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Mouse heaven or mouse hell.

Biologist John Calhoun’s rodent experiments gripped a society consumed by fears of overpopulation.

Officially, the colony was called the Mortality-Inhibiting Environment for Mice. Unofficially, it was called mouse heaven.

Biologist John Calhoun built the colony at the National Institute of Mental Health in Maryland in 1968. It was a large pen—a 4½-foot cube—with everything a mouse could ever desire: plenty of food and water; a perfect climate; reams of paper to make cozy nests; and 256 separate apartments, accessible via mesh tubes bolted to the walls. Calhoun also screened the mice to eliminate disease. Free from predators and other worries, a mouse could theoretically live to an extraordinarily old age there, without a single worry.

But the thing is, this wasn’t Calhoun’s first rodent utopia. This was the 25th iteration. And by this point he knew how quickly mouse heaven could deteriorate into mouse hell.

John Calhoun grew up in Tennessee, the son of a high school principal and an artist, and was an avid birder when young. After earning his PhD in zoology, he joined the Rodent Ecology Project in Baltimore in 1946, whose purpose was to eliminate rodent pests in cities. The project had limited success, partly because no one could figure out what aspects of rodent behavior, lifestyle, or biology to target. Calhoun set up his first utopia, involving Norway rats, in the woods behind his house to monitor rodents over time and figure out what factors drove their population growth.

Eventually Calhoun grew fascinated with the rodent behavior for its own sake and began crafting ever more elaborate and carefully controlled environments. It wasn’t just the behavior of rats that interested him. Architects and civil engineers at the time were having vigorous debates about how to build better cities, and Calhoun imagined urban design might be studied in rodents first and then extrapolated to human beings.

Calhoun’s most famous utopia, number 25, began in July 1968, when he introduced eight albino mice into the 4½-foot cube. Following an adjustment period, the first pups were born 3½ months later, and the population doubled every 55 days afterward. Eventually this torrid growth slowed, but the population continued to climb, peaking at 2,200 mice during the 19th month.

That robust growth masked some serious problems, however. In the wild, infant mortality among mice is high, as most juveniles get eaten by predators or perish of disease or cold. In mouse utopia, juveniles rarely died. As a result, there were far more youngsters than normal, which introduced several difficulties.

Rodents have social hierarchies, with dominant alpha males controlling harems of females. Alphas establish dominance by fighting—wrestling and biting any challengers. Normally a mouse that loses a fight will scurry off to some distant nook to start over elsewhere.

But in mouse utopia, the losing mice couldn’t escape. Calhoun called them “dropouts.” And because so few juveniles died, huge hordes of dropouts would gather in the center of the pen. They were full of cuts and ugly scars, and every so often huge brawls would break out—vicious free-for-alls of biting and clawing that served no obvious purpose. It was just senseless violence. (In earlier utopias involving rats, some dropouts turned to cannibalism.)

Alpha males struggled, too. They kept their harems in private apartments, which they had to defend from challengers. But given how many mice survived to adulthood, there were always a dozen hotshots ready to fight. The alphas soon grew exhausted, and some stopped defending their apartments altogether.

As a result, apartments with nursing females were regularly invaded by rogue males. The mothers fought back, but often to the detriment of their young. Many stressed-out mothers booted their pups from the nest early, before the pups were ready. A few even attacked their own young amid the violence or abandoned them while fleeing to different apartments, leaving the pups to die of neglect.

Eventually other deviant behavior emerged. Mice who had been raised improperly or kicked out of the nest early often failed to develop healthy social bonds, and therefore struggled in adulthood with social interactions. Maladjusted females began isolating themselves like hermits in empty apartments—unusual behavior among mice. Maladjusted males, meanwhile, took to grooming all day—preening and licking themselves hour after hour. Calhoun called them “the beautiful ones.” And yet, even while obsessing over their appearance, these males had zero interest in courting females, zero interest in sex.

Intriguingly, Calhoun had noticed in earlier utopias that such maladjusted behavior could spread like a contagion from mouse to mouse. He dubbed this phenomenon “the behavioral sink.”

Between the lack of sex, which lowered the birth rate, and inability to raise pups properly, which sharply increased infant mortality, the population of Universe 25 began to plummet. By the 21st month, newborn pups rarely survived more than a few days. Soon, new births stopped altogether. Older mice lingered for a while—hiding like hermits or grooming all day—but eventually they died out as well. By spring 1973, less than five years after the experiment started, the population had crashed from 2,200 to 0. Mouse heaven had gone extinct.

Universe 25 ended a half century ago, but it continues to fascinate people today—especially as a gloomy metaphor for human society. Calhoun actively encouraged such speculation, once writing, “I shall largely speak of mice, but my thoughts are on man.” As early as 1968, journalist Tom Wolfe titled an essay about New York “O Rotten Gotham—Sliding Down into the Behavioral Sink.” Oddly, though, none of the prognosticators could agree on the main lesson of Universe 25.

The first people to fret over Universe 25 were environmentalists. The same year the study began, biologist Paul Ehrlich published The Population Bomb , an alarmist book predicting imminent starvation and population crashes due to overpopulation on Earth. Pop culture picked up on this theme in movies, such as Soylent Green , where humans in crowded cities are culled and turned into food slurry. Overall, the idea of dangerous overcrowding was in the air, and some sociologists explicitly drew on Calhoun’s work, writing: “We . . . take the animal studies as a serious model for human populations.” The message was stark: Curb population growth—or else .

More recently scholars saw similarities to the Industrial Revolution and the rise of modern urban society. The 19th and 20th centuries saw population booms across the world, largely due to drops in infant mortality—similar to what the mice experienced. Recently, however, human birth rates have dropped sharply in many developed countries—often below replacement levels—and young people in those places have reportedly lost interest in sex. The parallels to Universe 25 seem spooky.

Behavioral biologists have echoed the eugenics movement in blaming the strange behaviors of the mice on a lack of natural selection, which in their view culls those they consider weak and unfit to breed. This lack of culling resulted in supposed “mutational meltdowns” that led to widespread mouse stupidity and aberrant behavior. (The researchers argued that the brain is especially susceptible to mutations because it’s so intricate and because so many of our genes influence brain function.)

Extrapolating from this work, some political agitators warn that humankind will face a similar decline. Women are supposedly falling into Calhoun’s behavioral sink by learning “maladaptive behaviors,” such as choosing not to have children, which “destroy[s] their own genetic interests.” Other critics agonize over the supposed loss of traditional gender roles, leaving effete males and hyperaggressive females, or they deplore the undermining of religions and their imperatives to “be fruitful and multiply.” In tandem, such changes will lead to the “decline of the West.”

Still others have cast Universe 25’s collapse as a parable illustrating the dangers of socialist welfare states, which, they argue, provide material goods but remove healthy challenges from people’s lives, challenges that build character and promote “personal growth.” Another school of thought viewed Universe 25 as a warning about “the city [as] a perversion of nature.” As sociologists Claude Fischer and Mark Baldassare put it, “A red-eyed, sharp-fanged obsession about urban life stalks contemporary thought.”

Most critics who’ve fretted over Calhoun’s work cluster on the conservative end of the political spectrum, but self-styled progressives have weighed in as well. Advocates for birth control repeatedly invoked Calhoun’s mice as a cautionary tale about how runaway population growth destroys family life. More recent interpretations see the mice collapse in terms of one-percenters and wealth inequality; they blame the social dysfunction on a few aggressive males hoarding precious resources (e.g., desirable apartments). In this view, said one critic, “Universe 25 had a fair distribution problem” above all.

Given these wildly varying (even contradictory) readings, it’s hard to escape the suspicion that personal and political views, rather than objective inquiry, are driving these critics’ outlooks. And indeed, a closer look at the interpretations severely undermines them.

When forecasting population crashes among human beings, Population Bomb –type environmentalists invariably predicted that overcrowding would lead to widespread shortages of food and other goods. That’s actually the opposite of what Universe 25 was like. The mice there had all the goods they wanted. This also undermines arguments about unfair resource distribution.

Perhaps, then, it was the lack of struggles and challenges that led to dysfunction, as welfare critics claimed. Except that the spiral of dysfunction began when hordes of “dropout” mice lost challenges to alpha males, couldn’t escape elsewhere, and began brawling in the middle of the pen. The alpha males in turn grew weary after too many challenges from youngsters. Indeed, most mice faced competition far in excess of what they would encounter in the wild.

The appearance of the sexless “beautiful ones” does seem decadent and echoes the reported loss of interest in sex among young people in developed countries. Except that a closer look at the survey data indicates that such worries might be overblown. And any comparison between human birth rates and Universe 25 birth rates is complicated by the fact that the mouse rates dropped partly due to infant neglect and spikes in infant mortality—the opposite of the situation in the developed world.

Then there are the warnings about the mutational meltdown and the decline of intelligence. Aside from echoing the darkest rhetoric of the eugenics movement, this interpretation runs aground on several points. The hermit females and preening, asexual males certainly acted oddly—but in doing so, they avoided the vicious, violent free-for-alls that beset earlier generations. This hardly seems dumb. Moreover, some of Calhoun’s research actually saw rodents getting smarter during experiments.

