Modern humans, meet the relatives: Neanderthals. It turns out, based on a new fossil analysis out Thursday, that people of European and Asian descent inherited a small amount, an average 1% to 4% of their genes, from the extinct species.
Humans and Neanderthals likely interbred 50,000 to 80,000 years ago in the Near East, concludes the international genetics team's pair of studies in the new issue of the journal Science. The research was led by German genome researcher Svante Paabo of the Max-Plank Institute for Evolutionary Anthropology. The finding splits the difference in a long-running scholarly debate over whether people are solely African in origin, or spring from "multiregional" interbreeding of early human species.
"This paper shows that the right theory is 'Mostly Out of Africa,' " says population geneticist Henry Harpending of the University of Utah in Salt Lake City. "This study is a spectacular work of (gene) sequencing technology."
For the past decade, past fossil studies of Neanderthal genes produced by the team had downplayed the odds of interbreeding, Paabo acknowledged. But the analysis of three Neanderthal-era bones allowed researchers to produce a 60% complete genetic map of Neanderthals, giving them much more statistical power to discern genetic history.
"It's a small but very real proportion of ancestry in non-Africans today," says study co-author David Reich of Harvard Medical School. The study is based on samples from three bones from Neanderthal skeletons that were 38,000 to 45,000 years old, compared with the gene maps of five modern humans from different parts of the world.
Stocky, thick-browed and heavy-boned, the Neanderthals last shared a common ancestor with the African precursors to modern humans about 500,000 years ago. The Neanderthals populated the Near East and Europe until they vanished from the fossil record about 30,000 years ago. The gene maps produced by the DNA analysis of the bones found Neanderthal genes scattered randomly among non-Africans, Paabo says, indicating they don't account for any racial differences between modern-day Africans and anyone else. Also, the study finds no sign of human genes intruding into the Neanderthal lineage.
"From the fossil record, we might have supposed that any interbreeding would have taken place about 100,000 years ago, so this is a bit unexpected," says paleontologist Ian Tattersall of the American Museum of Natural History in New York City. Prehistoric humans and Neanderthals shared roughly the same tools and lifestyle at this time, whereas by about 60,000 years ago, modern-looking humans had better tools and made decorations indicating cultures far different than Neanderthals.
The studies also revealed a few dozen genes altered in humans since they genetically diverged from Neanderthals; some related to skull and brain development. But overall, "they were not very genetically distinct from us," Paabo says.