![]() ![]() Referenced far outside of the fields of ecology and mental health, Calhoun's rats have-or certainly had-come to seem part of the common cultural stock, shorthand for the problems of urban crowding just as Pavlov's dogs were for respondent conditioning. The macabre spectacle of crowded psychopathological rats and the available comparisons with human life in the densely-packed inner cities ensured that the experiments were quickly adopted as "scientific evidence" of social decay. (4) Like Pavlov's dogs, Calhoun's rats came to assume a near-iconic status as emblematic animals, exemplary of the ways in which behavioral experimentation at once marks and violates the human-animal distinction. (3) It has since been included as one of "Forty Studies that Changed Psychology," joining papers by such figures as Freud, Pavlov, Milgram, Rorschach, Skinner, and Watson. That paper, "Population Density and Social Pathology," went on to be one of the most widely cited in psychology. At a certain density, they had ceased to act like rats and mice, and the change was permanent.Ĭalhoun published the results of his early experiments with the rats at NIMH in a 1962 edition of Scientific American. The crowded rodents had lost the ability to co-exist harmoniously, even after the population numbers once again fell to low levels. Unable to breed, the population plummeted and did not recover. They were the majority in the late phases of growth, existing as a vacant, huddled mass in the centre of the pens. ![]() Subordinate animals withdrew psychologically, surviving in a physical sense but at an immense psychological cost. In certain sections of the pens, infant mortality rose as high as 96%, the dead can nibalized by adults. Mothers neglected their infants, first failing to construct proper nests, and then carelessly abandoning and even attacking their pups. Others became pansexual and hypersexual, attempting to mount any rat they encountered. Some males became exclusively homosexual. Males became aggressive, some moving in groups, attacking females and the young. As the pens heaved with animals, one of his assistants described rodent "utopia" as having become "hell." (2) The only restriction Calhoun imposed on his population was of space-and as the population grew, this became increasingly problematic. With no predators and with exposure to disease kept at a minimum, Calhoun described his experimental universes as "rat utopia," "mouse paradise." With all their visible needs met, the animals bred rapidly. What had happened?Įmployed in the Laboratory of Psychology of the National Institute of Mental Health from 1954, and later as Chief of the Unit for Research on Behavioral Systems in the Laboratory of Brain, Evolution and Behavior until 1986, Calhoun repeated the experiment in specially constructed "rodent universes." Using a variety of strains of rats and mice, he once more provided his populations with food, bedding, and shelter. (1) Be that as it may, a population of only 150 seemed surprisingly low. That the predicated maximum was never reached ought to come as no surprise: 5000 rats would be tight indeed. ![]() Instead, the population levelled off at 150, and throughout the two years Calhoun kept watch, never exceeded 200. What Calhoun built was quarter acre pen, what he called a "garden of eden," and, as the population expanded from a few individuals to many, a "rat city." Calhoun calculated that the habitat was sufficient to accommodate as many as 5000 rats. Calhoun would later reflect that his neighbor probably expected a few hutches, perhaps a small run. Calhoun's neighbor agreed to let him build a rat enclosure on disused woodland behind his house in Towson, Maryland.
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