Standing before the Royal Society of Medicine in London on 22 June 1972, the ecologist turned psychologist John Bumpass Calhoun, the director of the Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health (NIMH) headquartered in Bethesda, Maryland, appeared a mild-mannered, smallish man, sporting a greying goatee. After what must surely have been one of the oddest opening remarks to the Royal Society in its storied 200-plus-year history – “I shall largely speak of mice,” Calhoun began, “but my thoughts are on man, on healing, on life and its evolution” – he spoke of a long-term experiment he was running on the effects of overcrowding and population crashes in mice.
Members of the Royal Society were scratching their heads as Calhoun told them of Universe 25, a giant experimental setup he had built and which he described as “a utopian environment constructed for mice”. Still, they listened carefully as he described that universe. They learned that to study the effects of overpopulation, Calhoun, in addition to being a scientist, needed to be a rodent city planner. For Universe 25, he had built a large, very intricate apartment block for mice. There were 16 identical apartment buildings arranged in a square with four buildings on each side. Calhoun told his audience each building had “four four-unit walk-up one-room apartments”, for a total of 256 units, each of which could comfortably accommodate about 15 mouse residents. There were also a series of dining halls in each apartment building, and a cluster of rooftop fountains so the residents could quench their thirst. Calhoun had marked each mouse resident with a unique colour combination and he or his team sat in a loft over this mouseopolis, for hours every day, for more than three years, and watched what unfolded.
Calhoun told the Royal Society members that what began as a rodent utopia – where mice had sumptuous accommodations, all the food and water they could want, and were free from the twin scourges of disease and predation – over time degenerated into a mouse hell. Initiated by a population explosion early on, and later stagnation and decline, that hell had mice displaying a suite of aberrant behaviours, including the loss of sexual drive on the part of males and the absence of maternal care in females. Calhoun attributed much of this to the formation of what he called a behavioural sink that had developed among the mice in Universe 25. At the most general level, a “behavioural sink”, Calhoun argued, was an “attraction to one locality to assure a conditioned social contact”. That attraction could lead to a “pathological togetherness” in which animals needed to be near others, even if the consequences of such togetherness – eating at crowded feeders when more food could be obtained elsewhere – were negative. Once a behavioural sink was in place, “normal social organisation … ‘The establishment,’” he told the crowd, “breaks down, it ‘dies.’”
Even if mice were taken from Universe 25 and placed into another mouse apartment block with a much lower density of residents, Calhoun explained, they still showed these aberrant behaviours. As he summarised his results, Calhoun again befuddled his audience, telling them of a class of mice that had appeared after the rodent population bomb had exploded and the population had rocketed. These were what Calhoun dubbed “the Beautiful Ones” – mice that spent their time grooming themselves and eating and shunned all social behaviour. The Beautiful Ones, Calhoun told his audience, were “capable only of the most simple behaviours compatible with physiological survival”. In time, Calhoun came to believe that if we didn’t act to stop a potential human population bomb from igniting, we would see human parallels.
Calhoun’s work a decade earlier, that time on rats in a barn he had turned into a laboratory, had already been the subject of much attention, garnering stories in newspapers around the world – but now, in conjunction with the mice in Universe 25, his studies of crowding, population growth and the perils of overpopulation in rodents took him to international attention.
No one in attendance at Calhoun’s lecture at the Royal Society of Medicine would soon forget what they heard. Some of the society members knew of Calhoun’s article in Scientific American a decade earlier. That article, on crowding and population crashes in rats, opened with allusions to the 18th-century political economist Thomas Malthus and his ideas on overpopulation and misery. Calhoun then followed with a description of his own results in rats, which centred on the effects of overcrowding and unconstrained population growth. But the Universe 25 mouse experiment results were different. And not just because of the Beautiful Ones, or because these results confirmed what Calhoun found in the rats a decade earlier, but because the work was so much grander, with thousands of mice and many years of data on a topic – population growth and decay – that was of great concern, and not just to scientists. A large swath of the public at the time was terrified of the implications of human population growth as well – largely because of Paul R Ehrlich’s 1968 book The Population Bomb, which shot to the bestseller list after Ehrlich appeared on The Tonight Show with Johnny Carson.
Calhoun’s work was covered in the New York Times, the Washington Post, Time magazine, Der Spiegel and more: “It was a lovely day,” read the opening sentence of a 1970 Newsweek story, “much too lovely to spend in an office. In fact, it seemed the perfect day to visit Dr John Calhoun’s mousery.” In Time magazine’s 1971 article, Population Explosion: Is Man Really Doomed? the writer notes grimly that “even if some way can be found to feed the onrushing millions [of humans], they may still face a psychic fate similar to the one that befell Dr John Calhoun’s white mice”. In April of that year, the US Senate discussed Calhoun’s works on overpopulation in rodents and the implications for our own species, and it enshrined three of his papers in the congressional record.
