Simon Ings

What rats can teach us about the dangers of overcrowding

John Calhoun’s startling experiments in the mid-20th century showed that once rodents reach a certain density they behave entirely selfishly – and the population collapses

A war on rats in Watford, December1943. Over the course of a month more than a million rats were killed with poisoned titbits laid in runs and sewers. Credit: Mirrorpix via Getty Images

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