In the late 1960s, American ethologist John B. Calhoun set out to create a utopia. His “Universe 25” experiment was meant to study the effects of overpopulation in a world where every basic need was met. Inside a meticulously designed enclosure, mice had unlimited food, water, shelter, and no predators. In theory, they had everything they needed to thrive. Instead, a disturbing collapse of society unfolded, revealing profound insights into social behavior—both in rodents and, potentially, in humans.
At the start, Universe 25 seemed like a paradise. Eight mice—four males and four females—were introduced into the enclosure. With abundant resources, their population doubled every 55 days. The mice exhibited normal social behaviors, forming family structures and raising their young in harmony. The colony’s population surged, reaching over 2,000 mice. But as the numbers grew, cracks in their society began to show.
Despite the availability of resources, the sheer density of the population triggered unexpected changes. Male mice became increasingly aggressive, engaging in violent fights for dominance. Others withdrew, avoiding social interactions altogether. Female mice, overwhelmed by constant pregnancies and competition, began neglecting or even attacking their offspring. The natural order that had once governed their community unraveled, giving rise to chaos and dysfunction.
A peculiar subgroup of mice emerged among the chaos—Calhoun called them “the beautiful ones.” These mice isolated themselves from the rest, dedicating their time exclusively to grooming, eating, and sleeping. They showed no interest in socializing, mating, or engaging in the typical behaviors needed for survival. Though they appeared physically pristine, their detachment from society signaled a deeper decay. With reproduction dwindling and social bonds dissolving, the colony’s fate was sealed.
Calhoun coined the term “behavioral sink” to describe this downward spiral of societal breakdown. As birth rates plummeted and aggressive behaviors escalated, the colony’s population peaked at 2,200 before beginning its steep decline. By the experiment’s end, no new mice were being born, and the population had dwindled to extinction. Universe 25 had failed—not due to a lack of resources but because of deep-rooted social dysfunction.
Calhoun believed Universe 25 held valuable lessons for human societies, particularly in urban settings. Overcrowded cities today face rising levels of social isolation, anxiety, and stress—issues that eerily resemble the mice’s behavioral collapse. Loneliness is becoming a public health crisis, with more people struggling to form meaningful connections despite living in densely populated areas. Meanwhile, declining birth rates in many developed nations mirror the reproductive struggles observed in Universe 25.
The experiment also sparks discussion about marginalized communities. The LGBTQ+ community, for example, continues to face high rates of social isolation, discrimination, and violence. Much like the “beautiful ones” who withdrew from society, LGBTQ+ individuals often find themselves excluded or struggling to fit into traditional social structures. Discrimination and mental health challenges exacerbate this isolation, making it harder for them to thrive despite living in societies that claim to be progressive.
The haunting implications of Universe 25 extend beyond just mice. In modern cities, loneliness is skyrocketing, mental health disorders are at an all-time high, and fertility rates are declining. Many factors contribute to these trends—economic struggles, social disconnection, and digital isolation among them. While human societies are far more complex than rodent colonies, the eerie similarities suggest that unchecked urbanization and social fragmentation could lead to profound consequences.
What can we learn from Universe 25? The experiment suggests that abundance alone isn’t enough to sustain a thriving society. Humans, like mice, need social bonds, purpose, and a sense of belonging. As urban populations swell and technology reshapes human interactions, fostering meaningful connections and addressing mental health challenges should be a priority. Otherwise, we risk following in the footsteps of Universe 25—a society that had everything but ultimately lost its will to survive.