February 1, 2014

Studies find Neanderthal genes in modern humans

WASHINGTON — Neanderthal genes lurk among us. Small traces of Neanderthal DNA have been confirmed in the areas of the genome that affect skin and hair of modern humans, according to two new studies that also give clues as to which Neanderthal traits may have been helpful - or harmful - to the survival of our species.

The studies, published online Wednesday in the journals Nature and Science, came to similar conclusions despite using vastly different methods of genomic analysis.

For East Asian and European populations, genes that provide the physical characteristics of skin and hair have a high incidence of Neanderthal DNA - possibly lending toughness and insulation to weather the cold as early man emerged from Africa, the studies conclude. Neanderthals were thought to have already been adapted to a chillier, more northern environment.

Perhaps most notably, Neanderthal DNA was not found in genes that influence testicles, according to the Nature study, hinting that when the Neanderthal ventured outside his own species for sex, the introduction of his DNA may have reduced male fertility in early humans.

"There's strong evidence that when the two met and mixed, they were at the edge of biological compatibility," said Nature study author and Harvard University geneticist David Reich. "The people who eventually survived and thrived had quite a bit of hurdles to overcome."

This is consistent with what is seen in nature: When two species mate that are sufficiently far away biologically, the resulting hybrids tend to have lowered fertility. Early humans and Neanderthals interbred about 40,000 to 80,000 years ago around the Middle East, during man's migration out of Africa.

And the last Neanderthals died off some 30,000 years ago.

Reich's team used an ancient genome his lab had sequenced last year - as high-quality as any modern DNA data set - from a 130,000-year-old female Neanderthal's toe bone found in a Siberian cave. They compared her data with 1,004 genomes of present-day humans, including those of sub-Saharan Africans. The Science study, led by University of Washington geneticist Joshua Akey, only used East Asian and European sequences, because indigenous Africans possess little or no traces of Neanderthal.

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