In 1962, a strange epidemic swept through several communities in Tanganyika, present-day Tanzania. It wasn’t a virus, but laughter among teenage schoolgirls. The contagious laughter, which lasted for about two and a half years, afflicted about 1,000 people and forced at least 14 schools to temporarily shut down.
Experts later determined that the origin of the epidemic was psychological, perhaps related to stress caused by the presence of British colonialism. But such events have raised scientific questions about why humans can’t control behaviors such as laughing, yawning, coughing and shivering — and why they spread among groups of people.
“We are a part of a human herd whose behavior is often the involuntary playing out of an ancient neurological script that is so familiar that it goes unnoticed,” wrote neuroscientist Robert Provine in his book, "Curious Behavior."