A few decades ago, John Calhoun, an expert in animal behaviour, set up an experiment involving eight white mice. He put them in what we can call ‘mouse heaven’.  On day one of the experiment, the four male and four female mice got moved into a large, spacious tank with an endless supply of food.

The tank was nicely designed with 16 stairwells, each leading to numerous nesting boxes large enough to hold 15 mice. The tank also had walls that the mice could climb and tools to keep themselves entertained. The temperature inside the tank was stable, the environment was controlled and predators were kept out. Life was nice. This little mouse hotel had everything a mouse could want.

So, initially, these eight mice had the privilege of occupying a tank with enough space and resources for 3,840 mice. As expected, they soon started making babies, and at first, the mouse population doubled every 55 days. During this time, the mice lived in relative peace and harmony. However, by the end of year one, when the population had increased to 620, this perfect mouse society started to crack.