In the late 1960s, the psychologist John B. Calhoun built Universe 25, a mouse enclosure with plenty of food, water and nesting space but limited room. The mouse population grew until crowding led to a breakdown of normal behavior, which Calhoun called the behavioral sink. Aggression, cannibalism and the neglect of young spread, and eventually the population collapsed. The few surviving mice, which he called the Beautiful Ones, avoided conflict by never developing the complex adult behaviors of courtship, mating and defending territory, so the population could not recover. The experiment became a famous model of how social stress and overcrowding can damage a society even when resources are plentiful.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.