John Calhoun

John Calhoun

John B. Calhoun's famous rodent habitat studies documented that even while providing all requirements for a population, stress (which he induced through overcrowding) will always lead to extinction, with notable exhibition of bizarre and self-defeating behaviors along the way, and especially towards the end of the habitat's cycle. As modern living, and in particular the looming climate crisis, create ever greater stress in our own habitat, consideration of whether Calhoun's findings apply to our current situation may well be in order. A few articles are listed below. More at

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In pioneering rat research, a warning for human society
He designed elaborate colonies for the creatures that became a kind of paradise, free of predators and disease, with an unlimited supply of food. But paradise soon became a crowded hell, and that's why his work half a century ago has had such a profound impact on our understanding of humans. Calhoun, a research psychologist at the National Institute of Mental Health for 40 years, discovered that severe crowding produced horrific behavioural changes among animals. The changes were so profound that social order broke down, and ultimately the entire rodent population collapsed. His findings led to the concept of the "behavioural sink" and suggested that evolution had given animals, perhaps including humans, an innate and irreversible self-destruct button to prevent a species from overpopulating its habitat ... A 1962 edition of Scientific American on the early results of his experiments became one of the most widely cited papers in psychology.

The urban animal: population density and social pathology in rodents and humans
Calhoun placed several rats in a laboratory in a converted barn where - protected from disease and predation and supplied with food, water and bedding - they bred rapidly. The one thing they were lacking was space ... Unwanted social contact occurred with increasing frequency, leading to increased stress and aggression. Following the work of the physiologist, Hans Selye, it seemed that the adrenal system offered the standard binary solution: fight or flight. But in the sealed enclosure, flight was impossible. Violence quickly spiralled out of control ... Their numbers fell into terminal decline and the population tailed off to extinction ... At the experiments’ end, the only animals still alive had survived at an immense psychological cost: asexual and utterly withdrawn, they clustered in a vacant huddled mass. Even when reintroduced to normal rodent communities, these “socially autistic” animals remained isolated until death. In the words of one of Calhoun’s collaborators, rodent “utopia” had descended into “hell”.

Death Squared: The Explosive Growth and Demise of a Mouse Population by John B Calhoun MD
Proceedings of the Royal Society of Medicine Volume 66 January 1973
John Calhoun's presentation on Universe 25 (one of his last) and what this might mean for humans. "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. 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. 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."


"It is difficult to get a man to understand something, when his salary depends on his not understanding it." (Upton Sinclair)
However, "The good thing about science is that it's true whether or not you believe in it." (Neil deGrasse Tyson)

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