Many saw Calhoun’s work on overcrowding and population dynamics as a portent of doomsday, but he thought otherwise. Calhoun came to see the results of his work with rodents as prescriptive, showing a path forward to prevent the human population bomb from exploding. Many agreed, but he had his critics, then and now. He dubbed himself a “℞evolutionist” – a revolutionary evolutionist with a prescription (℞) to help fight the problems of overpopulation. He called his ideas “metascientific,” which, for Calhoun, meant using science to try to understand very complex problems involving not just many unknowns but complex interactions between variables. To drive home that complexity, he proposed experiments in rats that would tinker with rodent culture and cooperation, and in so doing, defuse a potential ticking population bomb. “Of course, we realise that rats are not men,” Calhoun once said, “but they do have remarkable similarities in physiology and social relations. We can at least hope to develop ideas that will provide a spring forward for attaining insights into human social relations and the consequent state of mental health.”
Every edition of Forty Studies That Changed Psychology, from the first in 1992 to the latest in 2020, has a chapter that reprints Calhoun’s 1962 Scientific American paper. But, in many ways, the most profound impact of Calhoun’s studies lies far from academic halls and ivory towers. Through the seemingly endless coverage in newspapers and magazines, Calhoun’s work seeped into the public consciousness. City planners and architects in the 1970s and 1980s looked to Calhoun’s results when designing housing developments, and he encouraged them to do so. Each year, Ian McHarg, who years later was awarded the National Medal of Arts and the Thomas Jefferson Foundation medal in architecture, brought Calhoun to lecture at the interdisciplinary programme of landscape architecture at the University of Pennsylvania. Calhoun hadn’t always talked of mice while thinking of men, but by the mid-1970s, results from his studies over the previous 25 years led him to believe he had a moral responsibility to do so.
Film producers and writers of fiction and nonfiction clamped on to Calhoun’s ideas and incorporated them into their own work. Page after page of Tom Wolfe’s 1968 book The Pump House Gang – published on the same day as his The Electric Kool-Aid Acid Test – paid homage to Calhoun’s idea of a behavioural sink. Calhoun’s work, in part, led one of the writers of Catwoman to introduce the character Ratcatcher to the comic strip. The bestselling children’s book Mrs Frisby and the Rats of NIMH may have had its origin in Calhoun’s rat experiments. At the very least, Calhoun thought it did, based on a visit by the author, Robert Conly (who wrote under the pseudonym Robert C O’Brien), to his lab at NIMH. And the list goes on and on.
In perhaps the oddest twist of all, as early as the 1960s, Calhoun’s studies of mice and rats led him to devote a good deal of the later years of his career to working on the creation of a human “world brain”. “We are now at the critical transition to a new type of man,” Calhoun told an audience in 1969, “one which depends increasingly on extracortical prostheses to evolve and utilise concepts.” Calhoun was convinced that by linking together these extracortical prostheses – akin to today’s internet hubs – we might be able to harness creativity and, among other things, figure a way out of the overpopulation problem. Never one to shy away from bold prediction, Calhoun told this same audience that “a rough calculation indicates that by 40,000 years from now less than 5% of creative activity will be done by our cortex and at least 95% by prostheses”.
When Calhoun died of a heart attack and stroke he suffered while on holiday in 1995, the New York Times and Washington Post ran obituaries. Both described the behavioural sink (though they didn’t use the term), as well as rodent universes full of Beautiful Ones.
A 2017 Washington Post article described Calhoun as a man “who achieved the recognition attained by only a handful of other social scientists, such as Pavlov and Skinner”. Certainly, in the 60s and early 70s, Calhoun’s work generated tremendous attention. But the lasting impact of his work is nowhere near that of Pavlov’s work or Skinner’s work, which have shaped and continue to shape research programmes around the world and are discussed, at length, in nearly every psychology textbook, as well as many an animal-behaviour textbook (including my own). Indeed, in the grand scheme of things, Calhoun’s work has not fared well in the world of academia.
It’s true that, in its heyday, Calhoun’s work on rats and mice could also be found in animal-behaviour and psychology textbooks. But a review of textbooks in those fields today shows virtually no mention of Calhoun’s studies. And to find a discussion of Calhoun’s work in academic journals today is no easy matter either. While the historians Jon Adams and Edmund Ramsden have written a series of excellent papers that look at Calhoun’s work, those papers are published in journals such as Comparative Studies in Society and History and Journal of Social History – journals that researchers studying evolution, animal behaviour, population dynamics and psychology would rarely, if ever, read. On occasion, a PhD dissertation will still cite one or more of Calhoun’s studies, but these tend to be citations to show that the author has done their history homework rather than citations suggesting that Calhoun’s work helped shape the ideas in the dissertation. Web of Science, the leading citation index for scientific papers, shows that almost none of Calhoun’s papers are cited any more. The one exception is his 1973 paper Death Squared: The Explosive Growth and Demise of a Mouse Population, published in the Proceedings of the Royal Society of Medicine, which is still cited on occasion, although virtually never in a major animal behaviour or psychology journal.
