He claimed that the bleak effects of overpopulation on rodents were a grim model for the future of the human race.

He spoke at conferences around the world and his opinion was sought by groups as diverse as NASA and the District of Columbia's Panel on overcrowding in local jails.

Calhoun's rat studies were used as a basis in the development of Edward T. Hall's 1966 proxemics theories.

His father was a high school principal who rose to a position in administration in the Tennessee Department of Education.

[citation needed] Calhoun's family moved from Elkton to Brownsville, Tennessee, and finally to Nashville, when[when?]

[citation needed] At this time, Calhoun began attending meetings of the Tennessee Ornithological Society.

[citation needed] Calhoun met his future wife, Edith Gressley, at Northwestern where she was a biology major and a student in one of his classes.

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.

[citation needed] While posted at Jackson Lab in Bar Harbor, Maine, Calhoun continued studying the Norway rat colony until 1951.

[citation needed] Calhoun pursued his experiments in behavior, using domesticated Norway rats, at his lab on the second floor of a huge barn on the Casey farm in the country outside Rockville, MD.

[citation needed] The research carried on in the lab on Casey's farm began in 1958 and lasted until 1962, when Calhoun was invited to spend a year at The Center for Advanced Study in the Behavioral Sciences in Stanford, California.

[citation needed] In the early 1960s, the National Institute of Mental Health (NIMH) acquired property in a rural area outside Poolesville, Maryland.

[1] His study has been cited by writers such as Bill Perkins as a warning of the dangers of living in an "increasingly crowded and impersonal world".

[4] Others took different lessons; medical historian Edmund Ramsden has hypothesized that the mouse society fell from excessive social interaction, rather than density per se.

Edmund Ramsden described one of Calhoun's experiments in which rats were placed in a sealed enclosure: "At the experiments' end, the only animals still alive had survived at an immense psychological cost: asexual and utterly withdrawn, they clustered in a vacant huddled mass [...] In the words of one of Calhoun's collaborators, rodent "utopia" had descended into 'hell'.

"Calhoun's phrase "behavioral sink" was sometimes used by others in reference to perceived urban moral degradation.

Alan Grant, co-creator of the dystopian Judge Dredd character, has acknowledged Calhoun's work as an influence.

Ramsden believes Calhoun's work may have influenced other apocalyptic fiction as well, including Soylent Green.

[6] His papers were donated to the National Library of Medicine by Edith Calhoun and the American Heritage Center.