This evidence came from an earlier utopia involving rats. In that setup, dropout rats began digging new burrows into the dirt floor of their pen. Digging produces loose dirt to clear away, and most rats laboriously carried the loose dirt outside the tunnel bit by bit, to dump it there. It’s necessary but tedious work.

But some of the dropout rats did something different. Instead of carrying dirt out bit by bit, they packed it all into a ball and rolled it out the tunnel in one trip. An enthused Calhoun compared this innovation to humankind inventing the wheel. And it happened only because the rats were isolated from the main group and didn’t learn the dominant method of digging. By normal rat standards, this was deviant behavior. It was also a creative breakthrough. Overall, then, Calhoun argued that social strife can sometimes push creatures to become smarter, not dumber.

(Incidentally, after Universe 25’s collapse, Calhoun began building new utopias to encourage creative behavior by keeping mice physically and mentally nourished. This research, in turn, inspired a children’s book named after Calhoun’s workplace— Mrs. Frisby and the Rats of NIMH , wherein a group of rats escape from a colony designed to stimulate their intelligence.)

So if all these interpretations of Universe 25 miss the mark, what lesson can we draw from the experiment?

Calhoun’s big takeaway involved status. Again, the males who lost the fights for dominance couldn’t leave to start over elsewhere. As he saw it, they were stuck in pathetic, humiliating roles and lacked a meaningful place in society. The same went for females when they couldn’t nurse or raise pups properly. Both groups became depressed and angry, and began lashing out. In other words, because mice are social animals, they need meaningful social roles to feel fulfilled. Humans are social animals as well, and without a meaningful role, we too can become hostile and lash out.

Still, even this interpretation seems like a stretch. Humans have far more ways of finding meaning in life than pumping out children or dominating some little hierarchy. And while human beings and mice are indeed both social creatures, that common label papers over some major differences. Critics of Calhoun’s work argued that population density among humans—a statistical measure—doesn’t necessarily correlate with crowding —a feeling of psychological stress. In the words of one historian, “Through their intelligence, adaptability, and capacity to make the world around them, humans were capable of coping with crowding” in ways that mice simply are not.

Ultimately Calhoun’s work functions like a Rorschach blot—people see what they want to see. It’s worth remembering that not all lab experiments, especially contrived ones such as Universe 25, apply to the real world. In which case, perhaps the best lesson to learn here is a meta-lesson: that drawing lessons itself can be a dangerous thing.

Sam Kean is a best-selling science author. His latest book is  The Icepick Surgeon: Murder, Fraud, Sabotage, Piracy, and Other Dastardly Deeds Perpetrated in the Name of Science .

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• May 2022, Issue 1
• Foundations

Universe 25 Experiment

A series of rodent experiments showed that even with abundant food and water, personal space is essential to prevent societal collapse, but universe 25's relevance to humans remains disputed..

Stephanie "Annie" Melchor is a freelancer and former intern for The Scientist .

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J une 22, 1972. John Calhoun stood over the abandoned husk of what had once been a thriving metropolis of thousands. Now, the population had dwindled to just 122, and soon, even these inhabitants would be dead. 

Calhoun wasn’t the survivor of a natural disaster or nuclear meltdown; rather, he was a researcher at the National Institute of Mental Health conducting an experiment into the effects of overcrowding on mouse behavior. The results , laid bare at his feet, had taken years to play out.

Universe 25 Experiment Explained

In 1968, Calhoun had started the experiment by introducing four mouse couples into a specially designed pen—a veritable rodent Garden of Eden—with numerous “apartments,” abundant nesting supplies, and unlimited food and water. The only scarce resource in this microcosm was physical space, and Calhoun suspected that it was only a matter of time before this caused trouble in paradise.

Calhoun had been running similar experiments with rodents for decades but had always had to end them prematurely, ironically because of laboratory space constraints, says Edmund Ramsden, a science historian at Queen Mary University of London. This iteration, dubbed Universe 25, was the first crowding experiment he ran to completion.

As he had anticipated, the utopia became hellish nearly a year in when the population density began to peak, and then population growth abruptly and dramatically slowed. Animals became increasingly violent, developed abnormal sexual behaviors, and began neglecting or even attacking their own pups. 

Eventually Universe 25 took another disturbing turn. Mice born into the chaos couldn’t form normal social bonds or engage in complex social behaviors such as courtship, mating, and pup-rearing. Instead of interacting with their peers, males compulsively groomed themselves; females stopped getting pregnant. Effectively, says Ramsden, they became “trapped in an infantile state of early development,” even when removed from Universe 25 and introduced to “normal” mice. Ultimately, the colony died out. “There’s no recovery, and that’s what was so shocking to [Calhoun],” says Ramsden. 

Debunking Popular Interpretations of Universe 25

Calhoun wasn’t shy about anthropomorphizing his findings, binning rodents into categories such as “juvenile delinquents” and “social dropouts,” and others seized on these human parallels. Population growth in the 1970s was swelling, and films such as Soylent Green  tapped into growing fears of overpopulation and urban violence. In a 2011 article , Ramsden writes that Calhoun’s studies were brandished by others to justify population control efforts largely targeted at poor and marginalized communities. 

But Ramsden notes that Calhoun didn’t necessarily think humanity was doomed. In some of Calhoun’s other crowding experiments, rodents developed innovative tunneling behaviors, while in others, adding more rooms allowed the animals to live in the high-density environment without being forced into unwanted contact with others, largely minimizing the negative social consequences. According to Ramsden, Calhoun wanted these findings to influence the architectural design of prisons, mental hospitals, and other buildings prone to crowding. Writing in a report summary in 1979, Calhoun noted that “no single area of intellectual effort can exert a greater influence on human welfare than that contributing to better design of the built environment.” 

Relevance and Criticisms of the Universe 25 Experiment

Looking back on the Universe 25 experiment with present day scientific perspective, the limits of its interpretations are evident. The research was largely observational and subjective. Calhoun described his study as “not normal science,” referring to it instead as an “observation and reconstruction of a process.” 2 Observational studies have a higher risk of bias and confusing correlation with causation. 3 Scientists have suggested that Universe 25 suffers from inaccurate interpretation of experimental outcomes, methods, and potentially confounding variables, 4 which reflect information bias . 3 For instance, at the time that Calhoun presented and published Universe 25’s results, his peers inquired about unsanitary animal husbandry and a lack of quantitative stress hormone measurements as potential confounding or missing information pertinent to Calhoun’s conclusions. 2

Importantly, despite popular interpretations of Universe 25 deeming it informative about urban crowding, many human studies on crowding and population density have yielded inconsistent results. 4 Behavioral scientists today largely acknowledge that how humans experience and respond to crowding is governed by a range of individual-specific social and psychological factors , including personal autonomy and social roles or contexts. 4 In some ways, this aligns with how Calhoun discussed his Universe 25 findings, not as effects of population density per se but effects of altered social interactions . 2 Additionally, the Universe 25 experiment did not address systemic determinants of well-being at the time, nor does it reflect present-day systems that are endemic to the human experience. The societal implications of increased population density and its effects on human beings are a far throw from Universe 25’s experimental design and the behavioral changes that Calhoun observed in his caged rodent experiments. 2,4

Finally, from an ethical standpoint, Calhoun’s experiments would not be permitted today. The mouse universes that Calhoun created intentionally placed its study subjects into constructed environments that caused harm. The study conditions were maintained despite evident animal distress, and many preventable casualties ensued. 2 This goes against current regulatory safety standards for animal research. 5

Which scientist conducted the Universe 25 experiment?

• John B. Calhoun led the Universe 25 experiment , which examined the long-term effects of increasing population density and resulting social stressors on mice living in a constructed environment. 2

How many times was the Universe 25 experiment repeated?

• Universe 25 was one long-term experiment in a series of mouse studies. The entire research series involved Calhoun’s constructed Mortality-Inhibiting Environment for Mice , and each universe examined separate mouse populations and conditions. Calhoun stated that the Universe 25 experiment involved the largest mouse population and longest follow up period. 2

What is a behavioral sink?

• In overcrowding rat studies that Calhoun performed before the Universe 25 experiment, he observed that individual rats began to associate feeding with the company of other rats, which led to the learned behavior of voluntary crowding despite insufficient resources at a crowded site and available resources elsewhere. He termed this specific voluntary crowding a behavioral sink . 1 Calhoun also observed this learned behavior in mice during the Universe 25 experiment. 2

Were the results of the Universe 25 experiment reproduced by other scientists?

• The social effects of population density vary between organisms and populations. Calhoun’s work inspired many scientists to focus on behavioral studies , but the specific experiment has not been replicated. 4,6

What is the criticism of Universe 25?

• The Universe 25 experiment faces several scientific limitations, including experimental biases inherent to observational studies, misinterpretation and unsubstantiated extrapolation to human experiences, and ethical concerns related to animal care . 2-5  

This article was originally published on May 2, 2022, and written by Annie Melchor.

• Calhoun JB. Population density and social pathology . Scientific American Magazine . 1962;206(2):139. 
• Calhoun JB. Death squared: the explosive growth and demise of a mouse population . Proc R Soc Med . 1973;66(1P2):80-88. 
• Boyko EJ. Observational research opportunities and limitations . J Diabetes Complications . 2013;27(6):642-648. 
• Ramsden E. The urban animal: population density and social pathology in rodent and humans . Bull World Health Organ . 2009;87(2):82.
• Animal Research Advisory Committee (ARAC) Guidelines . OACU. Accessed May 28, 2024.
•  Ramsden E, Adams J. Escaping the laboratory: The rodent experiments of John B. Calhoun and their cultural influence . J Soc Hist . 2009;42(3):761-797. 