Why has Calhoun’s work not fared well in the world of academia? For one thing, after he published his Death Squared study, Calhoun rarely published his results in mainstream science journals, and, indeed, many of his studies, including those on Universes 33 and 34 – in which he examined whether cooperation reduced explosive rates of population growth in his rodents (it did) – were never published at all. Word of those studies would only have spread through people who heard Calhoun lecture about them or read a mention of them in a review paper Calhoun wrote in his later years.
Calhoun’s sometimes glib use of anthropomorphic terminology has also hurt his standing in the world of science. Today, the sort of anthropomorphic language – “Beautiful Ones”, “universal autism”, “pied pipers”, “somnambulists”, and more – that Calhoun used to describe rodents, even in his most technical papers, is not just frowned upon but thought of as unprofessional, as well as dangerous. It’s difficult to imagine an editor of a major journal in animal behaviour, evolution or psychology allowing an author to describe extremely aggressive individuals as “berserk”, as Calhoun did. Anthropomorphism was frowned on at the time Calhoun was doing his experiments as well, but there was much more leeway. In a similar vein, while most scientists today and in Calhoun’s day would agree that behavioural and evolutionary work in nonhumans can inform our understanding of ourselves, the idea that a handful of studies in a small number of species could or should impact policy decisions is approached with much greater trepidation. But, in his papers and in his lectures, Calhoun would often slip into language that, at the very least, made it appear as if his policy recommendations did indeed stem largely from his work on two species of rodents.
In the field of animal behaviour, and to a lesser extent in psychology, another reason Calhoun’s work has fallen off the map is that there has been a significant shift in perspective toward detailed cost-benefit analyses in the study of nonhuman behaviour. Calhoun considered the costs and benefits of social behaviour in his universes, but he wasn’t all that concerned with directly measuring those costs and benefits or casting his work in an explicit, cost-benefit framework. For example, as opposed to the approach Calhoun took to the fighting that occurred in his rodent universes, a study of aggression today might measure the size of the combatants, the amount of energy expended on different types of fighting behaviour, the risk associated with different levels of fighting, the benefits linked to winning a fight, and more. Work on population dynamics and behaviour has also changed radically since Calhoun undertook his experiments.
Some scientists retain vivid recollections of Calhoun, his work, and its long-term impact (or lack thereof). When Stephen Suomi, who moved into Calhoun’s space at NIMH, looks back on the body of Calhoun’s work, he’s most impressed by one thing: “He anticipated,” Suomi says, “the cross-disciplinary integration necessary to really study complex developmental problems.” Powerful praise, indeed, for Calhoun the thinker. Neil Greenberg, an animal behaviourist who, as a postdoc, overlapped briefly with Calhoun at NIMH in the 1970s, casts Calhoun’s work as the sort of material that gets undergraduate students excited about the study of behaviour. “I ended up using some of his research as gee-whiz kind of stuff for teaching,” he says today.
Perhaps more than anything else, the reason references to Calhoun’s work on his rodent universes have plummeted in the scientific literature is because no evidence for the behavioural sinks, Beautiful Ones, or other observations that Calhoun detailed in his rat and mouse universes has been found in wild populations of animals – rat, mouse, or otherwise. Part of that is, no doubt, because for the past few decades, no one has been explicitly looking for these things when working in the field. But in the 70s and early 80s, most animal behaviourists in biology and psychology departments would have been familiar with Calhoun’s work, yet field studies then (and later) on population dynamics were not finding anything that resembled Calhoun’s conclusions.
Unlike its fate in the academy and its technical journals, thanks not only to Catwoman, The Pump House Gang, Mrs Frisby and the Rats of NIMH and the hundreds of newspaper articles that came out his work during his lifetime, but also to contemporary popular science articles, podcasts, and more, Calhoun’s work lives on in our collective consciousness and has remained a subject of fascination in popular culture. After all, how could the public not be endlessly fascinated with the US Senate discussing rodent utopias turned dystopias full of “Beautiful Ones” scampering about rodent apartment complexes? Or “pied piper” mice following around a researcher who told a collection of the best scientists in the world that his work may “sound like rantings of a mad egghead locked up in his ivory tower”, and who wanted to write a book called The Rodent Key to Human Survival?
This essay is adapted from Dr Calhoun’s Mousery: The Strange Tale of a Celebrated Scientist, a Rodent Dystopia and the Future of Humanity published by The University of Chicago Press.