Inside Universe 25

Inside Universe 25

From Discovery by BBC World Service

April 20, 2026 · 27 min

About this episode

The episode explores John Calhoun's research on the effects of overcrowding in rodent populations and its implications for human society.

“I shall largely speak of mice,” the paper begins “but my thoughts are on man.” So begins a truly extraordinary scientific paper, and an equally extraordinary story. “Death Squared: The Explosive Growth and Demise of a Mouse Population.” was published in 1973 by John Calhoun, and it detailed his increasingly bizarre research into the psychological effects of overcrowding. Over two decades he built a series of ‘rodent utopias’, where he could keep a population of rats or mice, meet all their basic food and shelter needs, but mess around with population levels. He wanted to see how they responded to having to live, cheek-by-tiny-jowl, with far more other rats than they were used to. And it wasn’t pretty. Social orders melted into chaos, rodents fought indiscriminately, or shut themselves away at the top of the enclosure. Mating orders collapsed, population numbers tanked, and eventually, every single rat was dead. His work came at a prescient time. In the 60s and 70s, the exponentially expanding human population was a hot-button topic, and ‘population panic’ was in full swing. Alongside the expansion of cities, creeping urban sprawl, rising city-centre crime rates and 'urban…

Topics covered

  • overcrowding
  • psychological effects
  • population dynamics
  • urban living
  • rodent behavior

Keywords

  • overcrowding
  • John Calhoun
  • rodent utopias
  • population collapse
  • urban sprawl

Mentioned in this episode

Books & works: Death Squared: The Explosive Growth and Demise of a Mouse Population

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