Published online 11 April 2003 | Nature | doi:10.1038/news030407-13

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Our ancestors had brains - for dinner

Spread of disease-protection genes points to cannibalistic past.

Funeral feasts used to put the Fore people at risk of contracting Kuru.Funeral feasts used to put the Fore people at risk of contracting Kuru.© Corbis

Our ancestors may have eaten each other's brains.

A new study has found genes that offer protection from prion diseases, such as Creutzfeldt-Jakob Disease (CJD), in populations on four continents. This spread might be an evolutionary response to the dangers of cannibalism.

The safeguarding DNA is most common among the Fore people of Papua New Guinea. This is the legacy of the Fore's custom of eating their dead relatives in funereal feasts. Last century, cannibalism triggered an epidemic of a deadly brain disease called kuru.

"This is the signature of natural selection in a population where there's been a devastating recent epidemic due to cannibalism," says team member Simon Mead of University College London. Seeing the same signature in other parts of the world suggests that diseases may once have spread by the same route, he says.

Kuru and CJD are thought to occur when misshapen prion proteins warp other healthy prions and clump together in the brain.

About one in a million people develop CJD spontaneously. Others have caught it by eating infected tissue, as seems to have happened in the spread of mad cow disease to cause variant CJD in humans. It's thought that the Fore caught kuru around the turn of the twentieth century from eating a sufferer of spontaneous CJD.

The prion gene comes in several types, and we have two copies. People with two different versions are less likely to develop CJD or kuru, and have a longer incubation time when they do. People with identical genes are more vulnerable.

Nearly 80% of Fore women aged over 50, who had participated in funereal feasts, had the protective gene, Mead's team found1 - only women and children ate their ancestors. Women born after cannibalism was banned in the mid-1950s were less likely to carry the gene.

Mead's team also looked at Africans, Asians and Europeans. All carried some form of protective mutation. "The genes are more common than you'd expect," says Mead. This suggests that epidemics of prion disease have struck throughout history, he says.

Human bones bearing marks of butchery are seen as evidence of cannibalism among Neanderthals, and among early modern humans who lived in Spain 800,000 years ago. Archaeologists have also found faeces and cooking pots from twelfth-century America containing human muscle protein.

But evidence of cannibalism in modern humans is scant, and dates back only about 15,000 years, points out archaeologist Nick Thorpe of King Alfred's College in Winchester, UK.

"Most archaeologists and anthropologists would accept that there has been cannibalism," says Thorpe. "But it's much more difficult to know how common it has been." He suspects the practice has been widespread but rare, appearing and dying out many times.

The key thing to find out, says Thorpe, is how common cannibalism would need to be for the genetic variant to arise. Mead says that his study can't answer this, nor the question of when or where the protective genes arose. "It has to have been before recorded history," he says. 

  • References

    1. Mead, S. et al. Balancing selection at the prion protein gene consistent with prehistoric kurulike epidemcis. Science, published online, doi:10.1126/science.1083320 (2003). | PubMed |