John Bumpass Calhoun (; May 11, 1917 – September 7, 1995) was an American ethologist and behavioral researcher noted for his studies of population density and its effects on behavior. He claimed that his observations of the bleak effects of overpopulation on rodents were a grim preview for the future of the human race. During his studies, Calhoun coined the terms "behavioral sink" to describe aberrant behaviors in overcrowded situations, and "beautiful ones" to characterize passive individuals who withdraw from all social interaction under extreme population density.
Calhoun's work gained worldwide recognition. He spoke at international conferences and his opinion was sought by groups as diverse as NASA and the District of Columbia's panel on overcrowding in local jails. His rat and mouse studies were a basis for the development of Edward T. Hall's ideas on proxemics.: "Anthropologists also turned to Calhoun's work. Calhoun had kept in touch with Edward Hall.... Since their first meetings, Hall's ideas on proxemics—the relation between people and physical space—had become widely known, and in 1966, he published a popular book on the topic: The Hidden Dimension: An Anthropologist Examines Man's Use of Space in Public and Private. Calhoun's seminal 1962 Scientific American article on "Population Density and Social Pathology" fueled fears of the dystopian effects of human overpopulation, which Paul Ehrlich predicted in his 1968 bestseller The Population Bomb. This article was published in the October 2024 print edition with the title, "The Population Bomb That Wasn't".
Early life and education John Calhoun was born May 11, 1917, in the tiny rural town of Elkton, Tennessee. His parents were James Calhoun, a high school principal who rose through the ranks of the Tennessee Department of Education; and Fern Madole Calhoun, a kindergarten teacher. John had three siblings: an older sister, Polly; and two younger brothers, Billy and Dan. When John was still an infant, the Calhouns moved from Elkton to Winchester, Tennessee. After he completed kindergarten (taught by his mother), the family moved to the small rural town of Brownsboro, Tennessee. John would later refer to himself as a "Tennessee country boy".
In 1930, when John was 13, his father was promoted to the Tennessee school board, and the family relocated to Nashville. Shortly after, John began attending meetings of the Tennessee Ornithological Society. Amelia Laskey, distinguished for her work in bird banding and in the study of the chimney swift, was a pivotal influence on his developing interest in birds and bird habits. John spent much of his junior and senior high school years banding birds and observing their behavior.
Despite his father's refusal to help him attend an out-of-state university, John made his way to the University of Virginia where he obtained a bachelor's degree in biology in 1939. In his third year in 1938, he published his first scientific paper, titled "Swift Banding at Nashville and Clarksville"; it appeared in The Migrant, the journal of the Tennessee Ornithological Society. Over the summer, he worked for Alexander Wetmore, head of the Smithsonian Institution in Washington, D.C., doing ornithology research. Calhoun attended graduate school at Northwestern University where he earned an M.S. in biology, and a Ph.D. in ethology in 1943. His dissertation was on the activity rhythms of two rodents, prairie voles and Hispid cotton rats.: His dissertation was titled, "An Analysis of the Locomotor Activity Rhythms of Two Ecologically Equivalent Rodents, Microtus ochrogaster (Wagner) and Sigmodon hispidus hispidus Say and Ord".
While at Northwestern University, Calhoun met Edith Gressley, an undergraduate biology major. They married in 1942. They had two daughters together and remained married until the end of Calhoun's life.
Career Early rat studies After graduating from Northwestern, Calhoun taught at Emory University and Ohio State University. In 1946, he and Edith moved to Towson, Maryland, a suburb of Baltimore. Calhoun worked on the Rodent Ecology Project at Johns Hopkins University. The project was testing a new poison that would kill rats in downtown Baltimore. When the poison lost its efficacy, the project's leader, Johns Hopkins Professor David E. Davies, and his young assistant John Calhoun, noticed that the rats seemed to have a self-regulating mechanism that capped their population at about 150 rats per city block. Calhoun wanted to understand how the mechanism worked, and suggested an experiment to do so.
In March 1947, he began a 28-month study of a colony of nocturnal Norway rats in a outdoor pen. Even though five females over this time-span could theoretically produce 5,000 healthy progeny for this size pen, Calhoun found that the population never exceeded 200 individuals, and stabilized at 150.: "Calhoun calculated that his enclosure should be able to accommodate thousands of rats, but their numbers never rose above two hundred. It was social pressure rather than the availability of resources, he concluded, that acted as a natural check on the population." Moreover, the rats were not randomly scattered throughout the pen area, but had organized themselves into twelve or thirteen local colonies of a dozen rats each. He noted that twelve rats seemed to be the optimal number that can live harmoniously in a natural group, beyond which stress and psychological effects function as group break-up forces.: "What Calhoun's equations suggest is that the optimal group size in mammals should often, though not always, be about twelve, as in his rats."
