatively, if LUCA functioned as a chemoautotrophic acetogen it could (in principle) have lived independently off an abiotic source of H 2 (and CO 2 ). However, it is implausible that LUCA would have existed in isolation as the by-products of its chemoautotrophic metabolism would have created a niche for a consortium of other metabolisms (as in modern sediments) (Fig. 3d ). This would include the potential for LUCA itself to grow as an organoheterotroph.
A chemoautotrophic acetogenic LUCA could have occupied two major potential habitats (Fig. 3e ): the first is the deep ocean where hydrothermal vents and serpentinization of sea-floor provided a source of H 2 (ref. 62 ). Consistent with this, we find support for the presence of reverse gyrase (PP = 0.97), a hallmark enzyme of hyperthermophilic prokaryotes 6 , 63 , 64 , 65 , which would not be expected if early life existed at the ocean surface (although the evolution of reverse gyrase is complex 63 ; see ‘Reverse gyrase’ in Supplementary Information ). The second habitat is the ocean surface where the atmosphere would have provided a source of H 2 derived from volcanoes and metamorphism. Indeed, we detected the presence of spore photoproduct lyase (COG1533, K03716 , PP = 0.88) that in extant organisms repairs methylene-bridged thymine dimers occurring in spore DNA as a result of damage induced through ultraviolet (UV) radiation 66 , 67 . However, this gene family also occurs in modern taxa that neither form endospores nor dwell in environments where they are likely to accrue UV damage to their DNA and so is not an exclusive hallmark of environments exposed to UV. Previous studies often favoured a deep-ocean environment for LUCA as early life would have been better protected there from an episode of LHB. However, if the LHB was less intense than initially proposed 20 , 22 , or just a sampling artefact 21 , these arguments weaken. Another possibility may be that LUCA inhabited a shallow hydrothermal vent or a hot spring.
Hydrogen fluxes in these ecosystems could have been several times higher on the early Earth (with its greater internal heat source) than today. Volcanism today produces ~1 × 10 12 mol H 2 yr −1 and serpentinization produces ~0.4 × 10 12 mol H 2 yr − 1 . With the present H 2 flux and the known scaling of the H 2 escape rate to space, an abiotic atmospheric concentration of H 2 of ~150 ppmv is predicted 68 . Chemoautotrophic acetogens would have locally drawn down the concentration of H 2 (in either surface or deep niche) but their low growth efficiency would ensure H 2 (and CO 2 ) remained available. This and the organic matter and acetate produced would have created niches for other metabolisms, including methanogenesis (Fig. 3d ).
On the basis of thermodynamic considerations, CH 4 and CO 2 are expected to be the eventual metabolic end products of the resulting ecosystem, with a small fraction of the initial hydrogen consumption buried as organic matter. The resulting flux of CH 4 to the atmosphere would fuel photochemical H 2 regeneration and associated productivity in the surface ocean (Fig. 3e ). Existing models suggest the resulting global H 2 recycling system is highly effective, such that the supply flux of H 2 to the surface could have exceeded the volcanic input of H 2 to the atmosphere by at least an order of magnitude, in turn implying that the productivity of such a biosphere was boosted by a comparable factor 69 . Photochemical recycling to CO would also have supported a surface niche for organisms consuming CO (ref. 69 ).
In deep-ocean habitats, there could be some localized recycling of electrons (Fig. 3d ) but a quantitative loss of highly insoluble H 2 and CH 4 to the atmosphere and minimal return after photochemical conversion of CH 4 to H 2 means global recycling to depth would be minimal (Fig. 3e ). Hence the surface environment for LUCA could have become dominant (albeit recycling of the resulting organic matter could be spread through ocean depth; ‘Deep heterotrophic ecosystem’ in Fig. 3e ). The global net primary productivity of an early chemoautotrophic biosphere including acetogenic LUCA and methanogens could have been of order ~1 × 10 12 to 7 × 10 12 mol C yr − 1 (~3 orders of magnitude less than today) 69 .
The nutrient supply (for example, N) required to support such a biosphere would need to balance that lost in the burial flux of organic matter. Earth surface redox balance dictates that hydrogen loss to space and burial of electrons/hydrogen must together balance input of electrons/hydrogen. Considering contemporary H 2 inputs, and the above estimate of net primary productivity, this suggests a maximum burial flux in the order of ~10 12 mol C yr − 1 , which, with contemporary stoichiometry (C:N ratio of ~7) could demand >10 11 mol N yr − 1 . Lightning would have provided a source of nitrite and nitrate 70 , consistent with LUCA’s inferred pathways of nitrite and (possibly) nitrate reduction. However, it would only have been of the order 3 × 10 9 mol N yr − 1 (ref. 71 ). Instead, in a global hydrogen-recycling system, HCN from photochemistry higher in the atmosphere, deposited and hydrolysed to ammonia in water, would have increased available nitrogen supply by orders of magnitude toward ~3 × 10 12 mol N yr − 1 (refs. 71 , 72 ). This HCN pathway is consistent with the anomalously light nitrogen isotopic composition of the earliest plausible biogenic matter of 3.8–3.7 Ga (ref. 73 ), although that considerably postdates our inferred age of LUCA. These considerations suggest that the proposed LUCA biosphere (Fig. 3e ) would have been energy or hydrogen limited not nitrogen limited.
Conclusions
By treating gene presence probabilistically, our reconstruction maps many more genes (2,657) to LUCA than previous analyses and results in an estimate of LUCA’s genome size (2.75 Mb) that is within the range of modern prokaryotes. The result is a picture of a cellular organism that was prokaryote grade rather than progenotic 2 and that probably existed as a component of an ecosystem, using the WLP for acetogenic growth and carbon fixation. We cannot use phylogenetics to reconstruct other members of this early ecosystem but we can infer their physiologies based on the metabolic inputs and outputs of LUCA. How evolution proceeded from the origin of life to early communities at the time of LUCA remains an open question, but the inferred age of LUCA (~4.2 Ga) compared with the origin of the Earth and Moon suggests that the process required a surprisingly short interval of geologic time.
Universal marker genes
A list of 298 markers were identified by creating a non-redundant list of markers used in previous studies on archaeal and bacterial phylogenies 10 , 35 , 38 , 74 , 75 , 76 , 77 , 78 , 79 . These markers were mapped to the corresponding COG, arCOG and TIGRFAM profile to identify which profile is best suited to extract proteins from taxa of interest. To evaluate whether the markers cover all archaeal and bacterial diversity, proteins from a set of 574 archaeal and 3,020 bacterial genomes were searched against the COG, arCOG and TIGRFAM databases using hmmsearch (v.3.1b2; settings, hmmsearch–tblout output–domtblout–notextw) 52 , 80 , 81 , 82 . Only hits with an e-value less than or equal to 1 × 10 −5 were investigated further and for each protein the best hit was determined based on the e-value (expect value) and bit-score. Results from all database searches were merged based on the protein identifiers and the table was subsetted to only include hits against the 298 markers of interest. On the basis of this table we calculated whether the markers occurred in Archaea, Bacteria or both Archaea and Bacteria. Markers were only included if they were present in at least 50% of taxa and contained less than 10% of duplications, leaving a set of 265 markers. Sequences for each marker were aligned using MAFFT L-INS-i v.7.407 (ref. 83 ) for markers with less than 1,000 sequences or MAFFT 84 for those with more than 1,000 sequences (setting, –reorder) 84 and sequences were trimmed using BMGE 85 , set for amino acids, a BLOcks SUbstitution Matrix 30 similarity matrix, with a entropy score of 0.5 (v.1.12; settings, -t AA -m BLOSUM30 -h 0.5). Single gene trees were generated with IQ-TREE 2 (ref. 86 ), using the LG substitution matrix, with ten-profile mixture models, four CPUs, with 1,000 ultrafast bootstraps optimized by nearest neighbour interchange written to a file retaining branch lengths (v.2.1.2; settings, -m LG + C10 + F + R -nt 4 -wbtl -bb 1,000 -bnni). These single gene trees were investigated for archaeal and bacterial monophyly and the presence of paralogues. Markers that failed these tests were not included in further analyses, leaving a set of 59 markers (3 arCOGs, 46 COGs and 10 TIGRFAMs) suited for phylogenies containing both Archaea and Bacteria (Supplementary Data 4 ).
Marker gene sequence selection
To limit selecting distant paralogues and false positives, we used a bidirectional or reciprocal approach to identify the sequences corresponding to the 59 single-copy markers. In the first inspection (query 1), the 350 archaeal and 350 bacterial reference genomes were queried against all arCOG HMM (hidden Markov model) profiles (All_Arcogs_2018.hmm), all COG HMM profiles (NCBI_COGs_Oct2020.hmm) and all TIGRFAM HMM profiles (TIGRFAMs_15.0_HMM.LIB) using a custom script built on hmmsearch: hmmsearchTable <genomes.faa> <database.hmm> -E 1 × 10 −5 >HMMscan_Output_e5 (HMMER v.3.3.2) 87 . HMM profiles corresponding to the 59 single-copy marker genes (Supplementary Data 4 ) were extracted from each query and the best-hit sequences were identified based on the e-value and bit-score. We used the same custom hmmsearchTable script and conditions (see above) in the second inspection (query 2) to query the best-hit sequences identified above against the full COG HMM database (NCBI_COGs_Oct2020.hmm). Results were parsed and the COG family assigned in query 2 was compared with the COG family assigned to sequences based on the marker gene identity (Supplementary Data 4 ). Sequence hits were validated using the matching COG identifier, resulting in 353 mismatches (that is, COG family in query 1 does not match COG family in query 2) that were removed from the working set of marker gene sequences. These sequences were aligned using MAFFT L-INS-i 83 and then trimmed using BMGE 85 with a BLOSUM30 matrix. Individual gene trees were inferred under ML using IQ-TREE 2 (ref. 86 ) with model fitting, including both the default homologous substitution models and the following complex heterogeneous substitution models (LG substitution matrices with 10–60-profile mixture models, with empirical base frequencies and a discrete gamma model with four categories accounting for rate heterogeneity across sites): LG + C60 + F + G, LG + C50 + F + G, LG + C40 + F + G, LG + C30 + F + G, LG + C20 + F + G and LG + C10 + F + G, with 10,000 ultrafast bootstraps and 10 independent runs to avoid local optima. These 59 gene trees were manually inspected and curated over multiple rounds. Any horizontal gene transfer events, paralogous genes or sequences that violated domain monophyly were removed and two genes (arCOG01561, tuf ; COG0442, ProS ) were dropped at this stage due to the high number of transfer events, resulting in 57 single-copy orthologues for further tree inference.
