This is one of the most enlightening works concerning the depths of human nature, so all available information has been collected here.

Eight mice given perfect living conditions with everything they needed. The population rose, fell and became extinct within 4 years. It was repeated several times using mice and rats and the results were the same:

A social experiment involving mice which should have the same impact on humanity as the apple falling on Newton's head. Unfortunately, this has not happened due to... unknown factors or probably due to politics.

Fig. The number of mice in the Calhoun's experiment

1. The original study of John Calhoun:

John B. Calhoun, "Death Squared: The Explosive Growth and Demise of a Mouse Population" Proc. roy. Soc. Med. Volume 66 January 1973, pp80-88

[Original copy of this work at http://www.ncbi.nlm.nih.gov]

2. Description in Wikipedia [2014.05.25]:

In July 1968 four pairs of mice were introduced into the Utopian universe. The universe was a 9-foot (2.7 m) square metal pen with 54-inch-high (1.4 m) sides. Each side had four groups of four vertical, wire mesh "tunnels". The "tunnels" gave access to nesting boxes, food hoppers, and water dispensers. There was no shortage of food or water or nesting material. There were no predators. The only adversity was the limit on space.

Initially the population grew rapidly, doubling every 55 days. The population reached 620 by day 315, after which the population growth dropped markedly. The last surviving birth was on day 600. This period between day 315 and day 600 saw a breakdown in social structure and in normal social behavior. Among the aberrations in behavior were the following:

expulsion of young before weaning was complete,

wounding of young,

inability of dominant males to maintain the defense of their territory and females,

aggressive behavior of females,

passivity of non-dominant males with increased attacks on each other which were not defended against.

[Wikipedia 2014.05.25]

3. Transcript from the film Mouse Utopia Experiment on Youtube:

In a unique experiment that took years to complete, Doctor Calhoun used white mice to study population growth and its effects on individual behaviour.

In this sixteen cell mouse habitat, utopian conditions of nutrition, comfort and housing were provided for the potential population of over three thousand mice. [...] Factors which normally control population growth such as predation by owls and cats were eliminated. Transmissible disease were also reduced. In effect, the mouse universe simulated the present situation of the continually expanding population of humans.

To see how Dr Calhoun's mouse universe grew, we use the familiar population graph again. Within the first one hundred days, the mice went through the period Dr Calhoun called, "strive". This was the period of adjustment. Territories were established and nests were made. The next period lasted about two hundred and fifty days. The population of the mice doubled every sixty days. This was called the "exploit" period. The use of resources become unequal. Although each living unit was identical in structure and opportunities, more food and water was consumed in some areas. As the population increased, most mice associated eating and drinking with the presence of others. And crowding developed in certain units. The third period, consisting of three hundred days, found the population of mice leveling off. This was called the "equilibrium" period. Dr Calhoun noticed that the newer generations of young were inhibited, since most space was already socially defined.

At this time, some unusual behaviour become noticeable. Violence become prevalent. Excess males strived for acceptance, were rejected and withdrew. Huddling together, they would exhibit brief flurries of violence amongst themselves. The effects of violence became increasingly visible. Ceratin individuals became targets of repeated attacks. These individuals would have badly chewed and scarred tails. Other young mice growing into adulthood exhibited an even different type of behaviour. Dr Calhoun called these individuals "the beautiful ones". Their time was devoted solely to grooming, eating and sleeping. They never involved themselves with others, engaged in sex, nor would they fight. All appeared as a beautiful exhibit of the species with keen, alert eyes and a healthy well-kept body. These mice, however, could not cope with unusual stimuli. Though they looked inquisitive they were, in fact, very stupid.

Dr Calhoun called the last period the "die" phase, leading the population into extinction. Although the mouse utopia could house 3000, the population began to decline at 2200. In the shift from the equilibrium to the die phase, each animal became less aware of associates, despite all animals being pushed closer together. Dr Calhoun concluded that the mice could not effectively deal with the repeated contact of so many individual. The evidence of violence increased to the point where most individuals had had their tails bitten to some degree. Eventually, the whole mouse population perished.

[...]

The larger the population, the less care a mother gives to her nest and young.

4. Part-transcript from the film "Critical mass":

Link to the most important part of the movie "Critical mass" conected with the Calhoun's experiment.