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All their needs were met, yet it ended in an apocalypse.

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John Calhoun and the mice of the experiment.

Image credit: Yoichi R Okamoto, White House photographer via Wikimedia Commons (public domain)

Over the last few hundred years, the human population of Earth has seen an increase, taking us from an estimated 1 billion in 1804 to 7 billion in 2017. Throughout this time, concerns have been raised that our numbers may outgrow our ability to produce food, leading to widespread famine. 

Some – the Malthusians – even took the view that as resources ran out, the population would "control" itself through mass deaths until a sustainable population was reached. As it happens, advances in farming, changes in farming practices, and new farming technology have given us enough food to feed 10 billion people , and it's how the food is distributed that has caused mass famines and starvation. 

As we use our resources and the climate crisis worsens, this could all change – but for now, we have always been able to produce more food than we need, even if we have lacked the will or ability to distribute it to those that need it.

But while everyone was worried about a lack of resources, one behavioral researcher in the 1970s sought to answer a different question: What happens to society if all our appetites are catered for, and all our needs are met? The answer – according to his study – was an awful lot of cannibalism shortly followed by an apocalypse.

John B Calhoun set about creating a series of experiments that would essentially cater to every need of rodents, and then track the effect on the population over time. The most infamous of the experiments was named, quite dramatically, Universe 25 .

In this study, published in the Proceedings of the Royal Society of Medicine , he took four breeding pairs of mice and placed them inside a "utopia". The environment was designed to eliminate problems that would lead to mortality in the wild. 

They could obtain limitless food via 16 food hoppers, accessed via tunnels, which would feed up to 25 mice at a time, as well as water bottles just above. Nesting material was provided. The weather was kept at 20°C (68°F), which for those of you who aren't mice is the perfect mouse temperature. The mice were chosen for their health, obtained from the National Institutes of Health breeding colony. Extreme precautions were taken to stop any disease from entering the universe.

As well as this, no predators were present in the utopia, which sort of stands to reason. It's not often something is described as a "utopia, but also there were lions there picking us all off one by one". 

The experiment began, and as you'd expect, the mice used the time that would usually be wasted in foraging for food and shelter for having excessive amounts of sexual intercourse. About every 55 days, the population doubled as the mice filled the most desirable space within the pen, where access to the food tunnels was of ease.

When the population hit 620, that slowed to doubling around every 145 days, as the mouse society began to hit problems. The mice split off into groups, and those that could not find a role in these groups found themselves with nowhere to go.

"In the normal course of events in a natural ecological setting somewhat more young survive to maturity than are necessary to replace their dying or senescent established associates," Calhoun wrote in the study. "The excess that find no social niches emigrate."

Here, the "excess" could not emigrate, for there was nowhere else to go. The mice that found themselves with no social role to fill – there are only so many head mouse roles, and the utopia was in no need of a Ratatouille -esque chef – became isolated.

"Males who failed withdrew physically and psychologically; they became very inactive and aggregated in large pools near the centre of the floor of the universe. From this point on they no longer initiated interaction with their established associates, nor did their behavior elicit attack by territorial males," read the paper. "Even so, they became characterized by many wounds and much scar tissue as a result of attacks by other withdrawn males."

The withdrawn males would not respond during attacks, lying there immobile. Later on, they would attack others in the same pattern. The female counterparts of these isolated males withdrew as well. Some mice spent their days preening themselves, shunning mating, and never engaging in fighting. Due to this they had excellent fur coats, and were dubbed, somewhat disconcertingly, the "beautiful ones".

The breakdown of usual mouse behavior wasn't just limited to the outsiders. The " alpha male " mice became extremely aggressive, attacking others with no motivation or gain for themselves, and regularly raped both males and females . Violent encounters sometimes ended in mouse-on-mouse cannibalism.

Despite – or perhaps because of – the fact their every need was being catered for, mothers would abandon their young or merely just forget about them entirely, leaving them to fend for themselves. The mother mice also became aggressive towards trespassers to their nests, with males that would normally fill this role banished to other parts of the utopia. This aggression spilled over, and the mothers would regularly kill their young. Infant mortality in some territories of the utopia reached 90 percent.

This was all during the first phase of the downfall of the "utopia". In the phase Calhoun termed the "second death", whichever young mice survived the attacks from their mothers and others would grow up around these unusual mouse behaviors. As a result, they never learned usual mouse behaviors and many showed little or no interest in mating, preferring to eat and preen themselves, alone.

The population peaked at 2,200 – short of the actual 3,000-mouse capacity of the "universe" – and from there came the decline. Many of the mice weren't interested in breeding and retired to the upper decks of the enclosure, while the others formed into violent gangs below, which would regularly attack and cannibalize other groups as well as their own. The low birth rate and high infant mortality combined with the violence, and soon the entire colony was extinct. During the mousepocalypse, food remained ample, and their every need completely met.

Calhoun termed what he saw as the cause of the collapse "behavioral sink".

"For an animal so simple as a mouse, the most complex behaviours involve the interrelated set of courtship, maternal care, territorial defence and hierarchical intragroup and intergroup social organization," he concluded in his study.

"When behaviours related to these functions fail to mature, there is no development of social organization and no reproduction. As in the case of my study reported above, all members of the population will age and eventually die. The species will die out."

He believed that the mouse experiment may also apply to humans , and warned of a day when – god forbid – all our needs are met.

"For an animal so complex as man, there is no logical reason why a comparable sequence of events should not also lead to species extinction. If opportunities for role fulfilment fall far short of the demand by those capable of filling roles, and having expectancies to do so, only violence and disruption of social organization can follow."

At the time, the experiment and conclusion became quite popular, resonating with people's feelings about overcrowding in urban areas leading to "moral decay" (though of course, this ignores so many factors, such as poverty and prejudice).

However, in recent times, people have questioned whether the experiment could really be applied so simply to humans – and whether it really showed what we believed it did in the first place.

The end of the mouse utopia could have arisen "not from density, but from excessive social interaction," medical historian Edmund Ramsden told the NIH Record, according to  Smithsonian Magazine . “Not all of Calhoun’s rats [which he also experimented on] had gone berserk. Those who managed to control space led relatively normal lives.”

As well as this, the experiment design has been criticized for creating not an overpopulation problem, but rather a scenario where the more aggressive mice were able to control the territory and isolate everyone else. Much like with food production in the real world, it's possible that the problem wasn't of adequate resources, but how those resources are controlled.

An earlier version of this article was published in July 2021 .

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Universe 25 'Rodent Utopia' Experiment Doesn't Mean Human Society Is Dying

John calhoun's "rodent utopia" experiments have been frequently used as evidence for "societal decay.", published may 21, 2024.

The closest thing to utopia the world has ever seen might have existed in a Maryland barn for a couple of years during the late 1960s: a complex built for rodents as part of a science experiment.

The study had an interesting premise and shocking results — a failed society that pushed itself into extinction. Almost immediately, scientists and laypeople alike began suggesting it could be apocalyptic prediction of the future of humanity. In other words, it was almost tailor-made for internet virality.

Snopes readers have written many emails over the last few years asking us about the notorious rodent utopia experiment, sometimes called "Universe 25."

The Background

Before explaining the experiment, it's important to understand why it   was performed. While environmentalism as a political theory had been around in bits and pieces since the early days of the Industrial Revolution, it was not until just after World War II that people truly began to politically organize around the environment.

One of the largest fears at the time was overpopulation — sometimes called Malthusianism after an 18th-century demographer, Thomas Malthus , who proposed that population would eventually grow faster than food production, meaning that, eventually, humanity would be unable to feed everyone. Many early environmentalists proposed similar ideas.

In the 1950s, an animal behaviorist named John Calhoun started working at the National Institute of Mental Health. He had long worked with rats, the subject of his Ph.D. thesis, and was interested in studying how a rat society would develop over time when it was limited only   by space. In other words, he wanted to test the effects of overpopulation.

In order to run his experiment, Calhoun designed complexes, which he named "Universes," that would provide his rodent subjects all they needed to survive — food, water and protection from predators and disease. The only thing that would limit the population growth would be space. 

As he watched the rodent societies grow, he began noticing strange trends:

Pregnant females began having problems raising offspring. Dominant males became incredibly territorial and overactive, while subordinate males increasingly withdrew from the larger group, coming out "to eat, drink and move about only when other members of the community were asleep." Rats became so conditioned to eating with others that they would refuse to eat alone. Some males became hypersexual and attempted to mate with anyone and everyone. Fighting was frequent. Rats began cannibalizing other rats. At one point, the infant mortality rate reached an astonishing 96%.

As one of Calhoun's assistants put it, "utopia" had turned into a "hell."

The Experiments

Calhoun published the results of his early experiments in the February 1962 edition of Scientific American, with the title " Population Density and Social Pathology ," coining the term " behavioral sink " to describe the most-crowded spots, where he observed the highest rate of antisocial behavior. In the 1960s, at the height of political discourse about so-called "social decay" in American cities, the study was a natural discussion topic. In the meantime, Calhoun continued his work.

