A new genetic study suggests that prehistoric humans often suffered from a fatal neurodegenerative disease spread by the consumption of human flesh. The finding, which seems to suggest that cannibalism was once common, will be controversial, as some anthropologists think the practice has always been rare.
Researchers first came across the disease, called kuru, in the Fore, an isolated group of people in New Guinea. Some 40 years ago, kuru killed almost 10% of the Fore, who allegedly ate parts of their dead. This flesh transmitted the disease, which is caused by a malformed protein called a prion. Contorted prions cause other, native proteins to misfold, clump together, and kill brain cells. A similar process causes Creutzfeldt-Jakob disease (CJD) in humans and mad cow disease.
A decade ago, John Collinge of University College London (UCL) showed that people carrying two identical copies of the gene for the prion protein are more susceptible to developing CJD than people who carry two unmatched gene variants. In a report online in Science this week, Collinge, UCL's Simon Mead, and their colleagues confirm that these variants protect against kuru and show that they exist in people throughout the world.
Collinge's team looked at DNA from the Fore and also from 1000 people representing other groups around the world. All ethnic groups examined carried two versions of the prion gene. Among the Fore, the fraction of women carrying one copy of each variant--so-called heterozygotes--instead of two copies of one or the other, was particularly high. His group found that 23 of the 30 women over age 50--the few people left who were old enough to have practiced cannibalism--were heterozygotes, whereas statistically only 15 were expected. This would only happen if the presence of both genes improved an individual's fitness, such as by protecting against kuru, he notes.
There is a chance that epidemics of prion diseases arose from eating tainted meats--just as beef from cows with mad cow disease can be a source of CJD. But it is more likely that humans were the main source of prion-tainted tissue, says Collinge. Adriano Aguzzi, a molecular biologist at the University Hospital of Zürich, agrees: “Collinge [has] derived the disturbing conclusion that cannibalism was commonplace among our ancestors,” he says. “Consequently prion diseases, now exceedingly rare, may have ravaged human populations in the distant past.” Fossil evidence supports the idea that cannibalism was once common, Collinge adds, although some researchers aren't convinced.