Humans probably bred with Neanderthals more than thousands of years earlier than previously thought

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Back in 2010, genome sequencing of Neanderthals had already established that there were occurrences of interbreeding between the Neanderthals and humans. In terms of date, such interbreeding scenarios were believed to have occurred around 47,000-65,000 years ago, when the human population moved out of Africa. But a new research (supported by DNA analysis) alludes to the probability that such interbreeding scenarios between Neanderthals and humans occurred much earlier, around 100,000 years ago. Simply put, this is the very first time that scientists have come across a credible genetic scope that might prove that early modern humans actually migrated out of Africa before what the conventional ‘out of Africa’ theory suggests. In other words, a group of humans possibly already traveled to other lands beyond Africa prior to the ancestors of present-day non-Africans.

This DNA analysis and groundbreaking research was done by the collaborative effort of scientists from institutions like Cold Spring Harbor Laboratory (CSHL), Max Plank Institute for Evolutionary Anthropology, Herzliya Interdisciplinary Center and Cornell University. Now we call the research ‘groundbreaking’ as it establishes a reverse pattern of breeding in humanity’s prehistory. As Professor Adam Siepel, a co-team leader and quantitative biologist at the CSHL, said –

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.

Now in terms of well documented assessments, present-day non-Africans tend to have detectable traces of Neanderthal-derived ‘bits’ in their genome. On the other hand, contemporary native Africans do not have such traces of Neanderthal genome. This suggests that the group that migrated during the ‘out of Africa’ event (60,000 years ago) bred with archaic (now-extinct) members of the human family, like the Neanderthals. The offspring produced from such unions were raised among the early modern humans, and they in turn bred with other humans, thus resulting in the transmission of the neanderthal genome traces. And given the geographical domains of contemporary neanderthals (who were based outside of Africa), the native African ancestors didn’t get the opportunity to breed with these archaic members.

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© Ilan Gronau

As for this research scope, the reverse pattern of ‘gene flow’ (from humans into neanderthal genome) was identified by the analysis of the remains of one particular neanderthal called the ‘Altai Neanderthal’. Discovered a few years ago inside a cave in southwestern Siberia (by the Russia-Mongolia border), this archaic specimen was found to have human DNA. Simply put, this surely alludes to the possibility that some modern human ancestors moved out of Africa long before the ‘out of Africa’ migration event. Such a scenario can be established by the dating process that more-or-less places the age of the Altai Neanderthal at around 100,000 years, from its extant tiny toe bone fragment.

Interestingly, the researchers have also sequenced two other neanderthal specimens, one from Croatia and the other of Spain. Surprisingly, their genome didn’t contain any traceable human DNA. To that end, the scientists have hypothesized that there was a divergence in the Neanderthal line more than 100,000 years ago, with one group moving away from their ‘European’ brethren – and the Altai Neanderthal belonged to this ‘segregated’ group.

Beyond the assessment of three neanderthal specimens, the researchers also conducted analysis of over 500 genomes of contemporary Africans. As Martin Kuhlwilm, a member of the Max Plank Institute for Evolutionary Anthropology, 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.

Siepel also reaffirmed –

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.

Source: CSHL

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