It is a MV genetic marker that keeps protein from mutating in "mad human disease". I don't have the article that averaged out to half the population.
Cannibalism's DNA Trail: Gene may signal ancient prion-disease outbreaks
Bruce Bower
Cannibalism among prehistoric humans may have left lasting genetic marks, a team of scientists contends. Their controversial argument hinges on a link between specific DNA mutations and a disease that afflicted South Pacific villagers who practiced cannibalism as late as 1950.
Gene variations that protect against prion diseases?deadly neurological illnesses caused by proteins known as prions (SN: 10/11/97, p. 229)?frequently occur in modern human populations, say John Collinge of University College London and his colleagues. These variations occur in the gene that encodes a protein that's usually harmless but causes prion disease when it's in a mutant form. The protective variations originated around 500,000 years ago and spread via natural selection because they protect against epidemics of prion diseases, Collinge's team contends in an upcoming issue of Science.
Prion diseases include Creutzfeldt-Jakob disease in people and mad cow disease. These maladies unfold when prions, presumably from meat consumption, induce their harmless versions to assume the prions' warped shapes and then to clump together. This process leads to brain degeneration and death.
The potential link of protective genes to cannibalism stems from studies of a prion ailment known as kuru, which Fore villagers in Papua New Guinea contracted from 1920 to 1950 as a result of eating human brains and other tissue during funeral rituals. Enough prehistoric cannibalism occurred to have instigated kurulike epidemics in ancient human populations (SN: 9/9/00, p. 164: http://www.sciencenews.org/20000909/fob1.asp), Collinge asserts. "Selection for [the protective genes] has been widespread and began very early in the evolution of modern humans," Collinge says.
A previous study led by Collinge determined that people with one regular copy and one mutated copy of what he calls "the prion-protein gene" were protected against Creutzfeldt-Jakob disease. The scientists did not find anyone with two mutated copies; those with two regular copies were not protected. The mutation consists of a single amino acid substitution at a specific location. Other researchers studying Japanese populations found that a different mutation on the same gene had a comparably protective effect.
Collinge's team studied DNA sections containing the critical gene obtained from more than 2,000 people worldwide. All the groups examined contained a substantial proportion of people with a single copy of one of the two protective mutations. People in Japan and Taiwan exhibited the lowest population rate of the variations, 6 to 8 percent. Fore villagers had the highest rate?55 percent.
These genetic patterns indicate that "balancing selection" took place, Collinge proposes. In this rare phenomenon, also seen with malaria, individuals with different versions of the same gene receive more protection against infectious diseases than those with two copies of the common version do.
A prion disease acquired in prehistoric populations through cannibalism represents the most likely explanation of the high prevalence of people with one mutated and one regular prion protein gene, in Collinge's view.
Although the new data are suggestive of early cannibalism and kurulike diseases, they're also consistent with the presence of prion diseases that result from eating meat of nonhuman animals, comments anthropologist Henry Harpending of the University of Utah in Salt Lake City.
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References and Sources for this Article
References:
Mead, S. . . . and J. Collinge. In press. Balancing selection at the prion protein gene consistent with prehistoric kurulike epidemics. Science. Abstract available at http://dx.doi.org/10.1126/science.1083320.
Further Readings:
Bower, B. 2000. Ancient site holds cannibalism clues. Science News 158(Sept. 9):164. Available at http://www.sciencenews.org/20000909/fob1.asp.
Seppa, N. 1997. Prion proponent wins Nobel for medicine. Science News 152(Oct. 11):229.
______. 1997. Mad cow disease, human illness tied. Science News 152(Oct. 4):212. Available at http://www.sciencenews.org/sn_arc97/10_4_97/fob1.htm.
Sources:
John Collinge
Medical Research Council
Prion Unit
Department of Neurodegenerative Disease
Institute of Neurology
University College
Queen Square
London WC1N 3BG
United Kingdom
Henry Harpending
Department of Anthropology
University of Utah
Salt Lake City, UT 84112-0060
From Science News, Volume 163, No. 15, April 12, 2003, p. 229.