And now we arrive the 25th version of this study Calhoun ran, and the one he would become most well-known for: Universe 25. It was the only one of Calhoun's habitats fully studied from beginning to end. Universe 25 was populated with mice instead of rats, but most everything else remained the same. Mice had everything they needed to survive and were limited only by space.

Calhoun constructed a square box with a side length of 54 inches. He built nesting boxes, water bottles and food hoppers into the walls, with each side of the universe having 64 different nesting boxes located at various heights, 16 water bottles and four food hoppers. All of the "utilities" were accessible via a series of mesh tunnels running from the floor up the side of the wall.

Calhoun published the results of Universe 25 in 1973 in a paper called " Death Squared: The Explosive Growth and Demise of a Mouse Population ." He broke down the development and collapse of the society into four phases:

• Phase A, consisting of the first 104 days, was the adjustment phase, with "considerable social turmoil" between the eight original mice placed into the habitat. Phase A ended once the mice had their first offspring.
• Phase B, which Calhoun named the resource exploitation phase, lasted from Day 105 to Day 315. During this phase, the population grew rapidly, reaching more than 600 mice before growth began slowing. Social stratification also began to happen, with different groups of mice living in certain areas and self-selecting into their own independent groups.
• Phase C, called the stagnation phase, lasted from Day 316 to Day 560. Male mice who were not able to find room in the pre-existing social structure began to withdraw from society, violently attacking one another. Their female counterparts retreated into the highest boxes, also isolating themselves. Socially dominant males began to lose control over their territory, leaving mothers to aggressively defend their young, sometimes even abandoning them. "For all practical purposes there had been a death of societal organization by the end of Phase C," Calhoun wrote.
• Phase D was the death phase. The death rate outpaced the birth rate, and the society began to shrink. Mothers raised newborn mice for a very short time, and Calhoun proposed that the young generation's strange behaviors were a direct result of a very abnormal social upbringing that did not allow some of the more "complex behaviors," including mating rituals, to develop. Females rarely gave birth, and a large group of males, which Calhoun named the "beautiful ones," did nothing other than eat, drink, sleep and groom themselves. During Phase D, a few mice were placed in newly established universes to see whether they would relearn those social behaviors. They did not.

Calhoun's 1973 paper was not subtle. "I shall largely speak of mice, but my thoughts are on man, on healing, on life and its evolution," he wrote. He made frequent references to the Book of Revelation in the Bible and almost all of his wording aimed to personify his rodent subjects. The mice in Universe 25 lived in "walk-up apartments," and Calhoun described subgroups like "somnambulists" or the "bar flies," terms that could easily be mapped to urban life.

The conclusions felt grim, and the fears of overpopulation made their way into pop culture , like the movie "Soylent Green." There's even a book for children very loosely based around Calhoun's mouse cities (although without the doom and gloom of societal breakdown): "Mrs. Frisby and the Rats of NIMH."

The Conclusions

In modern times, Calhoun's Universe 25 experiment is often used as a way to talk about some kind of " degradation of Western society ." These analyses look at Calhoun's experiments and say, "He predicted this would happen to humans, and look at all the cultural degeneracy we see today!" For instance, here's an excerpt from a comment about the experiment we've seen repeatedly on Facebook :

According to Calhoun, the death phase consisted of two stages: the "first death" and "second death." The former was characterized by the loss of purpose in life beyond mere existence — no desire to mate, raise young or establish a role within society. As time went on, juvenile mortality reached 100% and reproduction reached zero. Among the endangered mice, homosexuality was observed and, at the same time, cannibalism increased, despite the fact that there was plenty of food. Two years after the start of the experiment, the last baby of the colony was born. By 1973, he had killed the last mouse in the Universe 25. John Calhoun repeated the same experiment 25 more times, and each time the result was the same. Calhoun's scientific work has been used as a model for interpreting social collapse, and his research serves as a focal point for the study of urban sociology. We are currently witnessing direct parallels in today's society ... weak, feminized men with little to no skills and no protection instincts, and overly agitated and aggressive females with no maternal instincts.

Scientists have repeatedly pushed back against these ideas since Calhoun's research came out. Researchers who attempted to replicate Calhoun's studies in humans found mixed results, and other scientists chastised him for extrapolating rodent behavior to humans. While the popular conception of Universe 25 focused on the apocalyptic death of society because of overpopulation, other psychologists suggested otherwise. 

In an 2008 interview with the NIH Record , Dr. Edmund Ramsden, a science historian, explained the results of a similar 1975 experiment by a psychologist Jonathan Freedman:

Freedman's work, Ramsden noted, suggested that density was no longer a primary explanatory variable for society's ruin. A distinction was drawn between animals and humans. "Rats may suffer from crowding; human beings can cope… Calhoun's research was seen not only as questionable, but also as dangerous." Freedman suggested a different conclusion, though. Moral decay resulted "not from density, but from excessive social interaction," Ramsden explained. "Not all of Calhoun's rats had gone berserk. Those who managed to control space led relatively normal lives." Striking the right balance between privacy and community, Freedman argued, would reduce social pathology. It was the unwanted unavoidable social interaction that drove even fairly social creatures mad, he believed.

But what the modern critics often carelessly and conveniently leave out is how Calhoun's research evolved after Universe 25: Up until his death in 1995, Calhoun looked for solutions to the problem he had discovered, altering his designs and controls to try to   avoid the societal collapse of Universe 25. He described rodents coming up with creative solutions to daily tasks. And it was in this way that his experiments have actually proven more useful. Architects and urban designers have taken Calhoun's experiments into consideration when designing buildings and cities. Prison researchers and reformers have also found Calhoun's studies surprisingly helpful.

So yes, while Universe 25 and Calhoun's "rodent utopias" were real experiments, they're not the apocalyptic predictions that some people make them out to be. 

Arnason, Gardar. "The Emergence and Development of Animal Research Ethics: A Review with a Focus on Nonhuman Primates."  Science and Engineering Ethics , vol. 26, no. 4, 2020, pp. 2277–93.  PubMed Central , https://doi.org/10.1007/s11948-020-00219-z.

Britannica Money . 18 Mar. 2024, https://www.britannica.com/money/Malthusianism.

Calhoun, John B. "Death Squared: The Explosive Growth and Demise of a Mouse Population."  Proceedings of the Royal Society of Medicine , vol. 66, no. 1P2, Jan. 1973, pp. 80–88.  DOI.org (Crossref) , https://doi.org/10.1177/00359157730661P202.

Calhoun, John B. "Population Density and Social Pathology."  California Medicine , vol. 113, no. 5, Nov. 1970, p. 54.  PubMed Central , https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1501789/.

---. "Space and the Strategy of Life."  Behavior and Environment: The Use of Space by Animals and Men , edited by Aristide Henri Esser, Springer US, 1971, pp. 329–87.  Springer Link , https://doi.org/10.1007/978-1-4684-1893-4_25.

Edmund Ramsden and Jon Adams. "Escaping the Laboratory: The Rodent Experiments of John B. Calhoun & Their Cultural Influence."  Journal of Social History , vol. 42, no. 3, 2009, pp. 761–92.  DOI.org (Crossref) , https://doi.org/10.1353/jsh.0.0156.

Environmentalism | Ideology, History, & Types | Britannica . https://www.britannica.com/topic/environmentalism. Accessed 17 May 2024.

Fredrik Knudsen.  The Mouse Utopia Experiments | Down the Rabbit Hole . 2017.  YouTube , https://www.youtube.com/watch?v=NgGLFozNM2o.

Garnett, Carla. "Medical Historian Examines NIMH Experiments In Crowding."  NIH Record , Vol. LX, No. 15, 25 July 2008, https://nihrecord.nih.gov/sites/recordNIH/files/pdf/2008/NIH-Record-2008-07-25.pdf.

Magazine, Smithsonian, and Maris Fessenden. "How 1960s Mouse Utopias Led to Grim Predictions for Future of Humanity."  Smithsonian Magazine , https://www.smithsonianmag.com/smart-news/how-mouse-utopias-1960s-led-grim-predictions-humans-180954423/. Accessed 17 May 2024.

Magazine, Smithsonian, and Charles C. Mann. "The Book That Incited a Worldwide Fear of Overpopulation."  Smithsonian Magazine , https://www.smithsonianmag.com/innovation/book-incited-worldwide-fear-overpopulation-180967499/. Accessed 17 May 2024.

Paulus, Paul.  Prisons Crowding: A Psychological Perspective . Springer Science & Business Media, 2012.

Ramsden, Edmund. "The Urban Animal: Population Density and Social Pathology in Rodents and Humans."  Bulletin of the World Health Organization , vol. 87, no. 2, Feb. 2009, p. 82.  PubMed Central , https://doi.org/10.2471/BLT.09.062836.

The Calhoun Rodent Experiments: The Real-Life Rats of NIMH . https://cosmosmagazine.com/science/mathematics/calhoun-rodent-experiments/. Accessed 17 May 2024.

"Universe 25, 1968–1973."  The Scientist Magazine® , https://www.the-scientist.com/universe-25-1968-1973-69941. Accessed 17 May 2024.

