Next month is the 30th anniversary of the death of the American ethologist John B. Calhoun. In the early 1960s, he created an series of experiments to discover the causes of social dysfunction. His most famous work involved a so-called ‘rat utopia’ in which rodents were provided comfortable living quarters with unlimited food, water and warmth, and protection from predators. In this cosy environment, the only bar to ratty heaven was that space was limited.

Nonetheless, the happy rats bred prodigiously until their quarters became uncomfortably overcrowded. This lack of space meant they were unable to control with whom or how often they came into social contact. Routine acts like feeding, grooming, nest-building and rearing young were all interrupted by an abundance of social contact.

When

See Full Page