Author: Karl Smallwood / Source: Today I Found Out
In 1968, an expert on animal behaviour and population control called John B. Calhoun built what was essentially a utopia for mice that was purpose built to satisfy their every need. Despite going out of his way to ensure the inhabitants of his perfect mouse society never wanted for anything, within 2 years virtually the entire population was dead.
So what happened?Dubbed “Universe 25”, Calhoun’s mouse utopia was built with the needs of its mouse inhabitants firmly in mind and was designed specifically to cater to their every whim. Containing plentiful food, water, bedding and, at least initially, space, the enclosure was described as follows:
A tank, 101 inches square, enclosed by walls 54 inches high. The first 37 inches of wall was structured so the mice could climb up, but they were prevented from escaping by 17 inches of bare wall above. Each wall had sixteen vertical mesh tunnels—call them stairwells—soldered to it. Four horizontal corridors opened off each stairwell, each leading to four nesting boxes. That means 256 boxes in total, each capable of housing fifteen mice.
Well versed in rodent populations from dozens of previous experiments (something that’s kind of apparent when you realise the enclosure was called Universe 25) Calhoun anticipated that his mouse paradise could reliably and more importantly, comfortably house 3840 mice. Before that though, he needed to pick the proverbial Adam and Eve of his mouse Garden of Eden. Calhoun eventually settled on four breeding pairs of mice specially bred for the experiment and hand-picked from the most healthy specimens from the National Institute of Health’s own breeding colony.
Before discussing what happened next we should give some background information about how this experiment came to be and what it was hoping to accomplish. Prior to creating Universe 25, Calhoun had performed a number of similar experiments with rodents starting way back in the 1940’s, all of which ended in failure when the population either stalled or turned on itself.
For example, in one experiment Calhoun created an enclosure that could have easily housed 5000 rats but the eventual population never rose above 200 despite unlimited food, water and a complete absence of predators or threats. Furthermore Calhoun noticed that, again despite ample space his rodents would often crowd together, which resulted in a breakdown of social structure amongst the population. This unusual phenomenon led Calhoun to coin the phrase “Behavioural Sink” to describe what he felt was the inevitable collapse of any overpopulated society.
Calhoun’s experiments eventually caught the eye of the National Institute of Mental Health or NIMH who were intrigued about the observed effects of overpopulation in rodents, specifically if any of the observed phenomenon could be applied to humans. To this end, NIMH gave Calhoun access to a small piece of land they owned in Maryland and the funding…
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