Cannibalism, asexuality and violence, a society that had collapsed. What's going on here? In 1972, John B. Calhoun detailed the specifications of a utopia designed for mice, built in the laboratory. Every aspect of Universe 25, as this particular model was called, was designed to cater for the well-being of its rodent residents, increased their lifespan and allowed them to mate. There was abundant food, water and nesting material. The Universe was cleaned regularly. There were no predators, the temperatures stable, paradise. Or maybe not. Four pairs of disease-free mice selected from the National Institute of Health's Elite Breeding Colony moved in on day one. It took months for the rodents to familiarise themselves with their new world. Then they started to reproduce and the population increased exponentially, doubling every 55 days. Those were the good times in paradise. Past day 315, more than 600 mice now lived in Universe 25, rubbing shoulders on their way up and down the stairwells to eat, drink and sleep. Population growth slowed. Young ones found themselves born into a world with far more mice than meaningful social roles. Males faced a lot of competitors to defend their territory against. Many found that so stressful they gave up. Normal discourse within the community broke down and with it the ability of mice to form social bonds. Loan females retreated to isolated nesting boxes on penthouse levels. Other males, a group Calhoun termed the beautiful ones, never sought sex and never fought. They just ate, slept and groomed, wrapped in narcissistic introspection. Elsewhere, cannibalism, asexuality and violence became endemic, mouse society had collapsed. On day 560, the population peaked at 2,200 mice. A few mice survived past weaning until day 600, after which there were few pregnancies and no surviving young. As the population had stopped regenerating itself, its path to extinction was clear. The mice had lost the capacity to rebuild their numbers. Many that could still conceive such as the beautiful ones and their secluded singleton female counterparts had lost the social ability to do so. On day 920 was the last conception. The last mouse died on May 23rd 1973, four years and ten months after colonization. Calhoun later said that the creatures had died two deaths. The first was that of their spirit and their society. The second death was that of their physical body. It was not the first time the ethylogist had built a world for rodents. Calhoun had been creating utopian environments for rats and mice since the 1940s with consistent results. Overpopulation leads to explosive violence and hypersexual activity, followed by asexuality, self-destruction and extinction. In his widely cited paper, Population Density and Social Pathology, Calhoun concluded, no matter how sophisticated we are, once the number of individuals capable of filling social roles greatly exceeds the number of such roles, only violence and disruption can follow. He then referred to a phenomenon he called Behavioral Sink. Behavioral Sink is our desire to be in the presence of others, to be conditioned to seek to be near others, and to be drawn to the crowd, in spite of the conflicts that this can generate. Drawing from Calhoun's popular research, social scientists started to call for restrictions on reproduction as the only possible response to the world's rising population. Calhoun himself was more optimistic about our future. He argued, as our physical space declines, we are forced to extend a conceptual space, our network of ideas and technologies. Later in his career, he turned to possible solutions and began to build creative universes that minimise the ill effects of overcrowding. What are your thoughts? Is overcrowding a danger for mankind or does it only affect rodents? And if so, what can save the human psyche? Avoiding eye contact in crowded places is one strategy, but is that enough? To read more about Universe 25 and its cultural impact, read the paper of Edmund Ramstone and John Adams. You'll find a link in the description below. If you like how we explain complicated ideas in simple cartoon animation, you can support us. Visit patreon.com slash sprouts. Just visit us, learn how it works and what's in it for you. We hope to see you there. And if you are a parent or educator, check out our website Sproutschools.com. There you can find this and other video lessons, additional resources and classroom activities.