For centuries, the Fore people of Papua New Guinea participated in a morbid funeral ritual. When one of the tribesmen died, his wife, sisters, and daughters would dismember him limb by limb, then eat his brain as a sign of respect. In the 20th century, the Fore began suffering from kuru—a brain disease that resembles mad cow (Creutzfeldt-Jakob) disease.
More than 2,500 Fore died before researchers realized that ingesting human brains could cause the disease. Yet some Fore never developed kuru and seemed to be resistant to it. Scientists believed that a genetic mutation might have protected these Fore.
Simon Mead of the University College of London and his colleagues compared DNA samples from 152 Fore who died of kuru and 3,000 living Fore. More than 700 of the Fore in the sample participated in eating human brains before the practice was banned in the 1950s. The researchers found a variant of PRNP, the gene that makes prions. With kuru, malformed prions develop, causing a chain reaction that transforms the brain into a mush. A variation on codon 129, dubbed G127V, protected about 51 Fore from being susceptible to kuru. None of the 152 known kuru sufferers carried the variation.
"I hope it will become a textbook example of how evolution happens," Mead says. This anti-kuru gene shows how the human body adapts to protect itself from impending danger.