Species-tree inference
These 57 orthologous sequences were concatenated and ML trees were inferred after three independent runs with IQ-TREE 2 (ref. 86 ) using the same model fitting and bootstrap settings as described above. The tree with the highest log-likelihood of the three runs was chosen as the ML species tree (topology 1). To test the effect of removing the CPR bacteria, we removed all CPR bacteria from the alignment before inferring a species tree (same parameters as above). We also performed approximately unbiased 44 tree topology tests (with IQ-TREE 2 (ref. 86 ), using LG + C20 + F + G) when testing the significance of constraining the species-tree topology (ML tree; Supplementary Fig. 1 ) to have a DPANN clade as sister to all other Archaea (same parameters as above but with a minimally constrained topology with monophyletic Archaea and DPANN sister to other Archaea present in a polytomy (Supplementary Fig. 2 )) and testing a constraint of CPR to be sister to Chloroflexi (Supplementary Fig. 3 ), and a combination of both the DPANN and CPR constraints (topology 2); these were tested against the ML topology, both using the normal 20 amino acid alignments and also with Susko–Roger recoding 88 .
Gene families
For the 700 representative species 15 , gene family clustering was performed using EGGNOGMAPPER v.2 (ref. 89 ), with the following parameters: using the DIAMOND 90 search, a query cover of 50% and an e-value threshold of 0.0000001. Gene families were collated using their KEGG 47 identifier, resulting in 9,365 gene families. These gene families were then aligned using MAFFT 84 v.7.5 with default settings and trimmed using BMGE 85 (with the same settings as above). Five independent sets of ML trees were then inferred using IQ-TREE 2 (ref. 86 ), using LG + F + G, with 1,000 ultrafast bootstrap replicates. We also performed a COG-based clustering analysis in which COGs were assigned based on the modal COG identifier annotated for each KEGG gene family based on the results from EGGNOGMAPPER v.2 (ref. 89 ). These gene families were aligned, trimmed and one set of gene trees (with 1,000 ultrafast bootstrap replicates) was inferred using the same parameters as described above for the KEGG gene families.
Reconciliations
The five sets of bootstrap distributions were converted into ALE files, using ALEobserve, and reconciled against topology 1 and topology 2 using ALEml_undated 91 with the fraction missing for each genome included (where available). Gene family root origination rates were optimized for each COG functional category as previously described 35 and families were categorized into four different groups based on the probability of being present in the LUCA node in the tree. The most-stringent category was that with sampling above 1% in both domains and a PP ≥ 0.75, another category was with PP ≥ 0.75 with no sampling requirement, another with PP ≥ 0.5 with the sampling requirement; the least stringent was PP ≥ 0.5 with no sampling requirement. We used the median probability at the root from across the five runs to avoid potential biases from failed runs in the mean and to account for variation across bootstrap distributions (see Supplementary Fig. 4 for distributions of the inferred ratio of duplications, transfers and losses for all gene families across all tips in the species tree; see Supplementary Data 5 for the inferred duplications, transfers and losses ratios for LUCA, the last bacterial common ancestor and the last archaeal common ancestor).
Metabolic pathway analysis
Metabolic pathways for gene families mapped to the LUCA node were inferred using the KEGG 47 website GUI and metabolic completeness for individual modules was estimated with Anvi’o 92 (anvi-estimate-metabolism), with pathwise completeness.
Additional testing
We tested for the effects of model complexity on reconciliation by using posterior mean site frequency LG + C20 + F + G across three independent runs in comparison with 3 LG + F + G independent runs. We also performed a 10% subsampling of the species trees and gene family alignments across two independent runs for two different subsamples, one with and one without the presence of Asgard archaea. We also tested the likelihood of the gene families under a bacterial root (between Terrabacteria and Gracilicutes) using reconciliations of the gene families under a species-tree topology rooted as such.
Fossil calibrations
On the basis of well-established geological events and the fossil record, we modelled 13 uniform densities to constrain the maximum and minimum ages of various nodes in our phylogeny. We constrained the bounds of the uniform densities to be either hard (no tail probability is allowed after the age constraint) or soft (a 2.5% tail probability is allowed after the age constraint) depending on the interpretation of the fossil record ( Supplementary Information ). Nodes that refer to the same duplication event are identified by MCMCtree as cross-braced (that is, one is chosen as the ‘driver’ node, the rest are ‘mirrored’ nodes). In other words, the sampling during the Markov chain Monte Carlo (MCMC) for cross-braced nodes is not independent: the same posterior time density is inferred for matching mirror–driver nodes (see ‘Additional methods’ for details on our cross-bracing approach).
Timetree inference analyses
Timetree inference with the program MCMCtree (PAML v.4.10.7 (ref. 93 )) proceeded under both the GBM and ILN relaxed-clock models. We specified a vague rate prior with the shape parameter equal to 2 and the scale parameter equal to 2.5: Γ(2, 2.5). This gamma distribution is meant to account for the uncertainty on our estimate for the mean evolutionary rate, ~0.81 substitutions per site per time unit, which we calculated by dividing the tree height of our best-scoring ML tree ( Supplementary Information ) into the estimated mean root age of our phylogeny (that is, 4.520 Ga, time unit = 10 9 years; see ‘Fossil calibrations’ in Supplementary Information for justifications on used calibrations). Given that we are estimating very deep divergences, the molecular clock may be seriously violated. Therefore, we applied a very diffuse gamma prior on the rate variation parameter ( σ 2 ), Γ(1, 10), so that it is centred around σ 2 = 0.1. To incorporate our uncertainty regarding the tree shape, we specified a uniform kernel density for the birth–death sampling process by setting the birth and death processes to 1, λ (per-lineage birth rate) = μ (per-lineage death rate) = 1, and the sampling frequency to ρ (sampling fraction) = 0.1. Our main analysis consisted of inferring the timetree for the partitioned dataset under both the GBM and the ILN relaxed-clock models in which nodes that correspond to the same divergences are cross-braced (that is, hereby referred to as cross-bracing A). In addition, we ran 10 additional inference analyses to benchmark the effect that partitioning, cross-bracing and relaxed-clock models can have on species divergence time estimation: (1) GBM + concatenated alignment + cross-bracing A, (2) GBM + concatenated alignment + cross-bracing B (only nodes that correspond to the same divergences for which there are fossil constraints are cross-braced), (3) GBM + concatenated alignment + without cross-bracing, (4) GBM + partitioned alignment + cross-bracing B, (5) GBM + partitioned alignment + without cross-bracing, (6) ILN + concatenated alignment + cross-bracing A, (7) ILN + concatenated alignment + cross-bracing B, (8) ILN + concatenated alignment + without cross-bracing, (9) ILN + partitioned alignment + cross-bracing B, and (10) ILN + partitioned alignment + without cross-bracing. Lastly, we used (1) individual gene alignments, (2) a leave-one-out strategy (rate prior changed for alignments without ATP and Leu , Γ(2, 2.2), and without Tyr , Γ(2, 2.3), but was Γ(2, 2.5) for the rest; see ‘Additional methods’), and (3) a more complex substitution model 94 to assess their impact on timetree inference. Refer to ‘Additional methods’ for details on how we parsed the dataset we used for timetree inference analyses, ran PAML programs CODEML and MCMCtree to approximate the likelihood calculation 95 , and carried out the MCMC diagnostics for the results obtained under each of the previously mentioned scenarios.
We simulated 100 samples of ‘KEGG genomes’ based on the probabilities of each of the (7,467) gene families being present in LUCA using the random.rand function in numpy 96 . The mean number of KEGG gene families was 1,298.25, the 95% HPD (highest posterior density) minimum was 1,255 and the maximum was 1,340. To infer the relationship between the number of KEGG KO gene families encoded by a genome, the number of proteins and the genome size, we used LOESS (locally estimated scatter-plot smoothing) regression to estimate the relationship between the number of KOs and (1) the number of protein-coding genes and (2) the genome size for the 700 prokaryotic genomes used in the LUCA reconstruction. To ensure that our inference of genome size is robust to uncertainty in the number of paralogues that can be expected to have been present in LUCA, we used the presence of probability for each of these KEGG KO gene families rather than the estimated copy number. We used the predict function to estimate the protein-coding genes and genome size of LUCA using these models and the simulated gene contents encoded with 95% confidence intervals.
Additional methods
Cross-bracing approach implemented in mcmctree.
The PAML program MCMCtree was implemented to allow for the analysis of duplicated genes or proteins so that some nodes in the tree corresponding to the same speciation events in different paralogues share the same age. We used the tree topology depicted in Supplementary Fig. 5 to explain how users can label driver or mirror nodes (more on these terms below) so that the program identifies them as sharing the same speciation events. The tree topology shown in Supplementary Fig. 5 can be written in Newick format as:
(((A1,A2),A3),((B1,B2),B3));
In this example, A and B are paralogues and the corresponding tips labelled as A1–A3 and B1–B3 represent different species. Node r represents a duplication event, whereas other nodes are speciation events. If we want to constrain the same speciation events to have the same age (that is, Supplementary Fig. 5 , see labels a and b (that is, A1–A2 ancestor and B1–B2 ancestor, respectively) and labels v and b (that is, A1–A2–A3 ancestor and B1–B2–B3 ancestor, respectively), we use node labels in the format #1, #2, and so on to identify such nodes:
(((A1, A2) #1, A3) #2, ((B1, B2) [#1 B{0.2, 0.4}], B3) #2) 'B(0.9,1.1)';
Node a and node b are assigned the same label (#1) and so they share the same age ( t ): t a = t b . Similarly, node u and node v have the same age: t u = t v . The former nodes are further constrained by a soft-bound calibration based on the fossil record or geological evidence: 0.2 < t a = t b < 0.4. The latter, however, does not have fossil constraints and thus the only restriction imposed is that both t u and t v are equal. Finally, there is another soft-bound calibration on the root age: 0.9 < t r < 1.1.
