The ethologist John B. Calhoun coined the term "behavioral sink" to describe the collapse in behavior which resulted from overcrowding. Over a number of years, Calhoun conducted over-population experiments on Norway rats (in 1958–1962) and mice (in 1968–1972). Calhoun coined the term "behavioral sink" in his February 1, 1962 report in an article titled Population Density and Social Pathology in Scientific American  on the rat experiment. Calhoun's work became used as an animal model of societal collapse, and his study has become a touchstone of urban sociology and psychology in general.
In the 1962 study, Calhoun described the behavior as follows:
Many [female rats] 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. ...
The common source of these disturbances became most dramatically apparent in the populations of our first series of three experiments, in which we observed the development of what we called a behavioral sink. The animals would crowd together in greatest number in one of the four interconnecting pens in which the colony was maintained. As many as 60 of the 80 rats in each experimental population would assemble in one pen during periods of feeding. Individual rats would rarely eat except in the company of other rats. As a result extreme population densities developed in the pen adopted for eating, leaving the others with sparse populations.
... In the experiments in which the behavioral sink developed, infant mortality ran as high as 96 percent among the most disoriented groups in the population.
Calhoun would continue his experiments for many years, but the publication of the 1962 article put the concept in the public domain, where it took root in popular culture as an analogy for human behavior.
While Calhoun was working at NIMH in 1954, he began numerous experiments with rats and mice. During his first tests, he placed around 32 to 56 rodents in a 10 x 14-foot case in a barn in Montgomery County. He separated the space into four rooms. Every room was specifically created to support a dozen matured brown Norwegian rats. Rats could maneuver between the rooms by using the ramps. Since Calhoun provided unlimited resources, such as water, food, and also protection from predators as well as from disease and weather, the rats were said to be in "rat utopia" or "mouse paradise", another psychologist explained.
Following his earlier experiments with rats, in 1972 Calhoun would later create his "Mortality-Inhibiting Environment for Mice": a 101-inch square cage for mice with food and water replenished to support any increase in population, which took his experimental approach to its limits. In his most famous experiment in the series, "Universe 25", population peaked at 2,200 mice and thereafter exhibited a variety of abnormal, often destructive behaviors. By the 600th day, the population was on its way to extinction.
Influence of the concept
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The 1962 Scientific American article came at a time at which overpopulation had become a subject of great public interest, and had a considerable cultural influence. The study was directly referenced in some works of fiction, and may have been an influence on many more.
Calhoun had phrased much of his work in anthropomorphic terms, in a way that made his ideas highly accessible to a lay audience. Tom Wolfe wrote about the concept in his article "Oh Rotten Gotham! Sliding Down into the Behavioral Sink", later to be made into the last chapter of The Pump House Gang. Lewis Mumford also referenced Calhoun's work in his The City in History, stating:
No small part of this ugly barbarization has been due to sheer physical congestion: a diagnosis now partly confirmed with scientific experiments with rats – for when they are placed in equally congested quarters, they exhibit the same symptoms of stress, alienation, hostility, sexual perversion, parental incompetence, and rabid violence that we now find in the Megalopolis.
Calhoun himself saw the fate of the population of mice as a metaphor for the potential fate of man. He characterized the social breakdown as a "spiritual death", with reference to bodily death as the "second death" mentioned in the Biblical book of Revelation 2:11.
Rat to human comparison
Controversy exists over the implications of the experiment. Psychologist Jonathan Freedman's experiment recruited high school and university students to carry out a series of experiments that measured the effects of density on behavior. He measured their stress, discomfort, aggression, competitiveness, and general unpleasantness. He declared to have found no appreciable negative effects in 1975. Researchers argued that "Calhoun's work was not simply about density in a physical sense, as number of individuals-per-square-unit-area, but was about degrees of social interaction."
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- NLM Announces the Public Release of the Papers of John B. Calhoun, U.S. National Library of Medicine, 2013-10-13.
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- Lewis Mumford, The City in History, 1961, p 210. cited in Theodore D. Fuller, et al. "Chronic Stress and Psychological Well-being: Evidence from Thailand on Household Crowding," Social Science Medicine, 42 (1996): 267
- Garnett, Carla. (2008). Plumbing the ‘Behavioral Sink’, Medical Historian Examines NIMH Experiments in Crowding.. NIH Record. Retrieved 2013-07-07.