In a 1962 edition of Scientific American, the ecologist John B Calhoun presented the results of a macabre series of experiments conducted at the National Institute of Mental Health (NIMH).1He had 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, a fact that became increasingly problematic as what he liked to describe as his “rat city” and “rodent utopia” teemed with animals. 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.2 But in the sealed enclosure, flight was impossible. Violence quickly spiralled out of control. Cannibalism and infanticide followed. Males became hypersexual, pansexual and, an increasing proportion, homosexual. Calhoun called this vortex “a behavioural sink”. 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the experiments’ end, the only animals still alive had survived at an immense psychological cost: asexual and utterly withdrawn, they clustered in a vacant huddled mass.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”.3
Calhoun’s experiments with rats and mice proved extremely influential. His findings resonated with a variety of concerns, including population growth, environmental degradation and urban violence.
Population density and social pathology:
The consequences of the behavioral pathology we observed were most apparent among the females. Many were unable to carry pregnancy to full term or to survive delivery of their litters if they did. An even greater number, after successfully giving birth, fell short in their maternal functions. Among the males the behavior disturbances ranged from sexual deviation to cannibalism and from frenetic overactivity to a pathological withdrawal from which individuals would emerge to eat, drink and move about only when other members of the community were asleep. The social organization of the animals showed equal disruption. Each of the experimental populations divided itself into several groups, in each of which the sex ratios were drastically modified. One group might consist of six or seven females and one male, whereas another would have 20 males and only 10 females.
The conclusions drawn from this experiment were that when all available space is taken and all social roles filled, competition and the stresses experienced by the individuals will result in a total breakdown in complex social behaviours, ultimately resulting in the demise of the population.