Nearly fifty years ago an American ethologist studied the apocalyptic effects of overpopulation in laboratory rats. This very interesting experiment can be paralleled with the evolution of human society.
An incredible experiment
On July 9, 1968, ethologist John B. Calhoun began an experiment at the National Institute of Mental Health (NIMH) in Bethesda, Maryland, USA. This consisted of placing eight mice in an open-top box measuring 1.30 meters high and 2.50 meters wide. The interior was ideal as it was a comfortable climate and food and water was easily accessible. There was also plenty of room and no predators on the horizon.
This study named Univers 25 was the latest in a series of the same type conducted by the researcher. At the end of his experiment, John B. Calhoun then published a detailed article in the journal Proceedings of the Royal Society of Medicine in January 1973.
An impressive decline
The “rat paradise” quickly became an overcrowded “city”. Four months after the beginning of the experiment (October 1968), the first generation of newborns arrived and then the population doubled every two months. If everything seemed to be going well in the beginning, however it obviously did not last.
In August 1969, the population reached 620 rats. And more than a year and a half after the beginning of the experiment, the maximum population reached: 2200 rats. A few weeks later, newborns were no longer able to survive. However the experiment did not end until 1973 – after a long and chaotic decline.
Lasting effects on their behaviour
The groups of female rats that managed to escape the general cannibalism that happened in Universe 25 – remained marked forever. At the end of the experiment, John B. Calhoun transferred these female rats into a new normal social environment, but they were not able to do anything but eat and sleep.
A reference in psychology
This experience confirms what John B. Calhoun was already talking about in another study called Population Density and Social Pathology in 1962, a period when urbanism was increasing. However, this research on the social consequences of overpopulation is still regarded today as a classic experiment, which has changed psychology and revolutionized urban sociology.