sixpenceee:

Calhoun’s Mouse Utopia

In July 1968, ethologist John B. Calhoun built a “mouse utopia,” a metal enclosure 9 feet square with unlimited food, water, and nesting material. He introduced four pairs of mice, and within a year they had multiplied to 620. 

But after that the society began to fall apart males became aggressive, females began neglecting their young, and the weaker mice were crowded to the center of the pen, where resources were scarce. By January 1973 the whole colony was dead.

Calhoun felt that his experiment held lessons as to the potential dangers of human overpopulation, and he urged his colleagues to study the effects of high population density on human behavior. (Source)