Among the nodes on the tree with the same label (for example, those nodes labelled with #1 and those with #2 in our example), one is chosen as the driver node, whereas the others are mirror nodes. If calibration information is provided on one of the shared nodes (for example, nodes a and b in Supplementary Fig. 5 ), the same information therefore applies to all shared nodes. If calibration information is provided on multiple shared nodes, that information has to be the same (for example, you could not constrain node a with a different calibration used to constrain node b in Supplementary Fig. 5 ). The time prior (or the prior on all node ages on the tree) is constructed by using a density at the root of the tree, which is specified by the user (for example, 'B(0.9,1.1)' in our example, which has a minimum of 0.9 and a maximum of 1.1). The ages of all non-calibrated nodes are given by the uniform density. This time prior is similar to that used by ref. 29 . The parameters in the birth–death sampling process ( λ , μ , ρ ; specified using the option BDparas in the control file that executes MCMCtree) are ignored. It is noteworthy that more than two nodes can have the same label but one node cannot have two or more labels. In addition, the prior on rates does not distinguish between speciation and duplication events. The implemented cross-bracing approach can only be enabled if option duplication = 1 is included in the control file. By default, this option is set to 0 and users are not required to include it in the control file (that is, the default option is duplication = 0 ).
Timetree inference
Data parsing.
Eight paralogues were initially selected based on previous work showing a likely duplication event before LUCA: the amino- and carboxy-terminal regions from carbamoyl phosphate synthetase, aspartate and ornithine transcarbamoylases, histidine biosynthesis genes A and F , catalytic and non-catalytic subunits from ATP synthase ( ATP ), elongation factor Tu and G ( EF ), signal recognition protein and signal recognition particle receptor ( SRP ), tyrosyl-tRNA and tryptophanyl-tRNA synthetases ( Tyr ), and leucyl- and valyl-tRNA synthetases ( Leu ) 27 . Gene families were identified using BLASTp 97 . Sequences were downloaded from NCBI 98 , aligned with MUSCLE 99 and trimmed with TrimAl 100 (-strict). Individual gene trees were inferred under the LG + C20 + F + G substitution model implemented in IQ-TREE 2 (ref. 86 ). These trees were manually inspected and curated to remove non-homologous sequences, horizontal gene transfers, exceptionally short or long sequences and extremely long branches. Recent paralogues or taxa of inconsistent and/or uncertain placement inferred with RogueNaRok 101 were also removed. Independent verification of an archaeal or bacterial deep split was achieved using minimal ancestor deviation 102 . This filtering process resulted in the five pairs of paralogous gene families 27 ( ATP , EF , SRP , Tyr and Leu ) that we used to estimate the origination time of LUCA. The alignment used for timetree inference consisted of 246 species, with the majority of taxa having at least two copies (for some eukaryotes, they may be represented by plastid, mitochondrial and nuclear sequences).
To assess the impact that partitioning can have on divergence time estimates, we ran our inference analyses with both a concatenated and a partitioned alignment (that is, gene partitioning scheme). We used PAML v.4.10.7 (programs CODEML and MCMCtree) for all divergence time estimation analyses. Given that a fixed tree topology is required for timetree inference with MCMCtree, we inferred the best-scoring ML tree with IQ-TREE 2 under the LG + C20 + F + G4 (ref. 103 ) model following our previous phylogenetic analyses. We then modified the resulting inferred tree topology following consensus views of species-level relationships 34 , 35 , 104 , which we calibrated with the available fossil calibrations (see below). In addition, we ran three sensitivity tests: timetree inference (1) with each gene alignment separately, (2) under a leave-one-out strategy in which each gene alignment was iteratively removed from the concatenated dataset (for example, remove gene ATP but keep genes EF , Leu , SRP and Tyr concatenated in a unique alignment block; apply the same procedure for each gene family), and (3) using the vector of branch lengths, the gradient vector and the Hessian matrix estimated under a complex substitution model (bsinBV method described in ref. 94 ) with the concatenated dataset used for our core analyses. Four of the gene alignments generated for the leave-one-out strategy had gap-only sequences, these were removed when re-inferring the branch lengths under the LG + C20 + F + G4 model (that is, without ATP , 241 species; without EF , 236 species; without Leu , 243 species; without Tyr , 244 species). We used these trees to set the rate prior used for timetree inference for those alignments not including ATP , EF , Leu or Tyr , respectively. The β value (scale parameter) for the rate prior used when analysing alignments without ATP , Leu and Tyr changed minimally but we updated the corresponding rate priors accordingly (see above). When not including SRP , the alignment did not have any sequences removed (that is, 246 species). All alignments were analysed with the same rate prior, Γ(2, 2.5), except for the three previously mentioned alignments.
Approximating the likelihood calculation during timetree inference using PAML programs
Before timetree inference, we ran the CODEML program to infer the branch lengths of the fixed tree topology, the gradient (first derivative of the likelihood function) and the Hessian matrix (second derivative of the likelihood function); the vectors and matrix are required to approximate the likelihood function in the dating program MCMCtree 95 , an approach that substantially reduces computational time 105 . Given that CODEML does not implement the CAT (Bayesian mixture model for across-site heterogeneity) model, we ran our analyses under the closest available substitution model: LG + F + G4 (model = 3). We calculated the aforementioned vectors and matrix for each of the five gene alignments (that is, required for the partitioned alignment), for the concatenated alignment and for the concatenated alignments used for the leave-one-out strategy; the resulting values are written out in an output file called rst2. We appended the rst2 files generated for each of the five individual alignments in the same order the alignment blocks appear in the partitioned alignment file (for example, the first alignment block corresponds to the ATP gene alignment, and thus the first rst2 block will be the one generated when analysing the ATP gene alignment with CODEML). We named this file in_5parts.BV. There is only one rst2 output file for the concatenated alignments, which we renamed in.BV (main concatenated alignment and concatenated alignments under leave-one-out strategy). When analysing each gene alignment separately, we renamed the rst2 files generated for each gene alignment as in.BV.
MCMC diagnostics
All the chains that we ran with MCMCtree for each type of analysis underwent a protocol of MCMC diagnostics consisting of the following steps: (1) flagging and removal of problematic chains; (2) generating convergence plots before and after chain filtering; (3) using the samples collected by those chains that passed the filters (that is, assumed to have converged to the same target distribution) to summarize the results; (4) assessing chain efficiency and convergence by calculating statistics such as R-hat, tail-ESS and bulk-ESS (in-house wrapper function calling Rstan functions, Rstan v.2.21.7; https://mc-stan.org/rstan/ ); and (5) generating the timetrees for each type of analysis with confidence intervals and high-posterior densities to show the uncertainty surrounding the estimated divergence times. Tail-ESS is a diagnostic tool that we used to assess the sampling efficiency in the tails of the posterior distributions of all estimated divergence times, which corresponds to the minimum of the effective sample sizes for quantiles 2.5% and 97.5%. To assess the sampling efficiency in the bulk of the posterior distributions of all estimated divergence, we used bulk-ESS, which uses rank-normalized draws. Note that if tail-ESS and bulk-ESS values are larger than 100, the chains are assumed to have been efficient and reliable parameter estimates (that is, divergence times in our case). R-hat is a convergence diagnostic measure that we used to compare between- and within-chain divergence time estimates to assess chain mixing. If R-hat values are larger than 1.05, between- and within-chain estimates do not agree and thus mixing has been poor. Lastly, we assessed the impact that truncation may have on the estimated divergence times by running MCMCtree when sampling from the prior (that is, the same settings specified above but without using sequence data, which set the prior distribution to be the target distribution during the MCMC). To summarize the samples collected during this analysis, we carried out the same MCMC diagnostics procedure previously mentioned. Supplementary Fig. 6 shows our calibration densities (commonly referred to as user-specified priors, see justifications for used calibrations above) versus the marginal densities (also known as effective priors) that MCMCtree infers when building the joint prior (that is, a prior built without sequence data that considers age constraints specified by the user, the birth–death with sampling process to infer the time densities for the uncalibrated nodes, the rate priors, and so on). We provide all our results for these quality-control checks in our GitHub repository ( https://github.com/sabifo4/LUCA-divtimes ) and in Extended Data Fig. 1 , Supplementary Figs. 7 – 10 and Supplementary Data 6 . Data, figures and tables used and/or generated following a step-by-step tutorial are detailed in the GitHub repository for each inference analysis.
Additional sensitivity analyses
We compared the divergence times we estimated with the concatenated dataset under the calibration strategy cross-bracing A with those inferred (1) for each gene, (2) for gene alignments analysed under a leave-one-out strategy, and (3) for the main concatenated dataset but when using the vector of branch lengths, the gradient vector and the Hessian matrix estimated under a more complex substitution model 94 . The results are summarized in Extended Data Fig. 2 and Supplementary Data 7 and 8 . The same pattern regarding the calibration densities and marginal densities when the tree topology was pruned (that is, see above for details on the leave-one-out strategy) was observed, and thus no additional figures have been generated. As for our main analyses, the results for these additional sensitivity analyses can be found on our GitHub repository ( https://github.com/sabifo4/LUCA-divtimes ).
Reporting summary
Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.
Data availability
All data required to interpret, verify and extend the research in this article can be found at our figshare repository at https://doi.org/10.6084/m9.figshare.24428659 (ref. 106 ) for the reconciliation and phylogenomic analyses and GitHub at https://github.com/sabifo4/LUCA-divtimes (ref. 107 ) for the molecular clock analyses. Additional data are available at the University of Bristol data repository, data.bris, at https://doi.org/10.5523/bris.405xnm7ei36d2cj65nrirg3ip (ref. 108 ).
