Behavioral sink

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"Behavioral sink" is a term invented by ethologist John B. Calhoun to describe a collapse in behavior that can result from overpopulation. The term and concept derive from a series of over-population experiments Calhoun conducted on Norway rats between 1958 and 1962.[1] In the experiments, Calhoun and his researchers created a series of "rat utopias"[2] – enclosed spaces where rats were given unlimited access to food and water, enabling unfettered population growth. Calhoun coined the term "behavioral sink"[3] in a February 1, 1962, Scientific American article titled "Population Density and Social Pathology" on the rat experiment.[4] He would later perform similar experiments on mice, from 1968 to 1972.[5]

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.[6]


In the 1962 study, Calhoun described the behavior as follows:

Many [female rats] were unable to carry the 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.[4]

Calhoun's early experiments with rats were carried out on farmland at Rockville, Maryland, starting in 1947.[7]

While Calhoun was working at the National Institute of Mental Health (NIMH) in 1954, he began numerous experiments with rats and mice. During his first tests, he placed around 32 to 56 rats in a 10-by-14-foot (3.0 m × 4.3 m) cage 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",[8] another psychologist explained.[9]

Following his earlier experiments with rats, Calhoun later created his "Mortality-Inhibiting Environment for Mice" in 1968: a 101-by-101-inch (260 cm × 260 cm) cage for mice with food and water replenished to support any increase in population,[10] which took his experimental approach to its limits. In his most famous experiment in the series, "Universe 25",[11] population peaked at 2,200 mice even though the habitat was built to tolerate a total population of 4000. Having reached a level of high population density, the mice began exhibiting a variety of abnormal, often destructive, behaviors including refusal to engage in courtship, and females abandoning their young. By the 600th day, the population was on its way to extinction. Though physically able to reproduce, the mice had lost the social skills required to mate.[7]

Calhoun retired from NIMH in 1984, but continued to work on his research results until his death on September 7, 1995.[12]


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.[13]

Further, 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."[14] "Social density" appears to be key.

Applicability to humans[edit]

Calhoun had phrased much of his work in anthropomorphic terms, in a way that made his ideas highly accessible to a lay audience.[7]

Calhoun himself saw the fate of the population of mice as a metaphor for the potential fate of humankind. He characterized the social breakdown as a "spiritual death",[10] with reference to bodily death as the "second death" mentioned in the Biblical verse Revelation 2:11.[10]

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 human behavior. He measured their stress, discomfort, aggression, competitiveness, and general unpleasantness. He declared to have found no appreciable negative effects in 1975.[15]

The 1962 Scientific American article came at a time when overpopulation had become a subject of great public interest, and had a considerable cultural influence.[16] However, such discussions often oversimplified the original findings in various ways. It should however be noted that the work has a more differentiated message than, for example, Paul Ehrlich's now widely disputed[17][18][19] book The Population Bomb. Calhoun's worries primarily concerned a human population surge as an early stage, such as even more so a potentially independent increase in urbanization, soon after rendering much of a given society functionally sterile. Here, one moves from some modality of over- towards a much more irredeemable underpopulation. Now, while urban populations have long been noted to have lower fertility than their rural counterparts,[20] growing use of especially digital media is likely to end up depressing rural population growth as well.[21] And while this, today, still primarily concerns elite population decline, as some find highly deleterious in itself,[22] the aforementioned modalities of positive feedback in social diffusion may have Calhoun's empirical predictions apply to a much wider segment of society as well. For one, all this seems to hold up in the case of South Korea's unsustainably low total fertility rate, having already led to societal aging comparable with Calhoun's final cohort.

See also[edit]


  1. ^ 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.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ "John B. Calhoun and his Rat Utopia". DemystifySci. 2020-07-22. Retrieved 2024-05-08.
  3. ^ "Behavioral Sink definition | Psychology Glossary |". Retrieved 2024-05-08.
  4. ^ a b Calhoun, John B. (1962). "Population density and social pathology" (PDF). Scientific American. 206 (3): 139–148. doi:10.1038/scientificamerican0262-139 (inactive 31 January 2024). PMID 13875732. Archived (PDF) from the original on 2019-11-21. Retrieved 2015-12-14.{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link)
  5. ^ Ramsden, Edmund; Adams, Jon (2009). "Escaping the Laboratory: The Rodent Experiments of John B. Calhoun & Their Cultural Influence". Journal of Social History. 42 (3): 761–792. ISSN 0022-4529.
  6. ^ 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.
  7. ^ a b c "The Behavioral Sink". Cabinet Magazine. Summer 2011. Archived from the original on 2020-02-15. Retrieved 2012-08-24.
  8. ^ "Mouse Heaven or Mouse Hell?". Science History Institute. Retrieved 2024-05-08.
  9. ^ Medical Historian Examines NIMH Experiments in Crowding Archived 2013-03-27 at the Wayback Machine, nih record, 2013-10-13.
  10. ^ a b c 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.
  11. ^ "Universe 25, 1968–1973". The Scientist Magazine®. Retrieved 2024-05-08.
  12. ^ NLM Announces the Public Release of the Papers of John B. Calhoun Archived 2018-09-11 at the Wayback Machine, U.S. National Library of Medicine, 2013-10-13.
  13. ^ Ramsden, Edmund and Jon Adams. 2009. Escaping the Laboratory:The Rodent Experiments of John B. Calhoun & Their Cultural Influence, p.22. [1] Archived 2021-03-28 at the Wayback Machine
  14. ^ Garnett, Carla. (2008). Plumbing the 'Behavioral Sink', Medical Historian Examines NIMH Experiments in Crowding. Archived 2020-08-15 at the Wayback Machine. NIH Record. Retrieved 2013-07-07.
  15. ^ Freedman, Jonathan (November 1975). "Population density and pathology: Is there a relationship?". Journal of Experimental Social Psychology. 11 (6): 539–552. doi:10.1016/0022-1031(75)90005-0.
  16. ^ 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. Archived (PDF) from the original on 2019-11-21. Retrieved 2019-08-12.
  17. ^ Gooderham, Mary; Toronto, University of. "Debunking the 'population bomb'". Retrieved 2024-02-21.
  18. ^ Follett, Chelsea (January 5, 2023). "Defuse the Population Bomb Narrative before It's Too Late". Cato Institute. Retrieved February 21, 2024.
  19. ^ Haberman, Clyde (2015-05-31). "The Unrealized Horrors of Population Explosion". The New York Times. ISSN 0362-4331. Retrieved 2024-02-21.
  20. ^ Jaffe, A. J. (1942). "Urbanization and Fertility". American Journal of Sociology. 48 (1): 48–60. doi:10.1086/219078. ISSN 0002-9602. JSTOR 2769969. S2CID 144416655.
  21. ^ Population, National Research Council (US) Committee on; Casterline, John B. (2001), "Mass Media and Fertility Change", Diffusion Processes and Fertility Transition: Selected Perspectives, National Academies Press (US), retrieved 2024-02-21
  22. ^ Spandrell (March 26, 2013). "Lee Kuan Yew drains your brains for short term gain". Bloody shovel. Archived from the original on 11 October 2015. Retrieved February 21, 2024.

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