Woodstream, Woodstream.  What Humans Can Learn from Calhoun's Rodent Utopia . https://www.victorpest.com/articles/what-humans-can-learn-from-calhouns-rodent-utopia. Accessed 17 May 2024.

By Jack Izzo

Jack Izzo is a Chicago-based journalist and two-time "Jeopardy!" alumnus.

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John B. Calhoun papers, 1909-1996 http://oculus.nlm.nih.gov/calhoun586 Archives and Modern Manuscripts Collection, History of Medicine Division, National Library of Medicine, Bethesda, MD; MS C 586.

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Universe 25: the horrifying study that predicted human extinction, one of the longest and most important scientific experiment.

by Andrei Tapalaga | Sep 21, 2022 | Science

The room he planned for his last experiment could have held 3,840 mice, but only 2,200 mice ended up there, and from then on, the population started to fall while showing a range of odd, sometimes destructive behaviours. The outcome demonstrated what Calhoun called the behavioural sink, or an increase in abnormal behaviours brought on by the stress of a large population.

The dominant males occasionally bite and injure the tails of other members, especially young children. This behavioural sink would show up in females as a decreased capacity for raising young and creating nests. Since many females adopted more violent behaviours or would forego motherly responsibilities entirely, the infant death rate exceeded 90%.

Regardless of the scale of the experiments, the same set of events would transpire each time:

With their findings, they concluded the experiment while predicting that these pathological alterations would eventually result in the extinction of the colonies. He would select the four healthiest males and females at the end of the experiment and allow them to reproduce, but their behavior had been irrevocably changed, and none of their offspring had survived.

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How 1960s Mouse Utopias Led to Grim Predictions for Future of Humanity

John Calhoun studied behavior during overcrowding in mice and rats

Maris Fessenden

Former correspondent

What does utopia look like for mice? According to a researcher who did most of his work in the 1950s through1970s, it might include limitless food (of course!), multiple levels and secluded little rodent condos. These were all part of John Calhoun’s experiments to study the effects of population density on behavior. But what looked like rat utopias and mouse paradises at first quickly spiraled into out-of-control overcrowding, eventual population collapse and seemingly sinister behavior patterns.

The mice were not nice.

For io9, Esther Inglis-Arkell writes about Calhoun’s twenty-fifth habitat and the experiment that followed:

At the peak population, most mice spent every living second in the company of hundreds of other mice. They gathered in the main squares, waiting to be fed and occasionally attacking each other. Few females carried pregnancies to term, and the ones that did seemed to simply forget about their babies. They'd move half their litter away from danger and forget the rest. Sometimes they'd drop and abandon a baby while they were carrying it. The few secluded spaces housed a population Calhoun called, "the beautiful ones." Generally guarded by one male, the females—and few males—inside the space didn't breed or fight or do anything but eat and groom and sleep. When the population started declining the beautiful ones were spared from violence and death, but had completely lost touch with social behaviors, including having sex or caring for their young.

Calhoun’s experiments, which started with rats an outdoor pen and moved on to mice at the National Institute of Mental Health during the early 1960s, were interpreted at the time as evidence of what could happen in an overpopulated world. The unusual behaviors he observed he dubbed "behavioral sinks."

After Calhoun wrote about his findings in a 1962 issue of Scientific American , that term caught on in popular culture, according to a paper published in the  Journal of Social History . The work tapped into the era’s feeling of dread that crowded urban areas heralded the risk of moral decay — and events like the murder of Kitty Genovese (though it was misreported) only served to intensify the worry. A host of science fiction works — books like Soylent Green , comics like 2000AD — played on Calhoun’s ideas and those of his contemporaries . The work also inspired the 1971 children’s book Mrs. Frisby and the Rats of NIMH , which was also made into a 1982 film The Secret of NIMH , notes the National Institutes of Health .

Now, interpretations of Calhoun’s work has changed. Inglis-Arkell explains that the habitats he created weren’t really overcrowded, but that isolation enabled aggressive mice to stake out territory and isolate the beautiful ones. She writes, " Instead of a population problem, one could argue that Universe 25 had a fair distribution problem ."

But we can take comfort in the face that humans are not mice. The NIH Record spoke to medical historian Edmund Ramsden about Calhoun’s work:

Ultimately, “[r]ats may suffer from crowding; human beings can cope," Ramdsen says. "Calhoun’s research was seen not only as questionable, but also as dangerous.” Another researcher, Jonathan Freedman, turned to studying actual people — they were just high school and university students, but definitely human. His work suggested a different interpretation. Moral decay could arise “not from density, but from excessive social interaction,” Ramsden says. “Not all of Calhoun’s rats had gone berserk. Those who managed to control space led relatively normal lives.”

Calhoun’s work didn’t give us answers, but it is rare that any single study or series of studies can draw definite conclusions. Instead we have ideas and some strange footage of old experiments about mouse utopias:

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Maris Fessenden | | READ MORE

Maris Fessenden is a freelance science writer and artist who appreciates small things and wide open spaces.

• Experiments

Universe 25: An Experiment With Disturbing Results

The Universe 25 experiment

John Calhoun was an ethologist who worked for much of his life for the US National Institute of Mental Health . In the mid-20th century, overpopulation and overcrowding were of great concern to the scientific community. This researcher had been addressing these issues since the 1950s.

In 1968, Calhoun commenced the experiment known as Universe 25 on a rural property in Poolesville, Maryland. His  objective was to study behavior in the context of the overpopulation of a species. For this purpose, he built a veritable Garden of Eden for the mice, with multiple nesting areas and constant sources of food and water.

It was a kind of metallic corral with tunnels. It measured 2.7 meters wide by 1.4 meters high. The mice had everything they needed, except space. Now, let’s find out the results.

You might also like to read Telepathy Experiments in Silicon Valley

From the Garden of Eden to extinction

In 1968, four pairs of mice were introduced into the habitat. Over time, every 55 days, the number of births doubled. By month 19 of the experiment, there were 2,200 mice. This reproductive rhythm was explained by the absence of predators and permanent access to food.

It appeared to be an ideal society. However, certain phenomena of great interest to the field of social psychology occurred. They were as follows:

• Hierarchies were established. Dominant alpha males controlled female harems.
• Mice that lost fights with the dominant males created groups of ‘breakaways’.
• Fights were constant. That was until the alpha males stopped defending their groups of females.
• The females had to initiate defense behaviors for their young. But, the levels of violence were so high that they ended up abandoning or neglecting their offspring.
• Between days 315 and 600, aberrant behaviors occurred that broke the social structure.
• The females became aggressive and many stopped getting pregnant.
• Compulsive sexual behavior occurred. This included mating between mice of the same sex.
• There were incidences of cannibalism.
• The mice stopped creating social ties.
• From day 600, they stopped reproducing and defending their territories. In fact, they limited themselves to carrying out basic tasks for their health, like feeding and grooming.
• The population, faced with the total breakdown of all social patterns, gradually became extinct.

In 1973, less than five years after the start of the experiment, the population went from 2,200 mice to none.

The young that were born into the chaotic environment dominated by violence received no protection. Nor did they establish bonds between them. This ultimately led to total extinction.

The conclusions of the experiment

Dr. Calhoun didn’t hesitate to anthropomorphize the behavior of the mice. For example, throughout the experiment, he classified them as juvenile delinquents and social deserters. Later, his terminology was criticized. Calhoun’s study was published in the journal, The Royal Society of Medicine. He came to the following conclusions:

1. The behavioral sink

Calhoun coined a new term. He called the set of aberrant behaviors that appear in crowded conditions and break the social order a behavioral sink . Moreover, he stated that when the number of individuals occupying a space exceeds balance and harmony, three types of responses appear:

• Compulsive and irrational violence.
• Neglect of the most basic bonds. For instance, caring for offspring.
• Withdrawal and isolation of some individuals to focus only on their personal hygiene and subsistence tasks (food). Calhoun called these the ‘beautiful ones’.

2. Some innovative behaviors

The famous experiment also yielded some hopeful data. This was the fact that some mice demonstrated innovative behavior. Indeed, a few of them, faced with a chaotic, threatening, and declining context, created tunnels in order to escape from the hostile environment. Others built higher cubicles so that they wouldn’t have to come into contact with the most crowded and violent areas.

3. Individuals without status

When the mice stopped fighting over their territories, they lost status. The same thing happened with the females once they realized that they couldn’t take care of their young. The environment was so hostile that the social hierarchy fell apart . Moreover, certain social behaviors arose as a reflection of helplessness and abandonment.

When individuals don’t exhibit mature social behaviors, the development of an organization or social community doesn’t occur.

4. A (questionable) analogy of today’s world

John Calhoun presented his work on mouse behavior as an analogy for the world of the time. This was in the 70s and population growth was high. Dr. Edmund Ramsden, from Queen Mary University of London (UK), published an interesting essay regarding the experiment in 2011. He claimed that:

• Calhoun’s studies were presented to reflect on or justify the need for population control, especially in the most disadvantaged communities.
• The experiment should be interpreted with caution. In fact, he started a debate, essentially academic, regarding whether this type of study could be extrapolated to human societies.

