On July 9, 1968, John Calhoun began his mouse experiment called Universe 25. He designed the perfect mouse habitat of 16 buildings each divided into 16 apartments with their own feeding stations. A plentiful supply of food and water was always available. No predators or diseases. The ideal temperature and humidity. Two male and two female mice were placed in Universe 25 on that July day. Calhoun and his team then watched what happened over a nearly four year period (New Scientist, Dec. 14, 2024).
Within 18 months the population had increased to 2200, a number at which normal behaviour began to collapse. One of the first symptoms was a “pathological togetherness”—the mice began to cluster around a few feeders, leaving the others unattended. Then on the 600th day the population began to crash. Males became either hyper aggressive or withdrawn, listless and sexually inactive. Mating courtship declined. The females exhibited almost no maternal care. As the population declined further, most social interactions ended, and the surviving mice spent most of their time grooming themselves and eating. By this time the population had declined to 121, and this trajectory continued until the last mouse died before the experiment reached its four year anniversary.
The findings of Universe 25 with mice confirmed a similar study by Calhoun between 1958 and 1962 using Norway rats. Much the same aberrant behaviour occurred with the rats in their “utopian” conditions. When the population reached about 200, they would gather together in large assemblies, but would rarely eat as isolated individuals. Like the mice, the rat females had trouble holding their litters to term, and their lack of maternal care caused many pups to die—mortality rates reached as high as 96%. The rat males became aggressive, cannibalistic or reclusive.
Mice and rats have been used in all kinds of test situations, but not in anything quite comparable to these social experiments. And Calhoun’s presentation of Universe 25 to the Royal Society of Medicine in June 1972 caused quite a stir, particularly because the symposium was called “Man in His Place”. As Calhoun explained, “I shall largely speak of mice, but my thoughts are on man, on healing, on life and its evolution.” His earlier rat experiment also caused some serious consideration about the sociological implications for humans.
Half of humanity now lives in cities, in population densities that are comparable to the mouse and rat conditions when their social structure began to collapse—about 70% of humans are expected to be urban dwellers by 2050.
We are not mice and rats, but both of Calhoun’s experiments do raise some interesting questions about how our behaviour changes as populations rise. Do we have optimum living conditions beyond which our behaviour starts to become aberrant? What is that number? Do we actually have to reach that number, or can social media create the same kind of psychological and sociological disturbances? Many developed countries, where humans live in “utopias” comparable to mice and rats in their enclosures, are now experiencing reproduction declines that are not sufficient to maintain the national populations. We may attribute this to affluence, but is some other more basic mammalian dynamic at play? And drug use. Is this, along with the fentanyl disaster, symptomatic of the social breakdown that occurs with too many people existing in too confined a space without the natural challenges that impart meaning to each individual life? Does mass media have the same effect as having too many people crammed together with no escape from each other?
These questions do not diminish the tragedy of each individual death or dysfunction. But such questions do inspire some sociological speculation about what is a healthy human population, how much affluence do we really need, are challenges necessary to keep societies viable, and do we consciously and subconsciously have wars to counteract the disintegration of societies? Are such questions even practical or sensible to consider?
Thinking in this direction might help us consider how to build cities, manage population densities, provide public spaces, design amenities, construct communities, and formulate Official Community Plans. More awareness about what we are doing and why we are doing it should be helpful in constructing healthy societies and protecting nature. What are the ingredients that make a healthy population and lifestyle? Does the behaviour of mice and rats in their “utopias” have any bearing on what we should be thinking and doing?
Ray Grigg for Sierra Quadra
Links of Interest:
- Death Squared: The Explosive Growth and Demise of a Mouse Population – By John B Calhoun (1973)
- What Humans Can Learn From Calhoun’s Mice Utopia – Victor
- This Old Experiment With Mice Led to Bleak Predictions For Humanity’s Future By Rudy Molinek, Smithsonian Magazine (2015)
- Articles about, or mentioning, overpopulation
Top image credit: Mice sleeping by the water fount – Photo by
Rene Schwietzke via Flickr (CC BY 2.0)
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