![]() ![]() Ramps connected pen 1 to pen 2, 2 to 3, and 3 to 4, but not pen 1 to pen 4. These pens contained everything a rat could possibly need: food, water, elevated burrows, winding staircases, nest boxes… a rodent wonderland. With extremely high rates of infant mortality, by the end of the 27th month of observation the population had stabilised at 150 adults.Ĭalhoun and his team were surprised by these unexpected results and so embarked on a more controlled experiment involving a population of domesticated Norway rats, conducted in a converted barn (a step up in luxury for the animals).Ĭalhoun’s new rat palace consisted of a 3m x 4.3m room, divided into four pens by an electrified fence. Universe 25 was his research pinnacle – a “rodent utopia”.Ĭalhoun calculated that his pen of wild Norway rats (or brown rats, aka Parisian rats, Hanover rats, street rats, common rats, sewer rats, wharf rats… in essence, “rats” as you know them) could have a sustainable density of 5000, but the population strangely never exceeded 200. But he’s become recently spotlit for his work in 1958–62, starting with a quarter-acre pen of wild Norway rats, and a 1968–72 experiment with mice called Universe 25. His work spans six decades, from early experiments with rodents in the 1940s to his death in 1995. John B Calhoun was a behavioural researcher and ethologist who spent the largest part of his career at the US National Institute of Mental Health (NIMH), in Maryland. The two studies, over a total of eight years, aimed to explore the effects of population density on behaviour. What I didn’t know at the time was that it was inspired by a series of experiments on population dynamics from the 1940s to the 1970s. Fris by and the Rats of NIMH as a young’un. In a 2011 article, Ramsden writes that Calhoun’s studies were brandished by others to justify population control efforts largely targeted at poor and marginalized communities.I first read Mrs. Population growth in the 1970s was swelling, and films such as Soylent Green tapped into growing fears of overpopulation and urban violence. “There’s no recovery, and that’s what was so shocking to ,” says Ramsden.Ĭalhoun wasn’t shy about anthropomorphizing his findings, binning rodents into categories such as “juvenile delinquents” and “social dropouts,” and others seized on these human parallels. Effectively, says Ramsden, they became “trapped in an infantile state of early development,” even when removed from Universe 25 and introduced to “normal” mice. Instead of interacting with their peers, males compulsively groomed themselves females stopped getting pregnant. Mice born into the chaos couldn’t form normal social bonds or engage in complex social behaviors such as courtship, mating, and pup-rearing. ![]() This iteration, dubbed Universe 25, was the first crowding experiment he ran to completion.Įventually Universe 25 took another disturbing turn. The only scarce resource in this microcosm was physical space, and Calhoun suspected that it was only a matter of time before this caused trouble in paradise.Ĭalhoun had been running similar experiments with rodents for decades but had always had to end them prematurely, ironically because of laboratory space constraints, says Edmund Ramsden, a science historian at Queen Mary University of London. In 1968, Calhoun had started the experiment by introducing four mouse couples into a specially designed pen-a veritable rodent Garden of Eden-with numerous “apartments,” abundant nesting supplies, and unlimited food and water. ![]() The results, laid bare at his feet, had taken years to play out. Calhoun wasn’t the survivor of a natural disaster or nuclear meltdown rather, he was a researcher at the National Institute of Mental Health conducting an experiment into the effects of overcrowding on mouse behavior.
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