You might be interested in The Tuskegee Experiment and the Foundation of Bioethics

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

• Calhoun, J.B. (1971). Space and the Strategy of Life. In: Esser, A.H. (eds) Behavior and Environment. Springer, Boston, MA. https://doi.org/10.1007/978-1-4684-1893-4_25
• Calhoun JB. (1973). Death Squared: The Explosive Growth and Demise of a Mouse Population. Proceedings of the Royal Society of Medicine , 66 (1P2),80-88. doi:10.1177/00359157730661P202
• Freedman, J. L. (1975). Crowding and behavior. W. H. Freedman. https://psycnet.apa.org/record/1976-05842-000
• Ramsden E. (2011). From rodent utopia to urban hell: population, pathology, and the crowded rats of NIMH.  Isis; an international review devoted to the history of science and its cultural influences ,  102 (4), 659–688. https://doi.org/10.1086/663598

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.

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The Universe 25 Mouse Experiments

In 1972, John B. Calhoun built an utopia for mice. Every aspect of Universe 25 , as this particular model was called, was designed to cater for the well-being of its rodent residents, increase their lifespan, and allow them to mate. It was not the first time the ethologist had built a world for rodents. Colhoun had been creating utopian environments for rats and mice since the 1940s, with consistent results: overpopulation leads to explosive violence and hypersexual activity, followed by asexuality, self-destruction, and extinction.

The full story

Cannibalism, asexuality, and violence. A society that had collapsed.  What’s going on here? In 1972, John B Calhoun detailed the specifications of an utopia designed for mice: built in the laboratory.

universe 25

Every aspect of Universe 25 , as this particular model was called, was designed to cater for the well-being of its rodent residents, increase their lifespan, and allow them to mate. There was abundant food, water, and nesting material. The universe was cleaned regularly. There were no predators, the temperature stable. Paradise. Or maybe not?

Beginning of experiment

Four pairs of disease-free mice, selected from the National Institutes of Health’s elite breeding colony, moved in on day one .

It took months for the rodents to familiarize themselves with their new world. Then they started to reproduce and the population increased exponentially, doubling every fifty-five days. Those were the good times in paradise.

Population growth

Past day 315, more than six hundred mice now lived in Universe 25, rubbing shoulders on their way up and down the stairwells to eat, drink, and sleep. Population growth slowed.

Young ones found themselves born into a world with far more mice than meaningful social roles. Males faced a lot of competitors to defend their territory against. Many found that so stressful, they gave up. Normal discourse within the community broke down, and with it the ability of mice to form social bonds.

Lone females retreated to isolated nesting boxes on penthouse levels.  Other males, a group Calhoun termed “the beautiful ones,” never sought sex and never fought — they just ate, slept, and groomed, wrapped in narcissistic introspection. Elsewhere, cannibalism, asexuality, and violence became endemic. Mouse society had collapsed.

population peaks

On day 560 the population peaked at 2,200 mice. A few survived past weaning until day six hundred, after which there were few pregnancies and no surviving young. As the population had stopped regenerating itself, its path to extinction was clear.

The mice had lost the capacity to rebuild their numbers—many that could still conceive, such as the “beautiful ones” and their secluded singleton female counterparts, had lost the social ability to do so.

the last conception

On day 920 was the last conception. The last mouse died on May 23 1973, four years and ten months after colonization. Calhoun later said that the creatures had died two deaths. The first was that of their spirit and their society. The “second death” was that of their physical body.

It was not the first time the ethologist had built a world for rodents. Colhoun had been creating utopian environments for rats and mice since the 1940s, with consistent results: overpopulation leads to explosive violence and hypersexual activity, followed by asexuality, self-destruction, and extinction.

In his widely cited paper, “Population Density and Social Pathology”, Calhoun concluded: No matter how sophisticated we are, once the number of individuals capable of filling social roles greatly exceeds the number of such roles, only violence and disruption can follow.

He then referred to a phenomenon he called “Behavioral Sink”

Behavioral sink

Behavioral sink is our desire to be in the presence of others, to be conditioned to seek to be near others, and to be drawn to the crowd, in spite of the conflicts that this can generate. 

Drawing from Calhoun’s popular research, social scientists started to call for restrictions on reproduction as the only possible response to the world’s rising population. Calhoun himself was more optimistic about our future. He argued: as our physical space declines, we are forced to extend a conceptual space — our network of ideas and technologies.

Later in his career he turned to possible solutions and began to build creative universes that minimize the ill effects of overcrowding. 

what do you think?

What are your thoughts? Is overcrowding a danger for mankind or does it only affect rodents? And if so, what can save the human psyche? Avoiding eye contact in crowded places is one strategy, but is that enough? To read more about Universe 25, and its cultural impact, read the paper of Edmund Ramsden & Jon Adams. You’ll find a link in the description below.

• Life of John.B. Calhoun – Wikipedia.org
• Edmund Ramsden & Jon Adams, “ Escaping the Laboratory: The Rodent Experiments of John B. Calhoun & Their Cultural Influence ,” The Journal of Social History, vol. 42, no. 3 (2009).
• Wiles, W. (2011). The Behavioral Sink : The mouse universe of John B. Calhoun .  Cabinet , (42).
• John B. Calhoun, “ Death Squared: The Explosive Growth and Demise of a Mouse Population, ” in Proceedings of the Royal Society of Medicine, vol. 66 (January 1973), pp. 80-88.
• John B. Calhoun, “ Population Density and Social Pathology, ” Scientific American, vol. 206, no. 2 (February 1962), pp. 139–150.

Dig deeper!

• Watch Soylent Green, 1973. The film depicts a futuristic society in which overpopulation is so catastrophic and food in such short supply that the populace survives on rations of the titular food product, which turns out to be made from processed human flesh.
• Watch “In Time”, a Film of 2011 where Time is money, and people out of money die. 
• Watch Snowpiercer (Netflix, 2020) depicting a society in a train where population has to be controlled and the ecosystem rests on a very thin equilibrium. 
• Read about Behavioral Sink on Longreads
• Read about the life and work of John B Calhoun

Classroom activity

In the following activity students will learn about Calhoun’s work and Universe 25

• Separate the class in groups of 3 or 4.
• Ask the students how they think society would evolve if everyone had access to food, water, shelter, and ideal conditions of life, and ask them to describe how society would be in 25 years if all of this became immediately available. 
• Show the students Sprouts video on Universe 25.
• Ask them if they think the downfall of mice was led by overpopulation and its results or by a lack of survival drive due to the abundance of resources.
• Ask them if they want to change their answer from the first question.
• Ask them if they think there are fundamental differences between humans and mice that would justify a different answer for the first question.

Collaborators

• Script: Edmund Ramsden & Jon Adams
• Editor: Will Wiles, a London-based author and journalist
• Screenplay: Jonas Koblin 
• Artist: Pascal Gaggelli
• Voice: Matt Abbott
• Coloring: Nalin
• Editing: Peera Lertsukittipongsa
• Sound Design: Miguel Ojeda
• Fact Checking: Ludovico Saint Amour di Chanaz
• Production: Selina Bador

One Reply to “The Universe 25 Mouse Experiments”

This is a very important article — thanks for writing it.

I personally think that, in the human species, the real issue is not sheer numbers of people in existence, but the sheer number of genetic sociopaths present, as these are the people who tend to selectively breed more and more free-roaming sociopaths who disproportionately make life hell for all the rest of us who are more innately inclined to park within the lines and not just drop our trash just anywhere — including within single-digit feet of an obviously present and empty trash can.

Also, you mention the movie “Soylent Green”. But do you know what year that movie is set in? Check out images of the movie marquee poster — the year “Soylent Green” is set in, is the year 2022. When I tell people that, they are unnerved.

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Universe 25 Project: The failed mice utopia

In 1968, John B. Calhoun, an American ethologist, and behavioral researcher, created the Universe 25 Project. For this study, he built a mice utopia purposefully designed to provide the mice with everything they needed and satisfy their every whim.

In essence, he created a perfect society of mice to study their behavior and see if they would thrive. Spoiler alert: they didn’t. But why? And what does that mean for humans? Well, that is exactly the point of this article today.

Calhoun’s Early Experiments

Calhoun dedicated his entire career to the study of population density and its effects on behavior. He was focused on the problem of crowding, which led him to conduct a series of experiments and studies using rats and mice as subjects.

His experimental research started in 1947. That year, he started a 28-month study of a colony of Norway rats at Johns Hopkins University. The colony of Norway rats was enclosed in a 10,000 square-foot outdoor pen, where they were supplied with unlimited water and food.

The rat population was expected to reach 5,000 over the course of the experiment; however, the population never grew beyond 200 and it stabilized at 150. During the study, the rats subdivided themselves into small groups of up to 12 individuals.

Calhoun noted that 12 was the maximum number of rats that could live in harmony; anything beyond that would lead to stress and psychological effects causing the group to break.  

This confirmed Calhoun’s central contention that there is a limit to the number of meaningful interactions individuals can cope with before stress enters the picture. So, as the rat population increased, it became difficult for individuals to control how often they had social contact.

That lead to unwanted interaction, which made them hostile and withdrawn. Ultimately, this caused a psychological breakdown and the rat society would collapse and they would become extinct.

He continued studying rats throughout the 1950s, building more complex enclosures for the rats to examine how they would behave in an environment where they never lacked food and water, and that was predator-free. All the experiments would lead to the same sequence of events:

• At first, the mice would meet, mate, and breed abundantly.
• Then, the society would reach a leveling-off point.
• After that, the mice would either become hostile or form cliques or passive and anti-social.
• Eventually, they would become extinct.