Code availability
All code relating to the dating analysis can be found on GitHub at https://github.com/sabifo4/LUCA-divtimes (ref. 107 ), and other custom scripts can be found in our figshare repository at https://doi.org/10.6084/m9.figshare.24428659 (ref. 106 ).
Theobald, D. L. A formal test of the theory of universal common ancestry. Nature 465 , 219–222 (2010).
Article CAS PubMed Google Scholar
Woese, C. R. & Fox, G. E. The concept of cellular evolution. J. Mol. Evol. 10 , 1–6 (1977).
Mirkin, B. G., Fenner, T. I., Galperin, M. Y. & Koonin, E. V. Algorithms for computing parsimonious evolutionary scenarios for genome evolution, the last universal common ancestor and dominance of horizontal gene transfer in the evolution of prokaryotes. BMC Evol. Biol. 3 , 2 (2003).
Article PubMed PubMed Central Google Scholar
Ouzounis, C. A., Kunin, V., Darzentas, N. & Goldovsky, L. A minimal estimate for the gene content of the last universal common ancestor—exobiology from a terrestrial perspective. Res. Microbiol. 157 , 57–68 (2006).
Gogarten, J. P. & Deamer, D. Is LUCA a thermophilic progenote? Nat. Microbiol 1 , 16229 (2016).
Weiss, M. C. et al. The physiology and habitat of the last universal common ancestor. Nat. Microbiol 1 , 16116 (2016).
Crapitto, A. J., Campbell, A., Harris, A. J. & Goldman, A. D. A consensus view of the proteome of the last universal common ancestor. Ecol. Evol. 12 , e8930 (2022).
Kyrpides, N., Overbeek, R. & Ouzounis, C. Universal protein families and the functional content of the last universal common ancestor. J. Mol. Evol. 49 , 413–423 (1999).
Koonin, E. V. Comparative genomics, minimal gene-sets and the last universal common ancestor. Nat. Rev. Microbiol. 1 , 127–136 (2003).
Harris, J. K., Kelley, S. T., Spiegelman, G. B. & Pace, N. R. The genetic core of the universal ancestor. Genome Res. 13 , 407–412 (2003).
Article CAS PubMed PubMed Central Google Scholar
Javaux, E. J. Challenges in evidencing the earliest traces of life. Nature 572 , 451–460 (2019).
Lepot, K. Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon. Earth Sci. Rev. 209 , 103296 (2020).
Article CAS Google Scholar
Betts, H. C. et al. Integrated genomic and fossil evidence illuminates life’s early evolution and eukaryote origin. Nat. Ecol. Evol. 2 , 1556–1562 (2018).
Zhu, Q. et al. Phylogenomics of 10,575 genomes reveals evolutionary proximity between domains Bacteria and Archaea. Nat. Commun. 10 , 5477 (2019).
Moody, E. R. R. et al. An estimate of the deepest branches of the tree of life from ancient vertically evolving genes. eLife 11 , e66695 (2022).
Schwartz, R. M. & Dayhoff, M. O. Origins of prokaryotes, eukaryotes, mitochondria, and chloroplasts. Science 199 , 395–403 (1978).
Shih, P. M. & Matzke, N. J. Primary endosymbiosis events date to the later Proterozoic 994 with cross-calibrated phylogenetic dating of duplicated ATPase proteins. Proc. Natl Acad. Sci. USA 110 , 996 (2013).
Article Google Scholar
Mahendrarajah, T. A. et al. ATP synthase evolution on a cross-braced dated tree of life. Nat. Commun. 14 , 7456 (2023).
Bottke, W. F. & Norman, M. D. The Late Heavy Bombardment. Annu. Rev. Earth Planet. Sci. 45 , 619–647 (2017).
Reimink, J. et al. Quantifying the effect of late bombardment on terrestrial zircons. Earth Planet. Sci. Lett. 604 , 118007 (2023).
Boehnke, P. & Harrison, T. M. Illusory Late Heavy Bombardments. Proc. Natl Acad. Sci. USA 113 , 10802–10806 (2016).
Ryder, G. Mass flux in the ancient Earth–Moon system and benign implications for the origin of life on Earth. J. Geophys. Res. 107 , 6-1–6-13 (2002).
Google Scholar
Hartmann, W. K. History of the terminal cataclysm paradigm: epistemology of a planetary bombardment that never (?) happened. Geosciences 9 , 285 (2019).
Planavsky, N. J. et al. Evidence for oxygenic photosynthesis half a billion years before the great oxidation event. Nat. Geosci. 7 , 283–286 (2014).
Ossa, F. O. et al. Limited oxygen production in the Mesoarchean ocean. Proc. Natl Acad. Sci. USA 116 , 6647–6652 (2019).
Mukasa, S. B., Wilson, A. H. & Young, K. R. Geochronological constraints on the magmatic and tectonic development of the Pongola Supergroup (Central Region), South Africa. Precambrian Res. 224 , 268–286 (2013).
Zhaxybayeva, O., Lapierre, P. & Gogarten, J. P. Ancient gene duplications and the root(s) of the tree of life. Protoplasma 227 , 53–64 (2005).
Article PubMed Google Scholar
Donoghue, P. C. J. & Yang, Z. The evolution of methods for establishing evolutionary timescales. Philos. Trans. R. Soc. Lond. B Biol. Sci. 371 , 3006–3010 (2016).
Thorne, J. L., Kishino, H. & Painter, I. S. Estimating the rate of evolution of the rate of molecular evolution. Mol. Biol. Evol. 15 , 1647–1657 (1998).
Yang, Z. & Rannala, B. Bayesian estimation of species divergence times under a molecular clock using multiple fossil calibrations with soft bounds. Mol. Biol. Evol. 23 , 212–226 (2006).
Rannala, B. & Yang, Z. Inferring speciation times under an episodic molecular clock. Syst. Biol. 56 , 453–466 (2007).
Lemey, P., Rambaut, A., Welch, J. J. & Suchard, M. A. Phylogeography takes a relaxed random walk in continuous space and time. Mol. Biol. Evol. 27 , 1877–1885 (2010).
Craig, J. M., Kumar, S. & Hedges, S. B. The origin of eukaryotes and rise in complexity were synchronous with the rise in oxygen. Front. Bioinform. 3 , 1233281 (2023).
Aouad, M. et al. A divide-and-conquer phylogenomic approach based on character supermatrices resolves early steps in the evolution of the Archaea. BMC Ecol. Evol. 22 , 1 (2022).
Coleman, G. A. et al. A rooted phylogeny resolves early bacterial evolution. Science 372 , eabe0511 (2021).
Guy, L. & Ettema, T. J. G. The archaeal ‘TACK’ superphylum and the origin of eukaryotes. Trends Microbiol. 19 , 580–587 (2011).
Spang, A. et al. Complex Archaea that bridge the gap between prokaryotes and eukaryotes. Nature 521 , 173–179 (2015).
Zaremba-Niedzwiedzka, K. et al. Asgard Archaea illuminate the origin of eukaryotic cellular complexity. Nature 541 , 353–358 (2017).
Eme, L. et al. Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes. Nature 618 , 992–999 (2023).
Raymann, K., Brochier-Armanet, C. & Gribaldo, S. The two-domain tree of life is linked to a new root for the Archaea. Proc. Natl Acad. Sci. USA 112 , 6670–6675 (2015).
Megrian, D., Taib, N., Jaffe, A. L., Banfield, J. F. & Gribaldo, S. Ancient origin and constrained evolution of the division and cell wall gene cluster in Bacteria. Nat. Microbiol. 7 , 2114–2127 (2022).
Brown, C. T. et al. Unusual biology across a group comprising more than 15% of domain Bacteria. Nature 523 , 208–211 (2015).
Rinke, C. et al. Insights into the phylogeny and coding potential of microbial dark matter. Nature 499 , 431–437 (2013).
Shimodaira, H. An approximately unbiased test of phylogenetic tree selection. Syst. Biol. 51 , 492–508 (2002).
Taib, N. et al. Genome-wide analysis of the Firmicutes illuminates the diderm/monoderm transition. Nat. Ecol. Evol. 4 , 1661–1672 (2020).
Szöllõsi, G. J., Rosikiewicz, W., Boussau, B., Tannier, E. & Daubin, V. Efficient exploration of the space of reconciled gene trees. Syst. Biol. 62 , 901–912 (2013).
Kanehisa, M. & Goto, S. KEGG: kyoto encyclopedia of genes and genomes. Nucleic Acids Res. 28 , 27–30 (2000).
Williams, T. A. et al. Integrative modeling of gene and genome evolution roots the archaeal tree of life. Proc. Natl Acad. Sci. USA 114 , E4602–E4611 (2017).
Dharamshi, J. E. et al. Gene gain facilitated endosymbiotic evolution of Chlamydiae. Nat. Microbiol. 8 , 40–54 (2023).
Doolittle, W. F. Phylogenetic classification and the universal tree. Science 284 , 2124–2128 (1999).
Dagan, T. & Martin, W. The tree of one percent. Genome Biol. 7 , 118 (2006).
Tatusov, R. L. et al. The COG database: an updated version includes eukaryotes. BMC Bioinf. 4 , 41 (2003).
Ragsdale, S. W. & Pierce, E. Acetogenesis and the Wood–Ljungdahl pathway of CO 2 fixation. Biochim. Biophys. Acta 1784 , 1873–1898 (2008).
Schuchmann, K. & Müller, V. Autotrophy at the thermodynamic limit of life: a model for energy conservation in acetogenic bacteria. Nat. Rev. Microbiol. 12 , 809–821 (2014).
Schuchmann, K. & Müller, V. Energetics and application of heterotrophy in acetogenic bacteria. Appl. Environ. Microbiol. 82 , 4056–4069 (2016).
Iwabe, N., Kuma, K., Hasegawa, M., Osawa, S. & Miyata, T. Evolutionary relationship of archaebacteria, eubacteria, and eukaryotes inferred from phylogenetic trees of duplicated genes. Proc. Natl Acad. Sci. USA 86 , 9355–9359 (1989).
