On July 9, 1968, John Calhoun began his mouse experiment called Universe 25. He designed the perfect mouse habitat of 16 buildings each divided into 16 apartments with their own feeding stations. A plentiful supply of food and water was always available. No predators or diseases. The ideal temperature and humidity. Two male and two female mice were placed in Universe 25 on that July day. Calhoun and his team then watched what happened over a nearly four year period (New Scientist, Dec. 14, 2024).