The Introduction of Behavioral Sink

In 1962, Calhoun wrote about his research in an article for the Scientific American called “Population Density and Social Pathology.” In this article, he coined the term “behavior sink” to describe the breakdown of social functions and population collapse that stemmed from overcrowding in his rodent enclosures.

Calhoun described this behavioral sink as a kind of para-pathology that appears from, and succeeds upon, the behavior of individual animals within a group. In other words, the behavioral sink would emerge from erratic behavior and then act as an accelerant of other pathological behaviors. Essentially, it would exacerbate all kinds of pathology present in a group, thus making crowding lethal.

This publication was met by a receptive audience and the period that followed would see a surge of movies, books, and even comics that would depict an apocalyptic view of the future as a result of over-population, undoubtedly influenced by Calhoun’s findings.

It is important to note that behavioral sink could be avoided by altering feeding arrangements to reduce social contact. When the behavioral sink was prevented, Calhoun found that crowding became less lethal, but it was still not ideal by any means. 

The Universe 25 Project

Expanding on earlier studies, Calhoun created his ultimate research experiment, dubbed Universe 25. For this one, he used mice and he built a tank that was 101 inches square, enclosed by walls that were 54-inch high. Every wall featured 16 vertical mesh tunnels which can be called stairwells.

Four horizontal corridors opened from each stairwell, leading to 4 rooms. In total, there were 256 rooms, or “nesting boxes” as Calhoun called them, that could house 15 mice each. There were also 16 burrows leading to unlimited food and water.

According to Calhoun’s calculations, the enclosure could reliably and comfortably house up to 3,840 mice. The environment was plague-free, predator-free, and specifically designed so the mice would not lack anything at all.

For the experiment, Calhoun decided on 4 breeding pairs of mice that were specifically bred for Universe 25. These specimens were hand-picked to make sure they were the healthiest ones and they were provided by the National Institute of Health.

The Course of the Experiment

The specimens were released into the enclosure so they could start their society and the evolution of this mice utopia was categorized in a series of phases. Phase A marked the initial period of adjustment, Phase B marked the beginning of population growth, Phase C marked the final period of population growth, and Phase D marked the decline and extinction of the population.

During Phase A and B, the experiment seemed quite promising. Phase C took a sour turn, though. At this point, the population increased tremendously, which reduced the availability of meaningful societal roles. Helpless males became inactive and separated themselves from the rest in large pools located near the center of the universe’s floor. They no longer interacted with others.

Though territorial males didn’t attack these social rejects, so to speak, violence was still prominent, leading the dominant males to lose their ability to defend the females. This led to nest invasions and infant mortality.

Mice born during Phase C didn’t experience normal social interactions, so they didn’t develop the skills to court, care for infants, or defend their territory. You can imagine how detrimental that was to their development.

By the time Phase D rolled around, there were no young and the mice who survived couldn’t conceive or simply didn’t want to. Eventually, that led to their extinction.

A More in-Depth Look Into Universe 25

• Phase A and B

Phase A, called the “strive period”, lasted 104 days. During this time, the mice adjusted to their new environment, marked their territory and started to nest. Then came Phase B, called the “exploit period”, where the population doubled every 55 days. On day 315, the population on Universe 25 rose to 620 mice. Though space was abundant, mice crowded in select areas and they feed on the same food sources. This made eating a communal activity.

However, since they were always huddling together, they stopped mating as much and the birthrate started to fall. This created an imbalance where one-third of the mice became socially dominant and the other two-thirds became less socially adept. Bonding skills started to decline, which marked the beginning of the end for Universe 25.

The high and low status of the mice became more pronounced and those at the bottom were rejected by females, so they stopped mating. They became outcasts because they didn’t have a role in society, so they wandered off and started sleeping and eating alone. Occasionally, they would fight among them.

By contrast, the males at the top became more aggressive and turned to aimless violence. Sometimes they would even roam around and violate other mice no matter their gender. These were the alpha males. The beta males, the mice between the alpha and the outcast, became timid and passive receptors of violence, which ended very badly.

Males completely abandoned their traditional roles in society, so the females had to defend their nests on their own. Consequently, many of them became aggressive and would turn violent towards their babies, while others would abandon their babies altogether and withdraw from mating. As you can imagine, infant mortality skyrocketed, reaching 90%.

Calhoun called Phase C the “stagnation phase” and attributed the overly aggressive and passive behavior to the breakdown of social roles and the increasing over-clustering. By day 560, the population ceased to increase and the mortality rate was almost at 100%.

Finally, we enter Phase D, the “death phase”. Among all this violence and lack of mating, a younger generation of mice became adults. However, they were never exposed to what we would call a normal society. As a result, they had no social skills and they never experienced normal or healthy relations.

They had no concept of marking territory, mating, or parenting, so all they did was eat, sleep and groom themselves. Calhoun called them the “beautiful ones” and they chose to be secluded, so they didn’t experience any violence or conflict but they also made no contributions to their society.

Calhoun noted that the death phase happened in two stages; the first death, which is the death of the spirit, meaning that mice had no purpose beyond existing and had no desire to mate, raise, or have a role in society, and the second death, which is the literal end of life.

In time, the number of mice that no longer wanted to mate or be a part of society grew more and more until they outnumbered the gangs. Universe 25 came to an end on day 920, where the population capped at 2,200. There was still an endless supply of food, water, and resources, but behavior sink had already taken hold and demise was inevitable. Soon enough, all the mice were dead.

What Does This Mean?

Calhoun, based on his observations of the beautiful ones in Universe 25, came to the conclusion that mice, just like humans, thrive when they have a sense of purpose and identity in the world they live in and find themselves. Experiencing stress, tension, anxiety, and the need for survival is what leads to engaging in society.

As the experiment showed, when all needs are accounted for and there are no conflict whatsoever, living is reduced to eating and sleeping, because that is all they have to do to survive. In other words, when necessity is taken away, life no longer has purpose and the spirit dies.

From the rise and fall of the mice utopia, Calhoun was able to draw these five basic points about mice and humans:

• Mice are simple creatures, but they need the skills for courtship, child-rearing, territorial defense, and a role to fulfill in the domestic and communal front. If they fail to develop those skills, they won’t reproduce nor find a productive role in society.
• Mice, like all other species, grow old and die. Nothing suggests that human society is not prone to the same developments that brought Universe 25 crashing down.
• If the number of unqualified individuals outgrows the number of openings in society, chaos and alienation are inevitable.
• Individuals raised in these conditions won’t be able to relate to the world and physiological fulfillment (eating and sleeping) will become their only drive.
• Just as mice thrive on complex behaviors, the concern for other people stemming from human skills and understanding is vital for our species to survive. If these attributes are lost, civilization as we know it would collapse.

Calhoun concluded that when complex behaviors related to vital functions (courtship, maternal care, etc.) don’t mature, social organization and reproduction just stop. So, the population will age and die, leading to extinction.

At the time, his conclusions resonated with the way people felt about overcrowding in urban areas and how it led to “moral decay”, but that leaves out many factors that contribute to that beyond overcrowding, such as prejudice and poverty.

Despite the grim picture Calhoun’s conclusions painted, he wasn’t implying that humankind would take a similar path. He described the parallels between his experiment and certain issues in society, but he also emphasized that humans are a more evolved species with the wisdom to avoid the trends he found.

After all, we have technology, science, and medicine, which give us many amazing skills, such as the ability to explore new environments, determine causation, avoid disasters, heal illnesses, injuries, and wounds, etc. Also, Universe 25 was not a natural environment, it was entirely manufactured and purposefully designed.

However, he did fear humanity could go down that dark path if the population grew beyond the job market’s capacity and cities became overcrowded. That’s why he dedicated his later career to exploring human advancement, which led him to the concept of space colonization, as well as city planning.

At the end of the day, humans are a more sophisticated species and the access we have to science, medicine, and technology can help us prevent such a fate. Not to mention, we have a wide variety of outlets that allow us to find meaning and purpose in life beyond eating and sleeping.

Featured photo is by Pixabay from Pexels

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IsItBullshit: I've read this article on 'Universe 25' mouse experiment. Please tell me if some part of the article or the whole original research is bullshit.

The "Universe 25" experiment is one of the most terrifying experiments in the history of science, which, through the behavior of a colony of mice, is an attempt by scientists to explain human societies. The idea of ​​"Universe 25" Came from the American scientist John Calhoun, who created an "ideal world" in which hundreds of mice would live and reproduce. More specifically, Calhoun built the so-called "Paradise of Mice", a specially designed space where rodents had Abundance of food and water, as well as a large living space. In the beginning, he placed four pairs of mice that in a short time began to reproduce, resulting in their population growing rapidly. However, after 315 days their reproduction began to decrease significantly. When the number of rodents reached 600, a hierarchy was formed between them and then the so-called "wretches" appeared. The larger rodents began to attack the group, with the result that many males begin to "collapse" psychologically. As a result, the females did not protect themselves and in turn became aggressive towards their young. As time went on, the females showed more and more aggressive behavior, isolation elements and lack of reproductive mood. There was a low birth rate and, at the same time, an increase in mortality in younger rodents. Then, a new class of male rodents appeared, the so-called "beautiful mice". They refused to mate with the females or to "fight" for their space. All they cared about was food and sleep. At one point, "beautiful males" and "isolated females" made up the majority of the population. As time went on, juvenile mortality reached 100% and reproduction reached zero. Among the endangered mice, homosexuality was observed and, at the same time, cannibalism increased, despite the fact that there was plenty of food. Two years after the start of the experiment, the last baby of the colony was born. By 1973, he had killed the last mouse in the Universe 25. John Calhoun repeated the same experiment 25 more times, and each time the result was the same. Calhoun's scientific work has been used as a model for interpreting social collapse, and his research serves as a focal point for the study of urban sociology.