Gogarten, J. P. et al. Evolution of the vacuolar H + -ATPase: implications for the origin of eukaryotes. Proc. Natl Acad. Sci. USA 86 , 6661–6665 (1989).
Koonin, E. V. & Makarova, K. S. Origins and evolution of CRISPR–Cas systems. Phil. Trans. R. Soc. Lond. B Biol. Sci. 374 , 20180087 (2019).
Krupovic, M., Dolja, V. V. & Koonin, E. V. The LUCA and its complex virome. Nat. Rev. Microbiol. 18 , 661–670 (2020).
Koonin, E. V., Dolja, V. V. & Krupovic, M. The logic of virus evolution. Cell Host Microbe 30 , 917–929 (2022).
Lever, M. A. Acetogenesis in the energy-starved deep biosphere—a paradox? Front. Microbiol. 2 , 284 (2011).
PubMed Google Scholar
Martin, W. & Russell, M. J. On the origin of biochemistry at an alkaline hydrothermal vent. Phil. Trans. R. Soc. Lond. B Biol. Sci. 362 , 1887–1925 (2007).
Catchpole, R. J. & Forterre, P. The evolution of reverse gyrase suggests a nonhyperthermophilic last universal common ancestor. Mol. Biol. Evol. 36 , 2737–2747 (2019).
Groussin, M., Boussau, B., Charles, S., Blanquart, S. & Gouy, M. The molecular signal for the adaptation to cold temperature during early life on Earth. Biol. Lett. 9 , 20130608 (2013).
Boussau, B., Blanquart, S., Necsulea, A., Lartillot, N. & Gouy, M. Parallel adaptations to high temperatures in the Archaean eon. Nature 456 , 942–945 (2008).
Chandor, A. et al. Dinucleotide spore photoproduct, a minimal substrate of the DNA repair spore photoproduct lyase enzyme from Bacillus subtilis. J. Biol. Chem. 281 , 26922–26931 (2006).
Chandra, T. et al. Spore photoproduct lyase catalyzes specific repair of the 5R but not the 5S spore photoproduct. J. Am. Chem. Soc. 131 , 2420–2421 (2009).
Kasting, J. F. The evolution of the prebiotic atmosphere. Orig. Life 14 , 75–82 (1984).
Kharecha, P. A. A Coupled Atmosphere–Ecosystem Model of the Early Archean Biosphere . PhD thesis, Pennsylvania State Univ. (2005).
Barth, P. et al. Isotopic constraints on lightning as a source of fixed nitrogen in Earth’s early biosphere. Nat. Geosci. 16 , 478–484 (2023).
Tian, F., Kasting, J. F. & Zahnle, K. Revisiting HCN formation in Earth’s early atmosphere. Earth Planet. Sci. Lett. 308 , 417–423 (2011).
Zahnle, K. J. Photochemistry of methane and the formation of hydrocyanic acid (HCN) in the Earth’s early atmosphere. J. Geophys. Res. 91 , 2819–2834 (1986).
Stüeken, E. E., Boocock, T., Szilas, K., Mikhail, S. & Gardiner, N. J. Reconstructing nitrogen sources to Earth’s earliest biosphere at 3.7 Ga. Front. Earth Sci. 9 , 675726 (2021).
Ciccarelli, F. D. et al. Toward automatic reconstruction of a highly resolved tree of life. Science 311 , 1283–1287 (2006).
Yutin, N., Makarova, K. S., Mekhedov, S. L., Wolf, Y. I. & Koonin, E. V. The deep archaeal roots of eukaryotes. Mol. Biol. Evol. 25 , 1619–1630 (2008).
Petitjean, C., Deschamps, P., López-García, P. & Moreira, D. Rooting the domain Archaea by phylogenomic analysis supports the foundation of the new kingdom Proteoarchaeota. Genome Biol. Evol. 7 , 191–204 (2014).
Williams, T. A., Cox, C. J., Foster, P. G., Szöllősi, G. J. & Embley, T. M. Phylogenomics provides robust support for a two-domains tree of life. Nat. Ecol. Evol. 4 , 138–147 (2020).
Rinke, C. et al. A standardized archaeal taxonomy for the Genome Taxonomy Database. Nat. Microbiol. 6 , 946–959 (2021).
Parks, D. H. et al. Selection of representative genomes for 24,706 bacterial and archaeal species clusters provide a complete genome-based taxonomy. Preprint at bioRxiv https://doi.org/10.1101/771964 (2019).
Finn, R. D., Clements, J. & Eddy, S. R. HMMER web server: interactive sequence similarity searching. Nucleic Acids Res. 39 , W29–W37 (2011).
Makarova, K. S., Wolf, Y. I. & Koonin, E. V. Archaeal Clusters of Orthologous Genes (arCOGs): an update and application for analysis of shared features between Thermococcales, Methanococcales, and Methanobacteriales. Life 5 , 818–840 (2015).
Haft, D. H., Selengut, J. D. & White, O. The TIGRFAMs database of protein families. Nucleic Acids Res. 31 , 371–373 (2003).
Katoh, K., Kuma, K.-I., Toh, H. & Miyata, T. MAFFT version 5: improvement in accuracy of multiple sequence alignment. Nucleic Acids Res. 33 , 511–518 (2005).
Katoh, K., Misawa, K., Kuma, K.-I. & Miyata, T. MAFFT: a novel method for rapid multiple sequence alignment based on fast Fourier transform. Nucleic Acids Res. 30 , 3059–3066 (2002).
Criscuolo, A. & Gribaldo, S. BMGE (Block Mapping and Gathering with Entropy): a new software for selection of phylogenetic informative regions from multiple sequence alignments. BMC Evol. Biol. 10 , 210 (2010).
Minh, B. Q. et al. IQ-TREE 2: new models and efficient methods for phylogenetic inference in the genomic era. Mol. Biol. Evol. 37 , 1530–1534 (2020).
Eddy, S. R. Accelerated profile HMM searches. PLoS Comput. Biol. 7 , e1002195 (2011).
Susko, E. & Roger, A. J. On reduced amino acid alphabets for phylogenetic inference. Mol. Biol. Evol. 24 , 2139–2150 (2007).
Cantalapiedra, C. P., Hernández-Plaza, A., Letunic, I., Bork, P. & Huerta-Cepas, J. eggNOG-mapper v2: functional annotation, orthology assignments, and domain prediction at the metagenomic scale. Mol. Biol. Evol. 38 , 5825–5829 (2021).
Buchfink, B., Reuter, K. & Drost, H.-G. Sensitive protein alignments at tree-of-life scale using DIAMOND. Nat. Methods 18 , 366–368 (2021).
Szöllősi, G. J., Davín, A. A., Tannier, E., Daubin, V. & Boussau, B. Genome-scale phylogenetic analysis finds extensive gene transfer among fungi. Phil. Trans. R. Soc. Lond. B Biol. Sci. 370 , 20140335 (2015).
Eren, A. M. et al. Community-led, integrated, reproducible multi-omics with anvi’o. Nat. Microbiol. 6 , 3–6 (2021).
Yang, Z. PAML 4: phylogenetic analysis by maximum likelihood. Mol. Biol. Evol. 24 , 1586–1591 (2007).
Wang, S. & Luo, H. Dating the bacterial tree of life based on ancient symbiosis. Preprint at bioRxiv https://doi.org/10.1101/2023.06.18.545440 (2023).
dos Reis, M. & Yang, Z. Approximate likelihood calculation on a phylogeny for Bayesian estimation of divergence times. Mol. Biol. Evol. 28 , 2161–2172 (2011).
Harris et al. Array programming with NumPy. Nature 585 , 357–362 (2020).
Altschul, S. F., Gish, W., Miller, W., Myers, E. W. & Lipman, D. J. Basic local alignment search tool. J. Mol. Biol. 215 , 403–410 (1990).
Sayers, E. W. et al. Database resources of the National Center for Biotechnology Information. Nucleic Acids Res. 39 , D38–D51 (2011).
Edgar, R. C. MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 32 , 1792–1797 (2004).
Capella-Gutiérrez, S., Silla-Martínez, J. M. & Gabaldón, T. trimAl: a tool for automated alignment trimming in large-scale phylogenetic analyses. Bioinformatics 25 , 1972–1973 (2009).
Aberer, A. J., Krompaß, D. & Stamatakis, A. RogueNaRok: An efficient and exact algorithm for rogue taxon identification. Exelixis-RRDR-2011–10 (Heidelberg Institute for Theoretical Studies, 2011).
Tria, F. D. K., Landan, G. & Dagan, T. Phylogenetic rooting using minimal ancestor deviation. Nat. Ecol. Evol. 1 , 193 (2017).
Hoang, D. T., Chernomor, O., von Haeseler, A., Minh, B. Q. & Vinh, L. S. UFBoot2: improving the ultrafast bootstrap approximation. Mol. Biol. Evol. 35 , 518–522 (2018).
Burki, F., Roger, A. J., Brown, M. W. & Simpson, A. G. B. The new tree of eukaryotes. Trends Ecol. Evol. 35 , 43–55 (2020).
Battistuzzi, F. U., Billing-Ross, P., Paliwal, A. & Kumar, S. Fast and slow implementations of relaxed-clock methods show similar patterns of accuracy in estimating divergence times. Mol. Biol. Evol. 28 , 2439–2442 (2011).
Moody, E. R. R. The nature of the last universal common ancestor and its impact on the early Earth system. figshare https://doi.org/10.6084/m9.figshare.24428659 (2024).
Álvarez-Carretero, S. The nature of the last universal common ancestor and its impact on the early Earth system—timetree inference analyses. Zenodo https://doi.org/10.5281/zenodo.11260523 (2024).
Moody, E. R. R. et al. The nature of the Last Universal Common Ancestor and its impact on the early Earth system. Nat. Ecol. Evol. https://doi.org/10.5523/bris.405xnm7ei36d2cj65nrirg3ip (2024).
