In a new study, researchers have discovered that Neanderthals and humans interbred tens of thousands of years earlier than previously thought. The discovery was made when early modern human DNA was found in a Neanderthal genome.
Since geneticists sequenced the first Neanderthal genome back in 2010, researchers have been discovering just how close we are related to our ancient, extinct cousins.
Researchers from the Cold Spring Harbor Laboratory (CSHL) made the discovery after examining the remains of a Neanderthal woman who lived about 100,000 years ago in the Altai Mountains, Siberia. The study shows that one or more of her relatives were, in fact, human.
Professor Adam Siepel, a co-team leader and Cold Spring Harbor Laboratory (CSHL) quantitative biologist, said in a statement:
“One very interesting thing about our finding is that it shows a signal of breeding in the ‘opposite’ direction from that already known. That is, we show human DNA in a Neanderthal genome, rather than Neanderthal DNA in human genomes.”
The paper provides the first ever genetic evidence of the scenario where early modern humans left the African continent,and mixed with archaic (now-extinct) members of the human family prior to the migration “out of Africa” of the ancestors of present-day non-Africans, less than 65,000 years ago, CSHL wrote in an statement.
Professor Siepel, said:
“It’s been known for several years, following the first sequencing of the Neanderthal genome in 2010, that Neanderthals and humans must have interbred.
“But the data so far refers to an event dating to around 47,000-65,000 years ago, around the time that human populations emigrated from Africa. The event we found appears considerably older than that event.”
According to CSHL, this finding, the result of several kinds of advanced computer modeling algorithms comparing complete genomes of hundreds of contemporary humans with complete and partial genomes of four archaic humans, has implications for our knowledge of human migration patterns.
Watch this video from ColdSpringHarborLab about their discovery:
The authors explain why there are parts of Neanderthal DNA still remaining in human genomes:
“People living today who are of European, Eurasian, and Asian descent have well-identified Neanderthal-derived segments in their genome. These fragments are traces of interbreeding that followed the “out of Africa” human migration dating to about 60,000 years ago. They imply that children born of Neanderthal-modern human pairings outside of Africa were raised among the modern humans and ultimately bred with other humans.
“Contemporary Africans, however, do not have detectable traces of Neanderthal DNA in their genomes. This indicates that whatever sexual contact occurred between modern humans and Neanderthals occurred among humans who left the African continent.”
Co-author, Ilan Gronau, explains:
“Ancestors of present-day African populations likely didn’t have the opportunity to interbreed with Neanderthals, who lived largely outside of Africa.”
The evidence of “gene flow” from descendants of modern humans into the Neanderthal genome applies to one specific Neanderthal called the “Altai Neanderthal,” and came from a tiny toe bone fragment.
The modern human sequences in the Altai Neanderthal appear to derive from a group of modern human ancestors from Africa that separated early from other humans, about the time present-day African populations diverged from one another, around 200,000 years ago.
Thus, there must have been a long lag between the time when this group branched off the modern human family tree, roughly 200,000 years ago, and the time they left their genetic mark in the Altai Neanderthal, about 100,000 years ago, before being lost to extinction themselves, CSHL wrote.
The studies analyze more than 500 genomes of contemporary Africans. Martin Kuhlwilm from Max Plank Institute for Evolutionary Anthropology who was involved in the study, said:
“I was looking to see if I could find genomic regions where the Altai Neanderthal has sequences resembling those we see in humans.
“We know that contemporary non-Africans have traces of Neanderthal in them, so they were not useful in this search. Instead, we used the genomes of contemporary individuals from five populations across Africa to identify mutations which most of them have in common.”
This was the data that provided evidence of “regions in the Altai Neanderthal genome that carry mutations observed in the Africans — but not in the Denisovan” or in Neanderthals found in European caves, CSHL explained.
“This is consistent with the scenario of gene flow from a population closely related to modern humans into the Altai Neanderthal. After ruling out contamination of DNA samples and other possible sources of error, we are not able to explain these observations in any other way,” Siepel said.
The scientists detailed their findings in a paper titled: “Ancient gene flow from early modern humans into Eastern Neanderthals,” which was published in the journal, Nature.
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