What Neanderthal Genes Can Tell Us About Human Migration

Provided that you’re of European, Asian, or Native American ancestry, than between 3 and 4% of your DNA is, in fact, Neanderthal- our ancient, long extinct cousins that haven’t walked the earth for 40,000 years. While this may be shocking to some readers, for scientists it’s a fact that has been known for years. According to the generally accepted theory, Homo sapiens and Homo neanderthales interbred around 55,000-60,000 years ago, probably somewhere in the Middle East after Homo sapiens emerged from Africa. This, incidentally, is why few Africans or those of African descent possess Neanderthal DNA themselves.

Yet even though most people today carry some Neanderthal in their genes, scientists believe that interbreeding was relatively rare between our species and our close cousins– else we would possess much more Neanderthal DNA than we already do. Interestingly enough, even though there is evidence of our species and Neanderthals coexisting for thousands of years together in Europe, the fact that Europeans possess no more Neanderthal DNA than Asians or Native Americans means that what interbreeding that did happen must have occurred almost exclusively in the Middle East.

This poses a perplexing problem for evolutionary biologists. If European Homo sapiens and Neanderthals really did live together in Europe, then why are Europeans not more, well, “Neanderthal-y” than Asians or Native Americans? Luckily for scientists, two discoveries made in the past few months may shed some light on this discrepancy, but as is often the case with science, these findings seem to create just as many new questions as they answer.

Humans first interbred with Neanderthals in the Middle East around 55,000 years ago Credit: Wikimedia Commons

Humans are thought to have first interbred with Neanderthals in the Middle East around 55,000 years ago
Credit: Wikimedia Commons

Oase Man

The first is the “Oase Man”, named after the Pestera cu Oase cave in Romania where he was found. This particular individual lived between 42,000 and 37,000 years ago, and, curiously, possessed jaw features similar to that of Neanderthals. Upon closer inspection, scientists discovered that between 6% and 9% of the Oase Man’s DNA was, in fact, Neanderthal, nearly three times that whic

A reconstruction of the unique jawbone of the "Oase Man" Credit: Svante Pääbo, Max Planck Institute for Evolutionary Anthropology

A reconstruction of the unique jawbone of the “Oase Man”
Credit: Svante Pääbo, Max Planck Institute for Evolutionary Anthropology

h is found in Europeans today. For the Oase Man to have so much Neanderthal DNA, he must have had a Neanderthal ancestor that lived less than 200 years before his birth–in effect, a Neanderthal great-great grandfather (or grandmother). This creates two problems for scientists: first, the interbreeding that led to the Oase Man must have occurred in Europe, not in the Middle East as current theories assume. And second, interbreeding must have occurred some 10,000 years after it should have for Europeans to have the amount of Neanderthal DNA that they have today.

To match the existence of the Oase Man with current Neanderthal DNA amounts in Europeans, scientists were forced to come up with a rather unconventional, yet also incredibly interesting, solution. They theorized that not one, but two interbreeding events must have occurred, one between Middle Eastern Homo sapiens and Neanderthals and one between European Homo sapiens and Neanderthals.

Most interestingly, this means that the Europeans of the Oase Man’s time are not the Europeans of today. Modern Europeans must instead have come into Europe sometime after the Oase Man’s birth, probably from the Middle East, and from there drove the existing Homo sapiens population into oblivion. This makes the Oase Man’s more “Neanderthal-y” Humans just as must a relic of the past as the Neanderthals themselves- a footnote of our evolutionary history, a victim of a more advanced and competitive invading population, unknown until our findings of the Oase Man’s bones in a Romanian cave.

If the Oase Man showed that Humans and Neanderthals mated long after previously thought, then the bones of a Neanderthal woman found in Siberia serve to push the limits back from where we originally believed. Whereas Neanderthal DNA is found in most humans, Homo sapiens DNA has been absent when analyzing the genomes of Neanderthal remains.

The Siberian woman is the first time human DNA has been found in a Neanderthal- between 1 and 7 percent of her genes in fact belongs to our own species. This in and of itself is notable insofar as it helps plug the holes in theories surrounding Human-Neanderthal interbreeding, and proves that the offspring of these unions were integrated into both species, not just Homo sapiens.

Human DNA was found in the toebone of an ancient Neanderthal Woman Photo Credit: Bence Viola

Human DNA was found in the toe bone of a Neanderthal Woman
Photo Credit: Bence Viola

Yet what’s more interesting is that, through analyzing the Siberian woman’s genome, scientists were able to estimate the timing of the interbreeding event between her species and ours: 100,000 years ago, which is 50,000 years before current theories believed interbreeding to have occurred- and before humans were ever supposed to emerge from Africa.

As Neanderthals never lived in Africa, this means that they must have mated with a separate population of Homo sapiens that emerged from Africa some 50,000 years before our own ancestors encountered the Neanderthals in the Middle East 50,000 years ago . The question, of course, is what happened to this population of humans. Were they outcompeted by the already-native Neanderthals, as Humans would later on do to the Neanderthals themselves? Or did later populations of Homo sapiens drive out this first wave of out-of-Africa humans, as likely happened with the European humans of the Oase Man?

So what do these two stories tell us? For one, Humans and Neanderthals have been interbreeding for much longer than the relatively brief window previously believed by scientists. Second, there seem to have been many separate waves of human migration, some of which survived and eventually led to our own genetic makeup, and others- such as the Europeans of the Oase Man or the Humans that left Africa and interbred with Neanderthals 100,000 years ago- that eventually died out, their genetic line extinct in the modern day.

 

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Devin Windelspecht – Devin is a sophomore at Northeastern University in Boston MA where he majors in international relations.  Devin is responsible for background work on many of the articles on the site, as well as some science writing.

 

One Response
  1. Torbjörn Larsson April 30, 2016 Reply

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