In Calhoun's next posting, at Jackson Laboratory in Bar Harbor, Maine, in 1951, he once more studied a colony of Norway rats. During this period, his first daughter, Catherine "Cat" Calhoun, was born. The family was living at the time in the guesthouse on the Luquer estate.
In late 1951, the Calhouns moved back to Silver Spring, Maryland. He worked for Walter Reed Army Medical Center in the neuropsychiatry division before gaining a position in 1954 at the National Institutes of Health, where he would be employed for the next 32 years. 1954 was also when his second daughter, Cheshire Calhoun, was born.
Norway rat experiments Calhoun pursued his experiments in rodent behavior, using domesticated Norway rats, at his lab on the second floor of a huge barn on the Casey farm outside Rockville, Maryland. The area is now a suburban center but the barn still stands, renovated for suburban usage. In the days of Calhoun's occupancy, there was a small, cluttered office area at the top of the stairs. The rodent odor was said to be overpowering, and it took some time before one could breathe normally.
The research area was divided into three parts. In the center section, a box-like room was built. There was a hallway all the way around the box, and stairs that led to the top of it. The box was divided into four rooms, or habitats, . Each room had a door for a researcher or caretaker to enter by, and in the ceiling of each room was a glass window. The activity in each room could be observed through these windows. Each room was divided into quarters by partitions. V-shaped ramps connected pens I and II, II and III, and III and IV. Pens I and IV were not connected. Mounted on the wall in the corner of each quarter was an artificial burrow, which could be accessed via a spiral staircase. In two of the quarters, the "burrows" were from the floor, and in the other two the "burrows" were from the floor. Each quarter also contained a drinking station and a feeding station. These variations in environment led to differences in behavior patterns and ultimately to the concept of "behavioral sinks".
The research carried on in this lab (labeled the "Casey Barn") began in 1958 and lasted until 1962. In that year, he published a monograph, The Ecology and Sociology of Norway Rats. It was unusual then to associate the word "sociology"—normally reserved for the study of humans—with animal subjects, but it indicated Calhoun's growing belief that his rodent colonies could shed light on the social problems of humans. In July 1962, he temporarily moved his family to California after he accepted a one-year fellowship at the Center for Advanced Study in the Behavioral Sciences in Palo Alto.
In 1956, Calhoun had joined an informal think tank organized by psychiatrist Leonard Duhl, who worked at the National Institute of Mental Health (NIMH). The think tank's full name was the Committee to Explore the Influence of Physical Social Environmental Variables as Determinants of Mental Health, but its 17 members dubbed themselves "Space Cadets" because of their interest in how physical space affected well-being. The members had diverse specializations including architecture, city planning, physics, biology and mathematics. For more than a decade, the Space Cadets met two or three days each year, and the lively exchange of ideas stimulated Calhoun's thinking. It prompted him to question the existing literature on population growth in animals and humans. With help from his mathematician colleagues, Calhoun constructed a new statistical model to predict the level of "social welfare" in a rodent colony. The model's three key variables were: "the number of animals interacting with one another, the time between when an animal ended one social interaction and when it began another (the 'refractory' period), and the size of the space in which social interactions took place."
Mouse experiments
In the early 1960s, NIMH acquired rural property outside Poolesville, Maryland. The facility that was built on the property housed several research projects, including those headed by Calhoun. It was here that he conducted his landmark experiments with mouse universes, the most famous of which was called "Universe 25". In July 1968, four pairs of mice were introduced into the habitat, which was a square metal pen with sides. Each side had four groups of four vertical, wire mesh "tunnels". The "tunnels" gave access to nesting boxes, food hoppers, and water dispensers. There was no shortage of food or water or nesting material. There were no predators. The only adversity was the limit on space.
Initially, the population grew rapidly, doubling every 55 days. The population reached 620 by day 315, after which the population growth dropped markedly, doubling only every 145 days. The last surviving birth was on day 600, bringing the total population to a mere 2200 mice, even though the experiment setup allowed for as many as 3840 mice in terms of nesting space. This period between day 315 and day 600 saw a breakdown in social structure and in normal social behavior. Among the aberrations in behavior were the following: expulsion of young before weaning was complete, wounding of young, failing to engage in sexual approaches, inability of dominant males to maintain the defense of their territory and females, aggressive behavior of females, passivity of non-dominant males with increased attacks on each other which were not defended against.
After day 600, the social breakdown continued and the population declined toward extinction. Females ceased to reproduce. Their male counterparts withdrew completely, never engaging in courtship or fighting, and only performing tasks essential to their health. They ate, drank, slept, and groomed themselves – all solitary pursuits. Sleek, healthy coats and an absence of scars characterized these males. Breeding never resumed and behavior patterns were permanently changed.