Darzi, Y., Letunic, I., Bork, P. & Yamada, T. iPath3.0: interactive pathways explorer v3. Nucleic Acids Res. 46 , W510–W513 (2018).
Download references
Acknowledgements
Our research is funded by the John Templeton Foundation (62220 to P.C.J.D., N.L., T.M.L., D.P., G.A.S., T.A.W. and Z.Y.; the opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation), Biotechnology and Biological Sciences Research Council (BB/T012773/1 to P.C.J.D. and Z.Y.; BB/T012951/1 to Z.Y.), by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (947317 ASymbEL to A.S.; 714774, GENECLOCKS to G.J.S.), Leverhulme Trust (RF-2022-167 to P.C.J.D.), Gordon and Betty Moore Foundation (GBMF9741 to T.A.W., D.P., P.C.J.D., A.S. and G.J.S.; GBMF9346 to A.S.), Royal Society (University Research Fellowship (URF) to T.A.W.), the Simons Foundation (735929LPI to A.S.) and the University of Bristol (University Research Fellowship (URF) to D.P.).
Author information
Authors and affiliations.
Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, UK
Edmund R. R. Moody, Sandra Álvarez-Carretero, Holly C. Betts, Davide Pisani & Philip C. J. Donoghue
Department of Marine Microbiology and Biogeochemistry, NIOZ, Royal Netherlands Institute for Sea Research, Den Burg, The Netherlands
Tara A. Mahendrarajah, Nina Dombrowski & Anja Spang
Milner Centre for Evolution, Department of Life Sciences, University of Bath, Bath, UK
James W. Clark
Department of Biological Physics, Eötvös University, Budapest, Hungary
Lénárd L. Szánthó
MTA-ELTE ‘Lendulet’ Evolutionary Genomics Research Group, Budapest, Hungary
Lénárd L. Szánthó & Gergely J. Szöllősi
Institute of Evolution, HUN-REN Center for Ecological Research, Budapest, Hungary
Global Systems Institute, University of Exeter, Exeter, UK
Richard A. Boyle, Stuart Daines & Timothy M. Lenton
Department of Earth Sciences, University College London, London, UK
Xi Chen & Graham A. Shields
Department of Genetics, Evolution and Environment, University College London, London, UK
Nick Lane & Ziheng Yang
Model-Based Evolutionary Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
Gergely J. Szöllősi
Department of Evolutionary & Population Biology, Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, The Netherlands
Bristol Palaeobiology Group, School of Biological Sciences, University of Bristol, Bristol, UK
Davide Pisani & Tom A. Williams
You can also search for this author in PubMed Google Scholar
Contributions
The project was conceived and designed by P.C.J.D., T.M.L., D.P., G.J.S., A.S. and T.A.W. Dating analyses were performed by H.C.B., J.W.C., S.Á.-C., P.J.C.D. and E.R.R.M. T.A.M., N.D. and E.R.R.M. performed single-copy orthologue analysis for species-tree inference. L.L.S., G.J.S., T.A.W. and E.R.R.M. performed reconciliation analysis. E.R.R.M. performed homologous gene family annotation, sequence, alignment, gene tree inference and sensitivity tests. E.R.R.M., A.S. and T.A.W. performed metabolic analysis and interpretation. T.M.L., S.D. and R.A.B. provided biogeochemical interpretation. E.R.R.M., T.M.L., A.S., T.A.W., D.P. and P.J.C.D. drafted the article to which all authors (including X.C., N.L., Z.Y. and G.A.S.) contributed.
Corresponding authors
Correspondence to Edmund R. R. Moody , Davide Pisani , Tom A. Williams , Timothy M. Lenton or Philip C. J. Donoghue .
Ethics declarations
Competing interests.
The authors declare no competing interests.
Peer review
Peer review information.
Nature Ecology & Evolution thanks Aaron Goldman and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data
Extended data fig. 1 comparison of the mean divergence times and confidence intervals estimated for the two duplicates of luca under each timetree inference analysis..
Black dots refer to estimated mean divergence times for analyses without cross-bracing, stars are used to identify those under cross-bracing and triangles for estimated upper and lower confidence intervals. Straight lines are used to link mean divergence time estimates across the various inference analyses we carried out, while dashed lines are used to link the estimated confidence intervals. The node label for the driver node is “248”, while it is “368” for the mirror node, as shown in the title of each graph. Coloured stars and triangles are used to identify which LUCA time estimates were inferred under the same cross-braced analysis for the driver-mirror nodes (that is, equal time and CI estimates). Black dots and triangles are used to identify those inferred when cross-bracing was not enabled (that is, different time and CI estimates). -Abbreviations. “GBM”: Geometric Brownian motion relaxed-clock model; “ILN”: Independent-rate log-normal relaxed-clock model; “conc, cb” dots/triangles: results under cross-bracing A when the concatenated dataset was analysed under GBM (red) and ILN (blue); “conc, fosscb”: results under cross-bracing B when the concatenated dataset was analysed under GBM (orange) and ILN (cyan); “part, cb” dots/triangles: results under cross-bracing A when the partitioned dataset was analysed under GBM (pink) and ILN (purple); “part, fosscb”: results under cross-bracing B when the concatenated dataset was analysed under GBM (light green) and ILN (grey); black dots and triangles: results when cross-bracing was not enabled for both concatenated and partitioned datasets.
Extended Data Fig. 2 Comparison of the posterior time estimates and confidence intervals for the two duplicates of LUCA inferred under the main calibration strategy cross-bracing A with the concatenated dataset and with the datasets for the three additional sensitivity analyses.
Dots refer to estimated mean divergence times and triangles to estimated 2.5% and 97.5% quantiles. Straight lines are used to link the mean divergence times estimated in the same analysis under the two different relaxed-clock models (GBM and ILN). Labels in the x axis are informative about the clock model under which the analysis ran and the type of analysis we carried (see abbreviations below). Coloured dots are used to identify which time estimates were inferred when using the same dataset and strategy under GBM and ILN, while triangles refer to the corresponding upper and lower quantiles for the 95% confidence interval. -Abbreviations. “GBM”: Geometric Brownian motion relaxed-clock model; “ILN”: Independent-rate log-normal relaxed-clock model; “main-conc”: results obtained with the concatenated dataset analysed in our main analyses under cross-bracing A; “ATP/EF/Leu/SRP/Tyr”: results obtained when using each gene alignment separately; “noATP/noEF/noLeu/noSRP/noTyr”: results obtained when using concatenated alignments without the gene alignment mentioned in the label as per the “leave-one-out” strategy; “main-bsinbv”: results obtained with the concatenated dataset analysed in our main analyses when using branch lengths, Hessian, and gradient calculated under a more complex substitution model to infer divergence times.
Extended Data Fig. 3 Maximum Likelihood species tree.
The Maximum Likelihood tree inferred across three independent runs, under the best fitting model (according to BIC: LG + F + G + C60) from a concatenation of 57 orthologous proteins, support values are from 10,000 ultrafast bootstraps. Referred to as topology I in the main text. Tips coloured according to taxonomy: Euryarchaeota (teal), DPANN (purple), Asgardarchaeota (cyan), TACK (blue), Gracilicutes (orange), Terrabacteria (red), DST (brown), CPR (green).
Extended Data Fig. 4 Maximum Likelihood tree for focal reconciliation analysis.
Maximum Likelihood tree (topology II in the main text), where DPANN is constrained to be sister to all other Archaea, and CPR is sister to Chloroflexi. Tips coloured according to taxonomy: Euryarchaeota (teal), DPANN (purple), Asgardarchaeota (cyan), TACK (blue), Gracilicutes (orange), Terrabacteria (red), DST (brown), CPR (green). AU topology test, P = 0.517, this is a one-sided statistical test.
Extended Data Fig. 5 The relationship between the number of KO gene families encoded on a genome and its size.
LOESS regression of the number of KOs per sampled genome against the genome size in megabases. We used the inferred relationship for modern prokaryotes to estimate LUCA’s genome size based on reconstructed KO gene family content, as described in the main text. Shaded area represents the 95% confidence interval.
Extended Data Fig. 6 The relationship between the number of KO gene families encoded on a genome and the total number of protein-coding genes.
LOESS regression of the number of KOs per sampled genome against the number of proteins encoded for per sampled genome. We used the inferred relationship for modern prokaryotes to estimate the total number of protein-coding genes encoded by LUCA based on reconstructed KO gene family content, as described in the main text. Shaded area represents the 95% confidence interval.
Supplementary information
Supplementary information.
Supplementary Notes and Figs. 1–10.
Reporting Summary
Peer review file, supplementary data 1.
This table contains the results of the reconciliations for each gene family. KEGG_ko is the KEGG orthology ID; arc_domain_prop is the proportion of the sampled Archaea; bac_domain_prop is the proportion of the sampled bacteria; gene refers to gene name, description and enzyme code; map refers to the different KEGG maps of which this KEGG gene family is a component; pathway is a text description of the metabolic pathways of which these genes are a component; alignment_length refers to the length of the alignment in amino acids; highest_COG_cat refers to the number of sequences placed in the most frequent COG category; difference_1st_and_2nd is the difference between the most frequent COG category and the second most frequent COG category; categories is the number of different COG categories assigned to this KEGG gene family; COG_freq is the proportion of the sequences placed in the most frequent COG category; COG_cat is the most frequent COG functional category; Archaea is the number of archaeal sequences sampled in the gene family; Bacteria is the number of bacterial sequences sampled in the gene family; alternative_COGs is the number of alternative COG gene families assigned across this KEGG orthologous gene family; COG_perc is the proportion of the most frequent COG ID assigned to this KEGG gene family; COG is the COG ID of the most frequenty COG assigned to this gene family; COG_NAME is the description of the most frequent COG ID assigned to this gene family; COG_TAG is the symbol associated with the most frequent COG gene familiy; sequences is the total number of sequences assigned to this gene family; Arc_prop is the proportion of Archaea that make up this gene family; Bac_prop is the proportion of Bacteria that make up this gene family; constrained_median is the median probability (PP) that this gene was present in LUCA from our reconciliation under the focal constrained tree search across the 5 independent bootstrap distribution reconciliations; ML_median is the median PP of the gene family being present in LUCA with gene tree bootstrap distributions against the ML species-tree topology across the 15 independent bootstrap distribution reconciliations; MEAN_OF_MEDIANS is the mean value across the constrained and ML PP results; RANGE_OF_MEDIANS is the range of the PPs for the constrained and ML topology PPs for LUCA; Probable_and_sampling_threshold_met is our most stringent category of gene families inferred in LUCA with 0.75 + PP and a sampling requirement of 1% met in both Archaea and Bacteria; Possible_and_sampling_threshold_met is a threshold of 0.50 + PP and sampling both domains; probable is simply 0.75 + PP; and possible is 0.50 + PP.
