Social Breakdown and Overpopulation - a study with mice

I don't know how I ended up finding this - but here's an interesting study from 1978 that that creates a closed ecosystem of mice that removes most external threats and resource limits and studies what happens when overcrowding conditions develop. Here's the link to the paper: Death Squared by John B. Calhoun. The study documents the social breakdown of the mice, who eventually lose ability to properly socially interact and maintain their social structures. The entire group of mice was on the way to extinction when the study ended despite a top population of over 2000 mice from early in the study. The contrast of instinctual and learned behaviors are far fuzzier than I would've expected. At the end, even when removed from the crowded conditions remaining mice were socially unable to form a social order and/or reproduce. They had been biologically "broken" absent proper socialization throughout their lives.