[BRIEF NOTE] The Neandertals live!

[rfmcdonald]

This GNXP link made me happy. Let's go to the Scientific American's Kate Wong.

Researchers sequencing Neandertal DNA have concluded that between 1 and 4 percent of the DNA of people today who live outside Africa came from Neandertals, the result of interbreeding between Neandertals and early modern humans.

A team of scientists led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig pieced together the first draft of the sequence—which represents about 60 percent of the entire genome—using DNA obtained from three Neandertal bones that come from Vindija cave in Croatia and are more than 38,000 years old. The researchers detail their analysis of the sequence in the May 7 Science.

The evidence that Neandertals contributed DNA to modern humans came as a shock to the investigators. “First I thought it was some kind of statistical fluke,” Pääbo remarked during a press teleconference on May 5. “We as a consortium came into this with a very, very strong bias against gene flow,” added team member David Reich of Harvard University. But when the researchers conducted additional analyses, the results all pointed to the same conclusion.

The finding contrasts sharply with Pääbo's previous work. In 1997 he and his colleagues sequenced the first Neandertal mitochrondrial DNA . Mitochondria are the cell’s energy-generating organelles, and they have their own DNA that is distinct from the much longer DNA sequence that resides in the cell’s nucleus. Their analysis revealed that Neandertals had not made any contributions to modern mitochondrial DNA. Yet because mitochondrial DNA represents only a tiny fraction of an individual’s genetic makeup, the possibility remained that Neandertal nuclear DNA might tell a different story. Still, additional genetic analyses have typically led researchers to conclude that Homo sapiens arose in Africa and replaced the archaic humans it encountered as it spread out from its birthplace without mingling with them.

But mingle they apparently did, according to the new study. When Pääbo’s team looked at patterns of nuclear genome variation in present-day humans, it identified 12 genome regions where non-Africans exhibited variants that were not seen in Africans and that were thus candidates for being derived from the Neandertals, who lived not in Africa but Eurasia. Comparing those regions with the same regions in the newly assembled Neandertal sequence, the researchers found 10 matches, meaning 10 of these 12 variants in non-Africans came from Neandertals. (Where the other two segments came from remains unknown.)

Intriguingly, the researchers failed to detect a special affinity to Europeans—a link that might have been expected given that Neandertals seem to have persisted in Europe longer than anywhere else before disappearing around 28,000 years ago. Rather the Neandertal sequence was equally close to sequences from present-day people from France, Papua New Guinea and China, even though no Neandertal specimens have turned up in the latter two parts of the world. By way of explanation, the investigators suggest that the interbreeding occurred in the Middle East between 45,00 and 80,000 years ago, before moderns fanned out to other parts of the Old World and split into different groups.

Razib Khan also links to a very extended John Hawks post that explains Pääbo's process in great detail. Neandertals went extinct, true, because their genes weren't evolutionarily adaptive, but they did leave genetic traces in the human population. That shouldn't be too surprising, since the latest genetic studies and recent anthropological surmises suggest that although more than 90% of human genes derive from ancestral populations in East Africa circa one hundred thousand years ago, a substantial percentage of genes come from other hominid populations, like the Neandertals or perhaps Homo erectus or maybe other hominid populations as yet undiscovered. There maybe be alternative models, but if the current surmises prove true the existence of fertile hybrids between Homo sapiens sapiens and the Neandertals suggest that we should be considered a single species with some variations. In some measures, Neandertals are less different from non-African humans than from any of the different regional populations of Africa.

The idea that the Neandertals left some progeny, of a sort, some genetic legacy, pleases me. Despite everything, something survived.