Supplementary Data 2
PP for COGs. This table contains the results for the reconciliations of COG-based gene family clustering against the constrained focal species-tree topology. Columns are named similarly to Supplementary Data 1 but each row is a different COG family. The column Modal_KEGG_ko refers to the most frequent KEGG gene family in which a given COG is found; sequences_in_modal_KEGG refers to the number of sequences in the most frequent KEGG gene family.
Supplementary Data 3
Module completeness. Estimated pathway completeness for KEGG metabolic modules (with a completeness greater than zero in at least one confidence threshold) using Anvi’o’s stepwise pathway completeness 48 . Module_name is the name of the module; module_category is the broader category into which the module falls; module_subcategory is a more specific category; possible_anvio includes the gene families with a median PP ≥ 0.50; probable_anvio related to gene families PP ≥ 0.75; and _ws refers to the sampling requirement being met (presence in at least 1% of the sampled Archaea and Bacteria).
Supplementary Data 4
Marker gene metadata for all markers checked during marker gene curation, including the initial 59 single-copy marker genes used in species-tree inference (see Methods ). Data include marker gene set provenance, marker gene name, marker gene description, presence in different marker gene sets 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , and presence in Archaea and Bacteria. When available, marker genes are matched with their arCOG, TIGR, and COG ID and their respective occurrence across different taxonomic sets is quantified.
Supplementary Data 5
The ratio of duplications, transfers and losses in relation to the total number of copies for the deep ancestral nodes: the LUCA, archaeal (LACA) and bacterial (LBCA) common ancestors, and the average (mean) and 95th percentile.
Supplementary Data 6
Spreadsheet containing a list of the estimated divergence times for all timetree inferences carried out and the corresponding results of the MCMC diagnostics. Tabs Divtimes_GBM-allnodes and Divtimes_ILN-allnodes represent a list of the estimated divergence times (Ma) for all nodes under the 12 inference analyses we ran under GBM and ILN, respectively. Tabs Divtimes_GBM-highlighted and Divtimes_ILN-highlighted represent a list of the estimated divergence times (Ma) for selected nodes ordered according to their mirrored nodes under the 12 inference analyses we ran under GBM and ILN, respectively. Each of the tabs MCMCdiagn_prior, MCMCdiagn_postGBM and MCMCdiagn_postILN contains the statistical results of the MCMC diagnostics we ran for each inference analysis. Note that, despite the analyses carried out when sampling from the prior could have only been done three times (that is, data are not used, and thus only once under each calibration strategy was enough), we repeated them with each dataset regardless. In other words, results for (1) ‘concatenated + cross-bracing A’ and ‘partitioned + cross-bracing A’; (2) ‘concatenated + without cross-bracing’ and ‘partitioned + without cross-bracing’; and (3) ‘concatenated + cross-bracing B’ and ‘partitioned + cross-bracing B’ would be equivalent, respectively. For tabs 1–4, part represents partitioned dataset; conc, concatenated dataset; cb, cross-bracing A; notcb, without cross-bracing; fosscb, cross-bracing B; mean_t, mean posterior time estimate; 2.5%q, 2.5% quantile of the posterior time density for a given node; and 97.5%q, 97.5% quantile of the posterior time density for a given node. For tabs 5–7, med. num. samples collected per chain represents median of the total amount of samples collected per chain; min. num. samples collected per chain, minimum number of samples collected per chain; max. num. samples collected per chain, minimum number of samples collected per chain; num. samples used to calculate stats, number of samples collected by all chains that passed the filters that were used to calculate the tail-ESS, bulk-ESS and R-hat values. For tail-ESS, we report the median, minimum, and maximum tail-ESS values; all larger than 100 as required for assuming reliable parameter estimates. For bulk-ESS, we report the median, minimum and maximum bulk-ESS values; all larger than 100 as required for assuming reliable parameter estimates. For R-hat, minimum and maximum values reported, all smaller than 1.05 as required to assume good mixing.
Supplementary Data 7
Spreadsheet containing a list of the posterior time estimates for LUCA obtained under the main calibration strategy cross-bracing A with the concatenated dataset and with the datasets for the three additional sensitivity analyses. The first column ‘label’ contains the node number for both the driver and mirror nodes for LUCA (the latter includes the term -dup in the label). Columns mean_t, 2.5%q, and 97.5%q refer to the estimated mean divergence times, and the 2.5%/97.5% quantiles of the posterior time density for the corresponding node. Main-conc, refers to results obtained with the concatenated dataset analysed in our main analyses under cross-bracing A; ATP/EF/Leu/SRP/Tyr, results obtained when using each gene alignment separately; noATP/noEF/noLeu/noSRP/noTyr, results obtained when using concatenated alignments without the gene alignment mentioned in the label as per the leave-one-out strategy; main-bsinbv, results obtained with the concatenated dataset analysed in our main analyses when using branch lengths, Hessian and gradient calculated under a more complex substitution model to infer divergence times.
Supplementary Data 8
Spreadsheet containing a list of the estimated divergence times for all timetree inferences carried out for the sensitivity analyses and the corresponding results for the MCMC diagnostics. Tabs Divtimes_GBM-allnodes and Divtimes_ILN-allnodes represent a list of the estimated divergence times (Ma) for all nodes under the 11 inference analyses we ran under GBM and ILN when testing the impact on divergence times estimation when (1) analysing each gene alignment individually, (2) following a leave-one-out strategy, and (3) using the branch lengths, Hessian and gradient estimated under a more complex model for timetree inference (bsinBV approach). Tabs Divtimes_GBM-highlighted and Divtimes_ILN-highlighted represent a list of the estimated divergence times (Ma) for selected nodes ordered according to their mirrored nodes we ran under GBM and ILN for the sensitivity analyses (we also included the results with the main concatenated dataset for reference). Each of tabs MCMCdiagn_prior, MCMCdiagn_postGBM and MCMCdiagn_postILN contains the statistical results of the MCMC diagnostics we ran for the sensitivity analyses. Note that, despite the analyses carried out when sampling from the prior could have only been done once for each different tree topology (that is, data are not used, only topological changes may affect the resulting marginal densities), we ran them with each dataset regardless as part of our pipeline. For tabs 1–4, main-conc represents results obtained with the concatenated dataset analysed in our main analyses under cross-bracing A; ATP/EF/Leu/SRP/Tyr, results obtained when using each gene alignment separately; noATP/noEF/noLeu/noSRP/noTyr, results obtained when using concatenated alignments without the gene alignment mentioned in the label as per the leave-one-out strategy; main-bsinbv, results obtained with the concatenated dataset analysed in our main analyses when using branch lengths, Hessian and gradient calculated under a more complex substitution model to infer divergence times; mean_t, mean posterior time estimate; 2.5%q, 2.5% quantile of the posterior time density for a given node; and 97.5%q, 97.5% quantile of the posterior time density for a given node. For tabs 5–7, med. num. samples collected per chain represents the median of the total amount of samples collected per chain; min. num. samples collected per chain, minimum number of samples collected per chain; max. num. samples collected per chain, minimum number of samples collected per chain; num. samples used to calculate stats, number of samples collected by all chains that passed the filters that were used to calculate the tail-ESS, bulk-ESS and R-hat values. For tail-ESS, we report the median, minimum and maximum tail-ESS values; all larger than 100 as required for assuming reliable parameter estimates. For bulk-ESS, we report the median, minimum and maximum bulk-ESS values; all larger than 100 as required for assuming reliable parameter estimates. For R-hat, minimum and maximum values are reported, all smaller than 1.05 as required to assume good mixing.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ .
Reprints and permissions
About this article
Cite this article.
Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A. et al. The nature of the last universal common ancestor and its impact on the early Earth system. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-024-02461-1
Download citation
Received : 19 January 2024
Accepted : 04 June 2024
Published : 12 July 2024
DOI : https://doi.org/10.1038/s41559-024-02461-1
Share this article
Anyone you share the following link with will be able to read this content:
Sorry, a shareable link is not currently available for this article.
Provided by the Springer Nature SharedIt content-sharing initiative
Quick links
- Explore articles by subject
- Guide to authors
- Editorial policies
Sign up for the Nature Briefing: Microbiology newsletter — what matters in microbiology research, free to your inbox weekly.
![analyze the sample abstract of the research paper below analyze the sample abstract of the research paper below](https://verify.nature.com/verify/nature.png)
To read this content please select one of the options below:
Please note you do not have access to teaching notes, climate change and income inequality in sub-saharan africa (ssa): effects and transmission channels.
International Journal of Development Issues
ISSN : 1446-8956
Article publication date: 5 July 2024
The purpose of this paper is to assess the direct effect of climate change on income inequality in Sub-Saharan Africa (SSA) and the channels through which it spreads.
Design/methodology/approach
Using a sample of 38 countries, the authors specify and estimate a panel data model using the generalized least squares method over the period 1991–2020. Robustness is achieved through the generalized moment method-system.
The results show that an increase in vulnerability to climate change is positively and significantly associated with an increase in income inequality. The results also show that the effects of climate change are mediated by gross domestic product/capita, population and agriculture at the 15%, 17% and 24% thresholds, respectively.
Research limitations/implications
The authors suggest the implementation of inclusive development policies consistent with climate mitigation and adaptation objectives; the creation of financial spaces from various sources to finance the social security of the most vulnerable; and the strengthening of agricultural resilience to climate-related adverse events, including financing for greenhouse agriculture.
