"Behavioral sink" is a term invented by ethologist John B. Calhoun to describe a collapse in behavior which can result from overcrowding. The term and concept derive from a series of over-population experiments Calhoun conducted on Norway rats between 1958 and 1962. In the experiments, Calhoun and his researchers created a series of "rat utopias" – enclosed spaces in which rats were given unlimited access to food and water, enabling unfettered population growth. 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. He would later perform similar experiments on mice, from 1968 to 1972.
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.
While Calhoun was working at NIMH (National Institute of Mental Health) 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, Calhoun would later create his "Mortality-Inhibiting Environment for Mice" in 1972: a 101-inch by 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. (The page John B. Calhoun contains more detail about this experiment).
The specific voluntary crowding of rats to which the term 'behavioral sink' refers is thought to have resulted from the earlier involuntary crowding: individual rats became so used to the proximity of others while eating that they began to associate feeding with the company of other rats. Calhoun eventually found a way to prevent this by changing some of the settings and thereby decreased mortality somewhat, but the overall pathological consequences of overcrowding remained.
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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.
Applicability to humans
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."
- Hall, Edward, T. (1966). The Hidden Dimension: An Anthropologist Examines Humans' Use of Space in Public and in Private. Anchor Books. p. 25. ASIN B0006BNQW2.
- "Population Density and Social Pathology" (PDF). Scientific American. Retrieved 2015-12-14.
- Calhoun, John B. (1962). "Population density and social pathology". Scientific American. 206 (3): 139–148. doi:10.1038/scientificamerican0262-139 (inactive 31 May 2021). PMID 13875732.CS1 maint: DOI inactive as of May 2021 (link)
- Hock, Roger R. (2004). Forty Studies that Changed Psychology : Explorations into the History of Psychological Research (5th ed.). Prentice Hall. ISBN 978-0-13-114729-4.
- Calhoun, J. B. (1970). "Population density and social pathology". California Medicine. 113 (5): 54. PMC 1501789. PMID 18730425.
- NLM Announces the Public Release of the Papers of John B. Calhoun, U.S. National Library of Medicine, 2013-10-13.
- "The Behavioral Sink". Cabinet Magazine. Summer 2011. Retrieved 2012-08-24.
- Medical Historian Examines NIMH Experiments in Crowding Archived 2013-03-27 at the Wayback Machine, nih record, 2013-10-13.
- Calhoun, J. B. (1973). "Death squared: The explosive growth and demise of a mouse population". Proceedings of the Royal Society of Medicine. 66 (1 Pt 2): 80–88. doi:10.1177/00359157730661P202. PMC 1644264. PMID 4734760.
- Ramsden, Edmund and Jon Adams. 2009. Escaping the Laboratory:The Rodent Experiments of John B. Calhoun & Their Cultural Influence, p.22. 
- Ramsden, Edmund; Adams, Jon (2009). "Escaping the Laboratory: the rodent experiments of John B. Calhoun & their cultural influence" (PDF). Journal of Social History. 42 (3): 761–797. doi:10.1353/jsh/42.3.761.
- Moore, Adam (2010). Privacy rights moral and legal foundations. University Park, Pa: Pennsylvania State University Press. p. 48. ISBN 978-0271036861.
- 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.
- Fessenden, Marissa 2015, How 1960s Mouse Utopias Led to Grim Predictions for Future of Humanity, Smithsonian Magazine.
- What Humans Can Learn From Calhoun's Rodent Utopia, Victor.