The first experiments were made between 1947 and 1951 using 32 to 56 Norwegian rats in a 10×14-foot case in a barn. As the rats were provided with food, water, nesting materials and protection from predators it was called "Utopia". The case was divided in four interconnected rooms able to hold a dozen rats each. With time, the rats started to show bizarre conducts. Some of the behaviors observed included:
- Some dominant males made harems, having control over several female rats to mate.
- Some females made groups and created their own territories living together and violently rejecting any male approaching, with no apparent interest in breeding.
- Of those that did breed, strange behaviors started to show, like violently attacking the infants (this is not uncommon, for some reason rodents sometime eat their offspring) or stopped caring for the offspring long before it was normal. Those who survived were often unprepared themselves to care for their own offspring once they had them.
- High infant mortality rate.
- Some males still tried to mate even if that caused them to suffer violence from stronger males.
- Sporadic and unexplained violence. Some males were frequent recipients of violence that they had to endure because there was no escape.
- Homosexual behavior in some males.
- Some rats just kept isolated from the rest, not interacting with them nor trying to mate, dedicating most of their time to grooming. These were called "the beautiful ones" precisely because they spent a lot of time cleaning themselves.
- Cannibalism.