Originality/value
On the positive side, it contributes to the literature on the analysis of the direct and indirect effects (transmission channels) of climate change on income inequality in SSA. Methodologically, the study goes beyond previous work as it adopts a stepwise methodology, dealing with the endogeneity issue. At the logical level, it offers some non-exhaustive suggestions of potentially interesting economic policies to guide policymakers in their common commitment to “reduce income inequality” (Sustainable Development Goal 10, target 10.1).
- Income inequality
- Sub-Saharan Africa
- Climate change
Acknowledgements
The authors would like to express the gratitude to the Journal’s editorial team and the anonymous reviewers of the journal.
Funding: The authors received no financial support for the research, authorship and/or publication of this article.
Declaration of conflicting interests: The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article. .
Data availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.
Ewolo Bitoto, F. , Nchinda Mbognou, C. and Amougou Manga, R.J. (2024), "Climate change and income inequality in Sub-Saharan Africa (SSA): effects and transmission channels", International Journal of Development Issues , Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/IJDI-01-2024-0020
Emerald Publishing Limited
Copyright © 2024, Emerald Publishing Limited
Related articles
All feedback is valuable.
Please share your general feedback
Report an issue or find answers to frequently asked questions
Contact Customer Support
Simulation research on blasting of an open pit mine slope considering elevation conditions and slope shape factors
- Wu, Xiaogang
- Zhu, Dayong
- Li, Liangmeng
This study established a numerical model that considers elevation conditions and slope shape factors by the modified Sadovsky formula to analyze the vibration attenuation law of open-pit slopes under blasting vibration conditions. The blasting excavation of a slope in a certain open-pit mine in Yunfu, Guangdong, is selected as an example. Using a numerical model that considers elevation conditions and slope shape factors by the modified Sadovsky formula, a triangular pulse load was utilized to approximate the time-history characteristics of explosion vibration with FLAC3D software. The simulation results showed the radiation range of the blasting vibration seismic wave. By comparison with field monitoring data, the numerical model that considers the slope shape factor had a relative error of ∼10%, while the numerical model that disregards the slope shape factor had a relative error of ∼15%. The relative accuracy of the calculation results of the new numerical model is higher and closer to the actual attenuation law of blasting particle vibration speed, providing more reliable results for slope stability assessment. The peak particle velocities obtained from the numerical simulation results were generally higher than the field monitoring data. These discrepancies might be attributed to the use of simplified models that disregard the discontinuous structural planes within the rock mass. This study provides an important reference for the stability assessment of open-pit slopes under blasting vibration conditions, offering guidance for improving slope stability assessment and related engineering practices.
![](http://cintadecorrer.fun/777/templates/cheerup1/res/banner1.gif)
IMAGES
VIDEO
COMMENTS
Write clearly and concisely. A good abstract is short but impactful, so make sure every word counts. Each sentence should clearly communicate one main point. To keep your abstract or summary short and clear: Avoid passive sentences: Passive constructions are often unnecessarily long.
Choosing Verb Tenses within Your Abstract. The social science sample (Sample 1) below uses the present tense to describe general facts and interpretations that have been and are currently true, including the prevailing explanation for the social phenomenon under study.That abstract also uses the present tense to describe the methods, the findings, the arguments, and the implications of the ...
Follow these five steps to format your abstract in APA Style: Insert a running head (for a professional paper—not needed for a student paper) and page number. Set page margins to 1 inch (2.54 cm). Write "Abstract" (bold and centered) at the top of the page. Place the contents of your abstract on the next line.
Abstracts are usually a student's first point of contact with professional scientific research. Although reading a whole article can be daunting, reading an abstract is much simpler and the benefits to your learning are direct. Here are some ways reading abstracts helps you learn: Finding sources quickly. Gaining knowledge.
5. How to Format an Abstract. Most abstracts use the same formatting rules, which help the reader identify the abstract so they know where to look for it. Here's a list of formatting guidelines for writing an abstract: Stick to one paragraph. Use block formatting with no indentation at the beginning.
Purpose of Research Paper Abstract. The purpose of a research paper abstract is to provide a concise summary of the key points and findings of a research paper. It is typically a brief paragraph or two that appears at the beginning of the paper, before the introduction, and is intended to give readers a quick overview of the paper's content.
The essential elements of an APA abstract are: Running header containing the title of the paper and page number. Section label, centered and in bold, containing the word "abstract". The main content of the abstract, 150-250 words in length and double-spaced. A list of keywords, indented and introduced with the word "keywords" in italics.
Focus on key results, conclusions and take home messages. Write your paper first, then create the abstract as a summary. Check the journal requirements before you write your abstract, eg. required subheadings. Include keywords or phrases to help readers search for your work in indexing databases like PubMed or Google Scholar.
You can, however, write a draft at the beginning of your research and add in any gaps later. If you find abstract writing a herculean task, here are the few tips to help you with it: 1. Always develop a framework to support your abstract. Before writing, ensure you create a clear outline for your abstract.
An abstract is a brief summary which condenses in itself the argument and all the essential information of a paper. An abstract allows the reader to survey the contents of a document quickly and decide whether to continue reading. It needs to be dense with information but also readable, well-organized, brief, and self-contained.
Authors abstract various longer works, including book proposals, dissertations, and online journal articles. There are two main types of abstracts: descriptive and informative. A descriptive abstract briefly describes the longer work, while an informative abstract presents all the main arguments and important results.
An abstract summarizes, usually in one paragraph of 300 words or less, the major aspects of the entire paper in a prescribed sequence that includes: 1) the overall purpose of the study and the research problem(s) you investigated; 2) the basic design of the study; 3) major findings or trends found as a result of your analysis; and, 4) a brief summary of your interpretations and conclusions.
Students are sometimes confused about the difference between an abstract and an introduction. In fact, they are different pieces of writing with different aims and key parts. The following table will briefly describe these differences in the case of a research paper. Abstract Introduction The essence of the whole paper Introduces the paper
To format your abstract: Set one-inch margins on all sides. Label the section "Abstract" on the first line of the page, centered, and using bold font. Use a clear, readable, widely available font, such as Times New Roman (12 pt.) or Calibri (11 pt.). Begin writing the text one line below the "Abstract" label.
Key takeaways . An abstract is a comprehensive summary that presents an overview of your paper. It is presented on a page of its own, and comes after the title page. This page includes a cent er-aligned bold heading 'Abstract' and a short summary (preferably less than 250 words).; An abstract should be concise and precise; it should address the most important details about the paper, for ...
An abstract may contain a succinct background statement highlighting the research's significance, a problem statement, the methodologies used, a synopsis of the results, and the conclusions drawn. When it comes to writing an abstract for a research paper, striking a balance between consciousness and informative detail is essential.
There are six steps to writing a standard abstract. (1) Begin with a broad statement about your topic. Then, (2) state the problem or knowledge gap related to this topic that your study explores. After that, (3) describe what specific aspect of this problem you investigated, and (4) briefly explain how you went about doing this.
Check with your professor to see if an abstract is required for your paper. Different types of abstracts. There are two different types of abstracts: descriptive and informative. Descriptive abstracts are approximately 100 words and give a brief overview of the paper. They do not include a full analysis and may not include the results and/or ...
The examples below are from 94,745 full-text PubMed research papers that I analyzed in order to explore common ways to start writing the Abstract. Research papers included in this analysis were selected at random from those uploaded to PubMed Central between the years 2016 and 2021. ... of the Abstracts in our sample started with a question. On ...
Abstracts are one of the most common research documents, and thousands of them have been written in time past. So, before writing yours, try to study a couple of samples from others. You can find lots of dissertation abstract examples in thesis and dissertation databases. 3. Steer Clear of Jargon As Much As Possible.
publication selected for further reading. An abstract summarises, in one paragraph (usually 200-300 words) that is either unstructured or structured (with sub-headings), the main aspects of an entire research paper/thesis. The best approach is to plan your abstract using the seven points below, and then use these to structure your abstract. 1.
Abstract. An abstract is a crisp, short, powerful, and self-contained summary of a research manuscript used to help the reader swiftly determine the paper's purpose. Although the abstract is the first paragraph of the manuscript it should be written last when all the other sections have been addressed. Research is formalized curiosity.
- The abstract lacks specific details about the methodology used in the study. It does not mention how data was collected or analyzed, which limits the reader's understanding of the research approach. - It also does not provide any findings or conclusions from the study, which could give readers insight into the results of the research. Importance:
Here we infer that LUCA lived ~4.2 Ga (4.09-4.33 Ga) through divergence time analysis of pre-LUCA gene duplicates, calibrated using microbial fossils and isotope records under a new cross ...
The purpose of this paper is to assess the direct effect of climate change on income inequality in Sub-Saharan Africa (SSA) and the channels through which it spreads.,Using a sample of 38 countries, the authors specify and estimate a panel data model using the generalized least squares method over the period 1991-2020.
Paper Context. Main findings: Diabetes is a major, global health threat with rises in incidence projected in low- and middle-income countries, including Ghana, yet evidence gaps remain related to the development of contextually appropriate interventions and policies for diabetes prevention and treatment. Added knowledge: Sitting within a larger, mixed methods study entitled 'Contextual ...
The method employed a three‑dimensional‑printed multi‑well plate and image analysis. Twenty or more replicate peds per soil sample were needed to reliably estimate the sample and treatment means. The multi‑well method improves measurement precision and is practical for research and soil testing laboratories.
The research demonstrates the feasibility of utilizing the X-ray signal generated by irradiation with electrons to identify elements in each sample. It is revealed that employing only the electron beam enables the successful acquisition of quantitative information regarding the sample structure through pyroelectric driven PD-PIXE analysis.
This study established a numerical model that considers elevation conditions and slope shape factors by the modified Sadovsky formula to analyze the vibration attenuation law of open-pit slopes under blasting vibration conditions. The blasting excavation of a slope in a certain open-pit mine in Yunfu, Guangdong, is selected as an example. Using a numerical model that considers elevation ...