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New Google AI experiment could let you chat with celebrities, YouTube influencers

Published on June 25, 2024

• According to a new report, Google is working on an AI experiment that could let you chat with famous personalities.
• The project will also allow anyone to build their own chatbots, similar to services like Character.ai.
• The search giant may partner with YouTube influencers to create brand-specific AI personas.

Google is reportedly working on a new AI project that will let you converse with chatbots modeled after celebrities, YouTube influencers, or even fictional characters. According to The Information , Google plans to let anyone create their own chatbot by “describing its personality and appearance” and then converse with it — purely for entertainment.

This latest AI effort is notably distinct from Gems, which are essentially “customized versions of Gemini”. Put simply, Gems are similar to custom GPTs  that can be taught to handle singular tasks like acting as a running coach or coding partner. On the other hand, Google’s upcoming chatbot project will fine-tune the Gemini family of language models to mimic or emulate the response style of specific people.

The search giant’s interest in personalized chatbots might suggest that it’s looking to take on Meta’s Celebrity AI chatbots. The latter already lets you talk to AI recreations of famous personalities like Snoop Dogg. Google’s upcoming product has also drawn comparisons to Character.ai , a chatbot service that offers a diverse range of personas ranging from TV characters to real-life politicians. Character.ai allows you to create your own personas with unique response styles that can be trained via text datasets.

Google’s customizable chatbot endeavor comes courtesy of the Labs team, which pivoted to working on various AI experiments last year. It’s being developed by a team of ten employees and led by long-time Google Doodle designer Ryan Germick.

As for monetization, the report suggests that Google may eventually integrate the project into YouTube rather than launching it as a standalone product. This would allow creators to create their own AI personas and potentially improve engagement with their audiences. YouTube’s most famous personality, MrBeast, already embodies an AI-powered chatbot on Meta’s platforms. While this approach may still not translate to a direct revenue stream, it could convince users to return to YouTube more often and offer creators better reach.

While a release date has yet to be finalized, the chatbot platform will likely make its way to the Google Labs page for testing first. The company is currently showing off over a dozen experimental tools and projects, with some like the controversial AI Overviews already integrated within mainline Google products.

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• Revived Technology Used to Count Individual Photons from Distant Galaxies
• Cosmic Frontiers

Adapted from a release by Fermi National Accelerator Laboratory.

Using an instrument on the 4.1-meter Southern Astrophysical Research (SOAR) Telescope, researchers obtained the first astronomical spectrum using skipper charge-coupled devices (CCDs). Skipper CCDs can get down to very low noise levels, which helps astronomers see distant galaxies.

“We had previously developed skipper CCDs for dark matter detection, and this is the first successful transition of that technology to image faint astronomical objects,” said Steve Holland, a senior engineer in the Physics Division at the Department of Energy’s Lawrence Berkeley National Laboratory. The four science-grade skipper CCDs deployed at SOAR were designed and processed at Berkeley Lab, leveraging the lab’s extensive expertise in CCD technology. This includes the development of “red-sensitive CCDs” for the Dark Energy Camera, Dark Energy Spectroscopic Instrument, and skipper-CCD designs used in dark matter experiments.

On March 31 and April 9, researchers used skipper CCDs to collect astronomical spectra from a galaxy cluster, two distant quasars, a galaxy with bright emission lines, and a star that is potentially associated with a dark-matter-dominated ultra-faint galaxy. In a first for astrophysical CCD observations, they achieved sub-electron readout noise and counted individual photons at optical wavelengths. The results were presented on June 17 at the Society of Photo-Optical Instrumentation Engineers (SPIE) Astronomical Telescopes + Instrumentation meeting in Japan.

“This is a major milestone for skipper-CCD technology,” said Alex Drlica-Wagner, a cosmologist at the DOE’s Fermi National Accelerator Laboratory and associate professor at University of Chicago who led the project. “It helps to retire the perceived risks for using this technology in the future, which is vitally important for future DOE cosmology projects.”

This is an important achievement for a project conceived and initiated through the Laboratory Directed Research and Development program at Fermilab in collaboration with NFS’s NOIRLab detector group. LDRD is a national program sponsored by the DOE that allows national laboratories to internally fund research and development projects that explore new ideas or concepts.

CCDs were invented in the United States in 1969, and forty years later scientists were awarded the Nobel Prize in Physics for their achievement. The devices are two-dimensional arrays of light-sensitive pixels that convert incoming photons into electrons. Conventional CCDs are the image sensors first used in digital cameras, and they remain the standard for many scientific imaging applications, such as astronomy, though their precision is limited by electronic noise.

Cosmologists seek to understand the mysterious natures of dark matter and dark energy by studying the distributions of stars and galaxies. To do this, they need advanced technology that can see fainter, more distant astronomical objects with as little noise as possible.

Existing CCD technology can make these measurements but take a long time or are less efficient. So, astrophysicists must either increase the signal – i.e., by investing more time on the world’s largest telescopes – or decrease the electronic noise.

Berkeley Lab’s Steve Holland designed the skipper CCDs used at SOAR for astronomical observations. After the CCDs were fabricated at Teledyne DALSA in Canada, they were processed at Berkeley Lab’s Microsystems Laboratory. The CCDs were “back illuminated,” which makes them highly sensitive to light. (Credit: Steve Holland/Berkeley Lab)

Skipper CCDs were introduced in 1990 to reduce electronic noise to levels that allow the measurement of individual photons. They do this by taking multiple measurements of interesting pixels and skipping the rest. This strategy enables skipper CCDs to increase the precision of measurements in interesting regions of the image while reducing total readout time.

In 2017, scientists pioneered the use of skipper CCDs for dark matter experiments such as SENSEI and OSCURA , but today’s presentation showed the first time the technology was used to observe the night sky and collect astronomical data.

“What’s incredible is that these photons traveled to our detectors from objects billions of light-years away, and we could measure each one individually,” said Edgar Marrufo Villalpando, a physics PhD candidate at the University of Chicago and a Fermilab DOE Graduate Instrumentation Research Award Fellow who presented the results.

Researchers are analyzing data from these first observations, which used the SOAR Integral Field Unit Spectrograph (SIFS), an instrument built by the National Astrophysical Laboratory. The next scheduled run for the skipper-CCD instrument on the SOAR Telescope is in July 2024.

“Many decades have passed since the skipper was born, so I was surprised to see the technology come to life again many decades later,” said Jim Janesick, inventor of the skipper CCD and a distinguished engineer at SRI International, a research institute based in California. “The noise results are amazing! I fell off my seat when I saw the very clean sub-electron noise data.”

With the first successful demonstration of skipper-CCD technology for astrophysics, scientists are already working to improve it. The next generation of skipper CCDs, developed by Berkeley Lab and Fermilab, is 16 times faster than current devices. Prototypes of the faster CCDs called “Multiple-Amplifier Sensing (MAS)” CCDs have been successfully tested as part of an LDRD led by Julien Guy, a physicist at Berkeley Lab.

“Jim Janesick was extremely helpful during the early days of our CCD development at Berkeley Lab, and it’s exciting to see Jim’s skipper-CCD invention ‘revived’ and merged with the fully depleted, red-sensitive CCDs,” said Holland. Berkeley Lab’s CCD effort formally began with an LDRD in 1995 and was led by Saul Perlmutter, who would later win the Nobel Prize in Physics.

The next generation of skipper CCDs has been identified for use in future DOE cosmology efforts, such as the spectroscopic experiments DESI-II and Spec-S5 recommended by the recent U.S. particle physics planning process . In addition, NASA is considering skipper CCDs for the forthcoming Habitable Worlds Observatory that will attempt to detect Earth-like planets around Sun-like stars.

“I’m looking forward to seeing where these detectors might end up,” said Marrufo Villalpando, who joined the program in 2019. “People are using them for amazing things all over; their utility ranges from particle physics to cosmology. It’s a very versatile and useful technology.”

The project was a close collaboration between physicists, astronomers, and engineers at Berkeley Lab, Fermilab, UChicago, the National Science Foundation’s NOIRLab, and the National Astrophysical Laboratory of Brazil.

Lawrence Berkeley National Laboratory (Berkeley Lab) is committed to delivering solutions for humankind through research in clean energy, a healthy planet, and discovery science. Founded in 1931 on the belief that the biggest problems are best addressed by teams, Berkeley Lab and its scientists have been recognized with 16 Nobel Prizes. Researchers from around the world rely on the lab’s world-class scientific facilities for their own pioneering research. Berkeley Lab is a multiprogram national laboratory managed by the University of California for the U.S. Department of Energy’s Office of Science.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science .