> 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
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.
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