Mouse utopia experiment john calhoun11/4/2023 ![]() 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.
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