> In the late 1960s, US scientist John B Calhoun created a ‘Mouse Utopia’ – an artificial environment which provided what he regarded as the perfect breeding conditions. To everyone’s amazement, and without any signs of disease or hardship; **after a few months of rapid population growth**, the mouse colony ceased to reproduce at all; and soon became extinct – every single mouse dying within three years.
Biggest question: Since the conditions were not changed, and the population was growing while low, why did it not grow again after the deaths shrank it back to the starting size?
In: Biology
His whole experiment had a poor study design, so it can’t really be considered science, and we can’t draw any conclusions from it.
Because of the social and psychology effects that was engraved into the rats. Even those who survived exhibited the same traits.
The death of the rats is caused by several factors, but all of them lead to the declining future generations. Inability to raised the youngs, fewer births, social behavior, and unsimilar traits to the original rats ultimately sealed their fate.
https://en.m.wikipedia.org/wiki/Behavioral_sink
Ignore my previous comment if anyone read it, I was very incorrect.
Basically the tl;Dr for OP’s question is that overpopulation conditions in animals (such as rats and mice) with social order of some kind results in disorientation in individuals there in, and causes pathological behavior changes ranging from mild deviations from what would be called normal such as self-isolation and failure of maternal instinxts, to severe and extreme deviations such as cannibalism and unprovoked aggression.
Don’t think follow-up studies have been done, but this experiment was primarily observation. We know what happened, but you’d need some serious additional controls to get at a why. Without another (hopefully more rigorous) series of experiments, I don’t think anyone is going to be able to point you to a cause.
As others have noted, epigenetics, learned behavior, and other factors may come into play here. Here’s [a fun study](https://royalsocietypublishing.org/doi/full/10.1098/rsos.170121) on how rats learn. Tl;dr is that rats aggressively pattern their thought processes based on behaviors they observe.
Not all creatures behave the same.
Mice are simple minded creatures. They couldn’t adapt to unlimited food. They ended up becoming extreme in their conduct.
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