Neandertal legacy written in Europeans’ fat metabolism

Fat metabolism genes inherited from Neandertals may have helped Stone Age humans survive in Europe around the time when cave lions and saber-toothed cats ranged the continent.

Remnants of these genetic gifts pop up in the genomes of modern-day Europeans and appear to tweak fat levels in their brains, researchers report April 1 in Nature Communications.

The findings are the latest in a string of studies trying to suss out the role Neandertal ancestry might have played in human evolution (SN: 3/8/14, p. 12).

Each newly discovered Neandertal detail — about their hair, skin, pigmentation and now fat metabolism — reshapes scientists’ view of the ancient hominids, says paleoanthropologist John Hawks of the University of Wisconsin–Madison, who was not involved with the new work.

People used to think of humans and Neandertals as distinct groups, he says. “The reality is that they contributed to our population and they gave us things that had value.”

Hundreds of thousands of years ago, Neandertals lived in Europe, the Middle East and Asia. After humans migrated out of Africa some 70,000 years ago, they met up and interbred with Neandertals. Today, evidence of this interbreeding peppers the genomes of these humans’ descendants — about 2 percent of non-African genomes comes from Neandertals.

That’s about as much DNA as people inherit from a great-great-great-great-grandparent, says evolutionary biologist Michael Lachmann of Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

“It’s like you have a Neandertal in your family tree.”

To find out whether interbreeding with Neandertals helped humans, Lachmann and colleagues compared Neandertal genomes that had been sequenced (SN: 3/14/09, p. 5) with genomes from 11 modern human populations. The researchers looked for collections of genes with unusually high or low levels of Neandertal sequences.

Neandertal DNA is typically sprinkled evenly throughout non-Africans’ genomes, Lachmann says. But in Europeans, genes involved in fat synthesis held more than three times as many Neandertal sequences as did other genome regions. And genetic signals hinted that this DNA might have spread rapidly through human populations.

Next the team examined whether the genetic remnants of Neandertals tinkered with fat metabolism in today’s humans. Compared with people from other parts of the world, Europeans have different concentrations of fats in the brain — the first time scientists have reported a difference in brain fat composition among human populations.

“There must be some purpose” for the genetic changes in fat metabolism, says study coauthor Philipp Khaitovich, an evolutionary biologist at the Chinese Academy of Sciences and Max Planck Society Partner Institute for Computational Biologyin Shanghai. “But we still have no idea, no idea at all.”

One possibility lies in how the brain works. Fat helps messages zip between neurons, but researchers don’t know whether the change in Europeans boosts brainpower, or whether a Neandertal-like fat metabolism helped ancient humans stay warm in cool climates. Or the genetic changes could have been adaptive for an entirely different reason that researchers haven’t dreamed up.

Scientists are still in the early stages of figuring out what humans’ Neandertal lineage says about the past, says Joshua Akey, a genome scientist at the University of Washington in Seattle.

Though researchers can pick out Neandertal contributions to humans’ genomes, the new findings underscore the idea that Neandertals and humans weren’t all that different.