A new study led by by scientists from the Cold Spring Harbor Laboratory and various international researchers utilized numerous DNA analysis techniques in order to reveal that an interbreeding event between Neanderthals and modern humans took place approximately 100,000 years ago, tens of thousands of years earlier than previously believed.
"It's been known for several years, following the first sequencing of the Neanderthal genome in 2010, that Neanderthals and humans must have interbred," Adam Siepel, coauthor of the study, said in a press release. "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."
"One very interesting thing about our finding is that it shows a signal of breeding in the 'opposite' direction from that already known," Siepel added. "That is, we show human DNA in a Neanderthal genome, rather than Neanderthal DNA in human genomes."
The team used various advanced computer modeling algorithms to compare the complete genomes of hundreds of modern humans with the complete and partial genomes of hundreds of archaic humans.
The results showed that modern humans who are European, Eurasian and Asian have identifiable Neanderthal-derived segments in their genetics, which are remnants of the interbreeding that took place during the human migration out of Africa approximately 60,000 years ago. However, contemporary Africans do not contain traces of Neanderthal DNA in their genetics, a sign that sexual contact between modern humans and Neanderthals took place between only those who left the African continent.
"Ancestors of present-day African populations likely didn't have the opportunity to interbreed with Neanderthals, who lived largely outside of Africa," said coauthor Ilan Gronau.
The team also examined the genetics of another ancient human relative, a Denisovan individual. Like Neanderthals, Denisovans are a member of the human lineage that eventually became extinct. The remains examined were obtained from the same cave as those of another Neanderthal examined in the study. However, the results showed that the individual did not have traces of modern human DNA. Does this mean that modern humans never mated with Denisovans?
According to Siepel, it doesn't - he claims that the evidence "probably comes from an interbreeding event that occurred after this Neanderthal lineage diverged from its archaic cousins, a little more than 100,000 years ago."
The findings were published in the Feb. 17 issue of Nature.
