I learned about John Calhoun's Mouse Utopia experiment from this Youtube video. The corresponding 1962 paper isn't readily available.

What I want to know is, did Calhoun account for genetic diversity in his experiment? Apparently he started with only a few breeding pairs, all white lab mice.

  • $\begingroup$ Could you cite the paper? I'd rather not go watch movies. $\endgroup$
    – AliceD
    Apr 14, 2017 at 20:42
  • $\begingroup$ @AliceD - Oh yeah, duh. I think this was the one. (Wikipedia has a bibliography in its article on John B. Calhoun.) ncbi.nlm.nih.gov/pubmed/13875732 $\endgroup$ Apr 15, 2017 at 0:31
  • $\begingroup$ The 1962 Paper is available through Scribd or Jstor or directly from Scientific American $\endgroup$ Feb 25, 2018 at 12:20
  • $\begingroup$ @Chris - Great, thanks. I'll check it out. $\endgroup$ Feb 25, 2018 at 16:33

1 Answer 1


Quick (short answer)

No, Calhoon did not account for genetic diversity in his experiments outlined in your question.

Full answer

Reading the article you mentioned, Calhoun (1962) started with wild Norway Rats, also referred to as common rats, brown rats, street rats, sewer rats, or Hanover rats.

I confined a population of wild Norway rats in a quarter-acre enclosure. 'With an abundance of food and places to live and with predation and disease eliminated or minimized, only the animals' behavior with respect to one another remained as a factor that might affect the increase in their number. There could be no escape from the behavioral consequences of rising population density. By the end of 27 months the population had become stabilized at 150 adults. Yet adult mortality was so low that 5,000 adults might have been expected from the observed reproductive rate. The reason this larger population did not materialize was that infant mortality was extremely high. Even with only 150 adults in the enclosure, stress from social interaction led to such disruption of maternal behavior that few young survived.

Then he turned to a domesticated albino strain of the Norway rat under more controlled circumstances indoors, and

The data for the present discussion come from the histories of six different populations. Each was permitted to increase to approximately twice the number that my experience had indicated could occupy the available space with only moderate stress from social interaction. In each case my associates and I maintained close surveillance of the colonies for 16 months in order to obtain detailed records of the modifications of behavior induced by population density.

There is very little genetic variation in brown rats (Ness, et al. 2012), no matter where in the world you collect them (Ness, 2013). Therefore, apart from the fact that the article was discussing data on a domesticated albino strain of the Norway rat, all the experiments mentioned used brown rats. There were no black rats, mole rats, or any other kinds of rat used.


Calhoun, J.B. (1962). Population density and social pathology. Scientific American, 206, 139—48.

Ness, R. W., Zhang, Y.-H., Cong, L., Wang, Y., Zhang, J.-X., & Keightley, P. D. (2012). Nuclear Gene Variation in Wild Brown Rats. G3: Genes|Genomes|Genetics, 2(12), 1661—1664.
DOI: 10.1534/g3.112.004713 PMCID: PMC3516487

Ness, R. (2013). Genetic diversity of wild brown rats [Online]
Retrieved from: http://sites.utm.utoronto.ca/ness/blog/01182016-1515/genetic-diversity-wild-brown-rats

  • $\begingroup$ I must have misunderstood the question, as I thought the OP was asking if the results of the experiment could have been accounted for by inbreeding, which I think would have required a review of the genetic variation typically used in similar experiments (which I suspect is similar to this one, so the answer would have been "yes"). Anyways, good answer, and glad the OP is happy with it. $\endgroup$
    – Arnon Weinberg
    Feb 26, 2018 at 18:20

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