Darwinian natural selection could help halt human "mad cow disease", experts say after finding a tribe impervious to a related fatal brain disorder.
The Papua New Guinea tribe developed strong genetic resistance after a major epidemic of the CJD-like disease, kuru, spread mostly by cannibalism.
Medical Research Council experts assessed more than 3,000 survivors of the mid-20th Century epidemic.
Their findings appear in the New England Journal of Medicine.
Kuru, a prion disease similar to CJD in humans and BSE in animals, was transmitted at mortuary feasts where - until the practice was banned in the late 1950s - women and children consumed their deceased relatives as a mark of respect and mourning.
But a gene variation, G127V, found in people from the Purosa valley region of the Eastern Highlands seems to offer high or even complete resistance to the disease .
And experts believe this could be the strongest example yet of recent natural selection in humans.
MRC Prion Unit director Professor John Collinge said: "It's absolutely fascinating to see Darwinian principles at work here.
"This community of people have developed their own biologically unique response to a truly terrible epidemic.
"The fact that this genetic evolution has happened in a matter of decades is remarkable.
"Kuru comes from the same disease family as CJD, so the discovery of this powerful resistance factor opens up new areas for research taking us closer to understanding, treating and hopefully preventing of a range of prion diseases."
University College London's Institute of Neurology geneticist Professor John Hardy said the findings were fascinating.
"It's fantastic demonstration of natural selection.
"Because people who have this mutation were protected from this fatal disease their proportion in society increased massively."
But he said a similar resistance to CJD would be less likely to develop.
He said: "In Papua New Guinea kuru became the major cause of death, so there was a clear survival advantage and the selection pressure was enormous.
"Here in Britain the numbers with CJD are very small and so the selection pressures will be less."