- Anthropology: Neanderthals and 'sapiens', a love story of 100,000 years ago
- Paleontology. 'Homo sapiens' did not cause the extinction of Neanderthals
Since the nineteenth century, the relationship between modern man - us - and Neanderthals has been the subject of all kinds of discussions and hypotheses. Only 20 years ago, the dominant idea was that we never came across this species. But, the more science advances, the clearer it is that hybridization was common. Even, as just discovered, he left his mark in Africa.
A new method to analyze and compare DNA has revealed that the African population, contrary to what was believed, retains a significant amount of Neanderthal genes , although this extinct species never inhabited that continent. In fact, and as the same research has revealed, all modern populations studied retain Neanderthal ancestry in their genome. Asians and Europeans, meanwhile, have presented very similar levels of Neanderthal genetic inheritance, superior in both cases to Africans.
"It is the first time that a true sign of Neanderthal ancestry has been detected in Africans," said Lu Chen, one of the authors of the study, conducted at Princeton University and published in the journal Cell . Previous work had estimated that in Africa there was no genetic inheritance of Homo neanderthalensis , and that this was greater in some Asian populations than in Europe.
However, a new method of analysis and comparison of genetic sequences, called IBDMix , has yielded the surprising conclusion that we are all a little Neanderthal . Scientists believe that African hybridization occurred thanks to migratory movements back and forth between continents, before the great Out of Africa movement that dispersed Homo sapiens throughout Europe, Asia and, eventually, the entire planet.
That is, the study has not only changed our perspective on the genetic inheritance of Neanderthals, but also on the movements of our ancestors at the dawn of humanity . In fact, part of the Neanderthal ancestry found in various African populations "is, in fact, due to human DNA in the Neanderthal genome from a previous cross between humans and Neanderthals," Aaron Wolf, lead author of the study since Princeton University.
"We believe that this early case of crossing involved a human group that left Africa before the main migration," Wolf added. Before the great migratory event, then, there must have been sapiens who left Africa and crossed with the Neanderthals. But most of the Neanderthal heritage we preserve today is due to another " common hybridization event that involved the ancestral population of all non-Africans, " said Joshua Akey, a professor at Princeton and also author of the study.
The results suggest that there have been continuous movements of small human groups back to Africa during the last 20,000 years. These migrations extended the Neanderthal inheritance that now, almost 40,000 after the extinction of that species, has been found in several African populations. " Hybridization between humans and nearby species was a frequent situation in our evolutionary history," Wolf said.
"I am surprised that we often think of human history in too simple terms. For example, we imagine that there was only one dispersion of modern humans from Africa 60,000 to 80,000 years ago," said Akey. "However, our results show that this story is much more interesting and that there were numerous waves of dispersal from Africa, some of which led to the genetic mix between modern and Neanderthal humans that we have observed in all living individuals today."
New statistical technique
The new statistical technique used to identify Neanderthal genes is based on the principle of "identity through offspring (IBD)," Wolf explained. "A section of DNA is identical in two individuals because those individuals once had a common ancestor," he said. The IBDMix technique takes a pair of genomes - in this case, a human and a Neanderthal one - and analyzes them for matches.
The Princeton group compared the Neanderthal genome with that of 2,504 individuals from various geographical backgrounds, which allowed us to establish that the Neanderthal ancestry of Eastern Europeans, South Asians and Asians was very similar, despite the fact that previous research had found more coincidences between East Asians and the extinct species. In the case of Africans, Neanderthal inheritance is less, but also significant, at around 0.3% of the genome .
Unlike other methods, IBDMix does not need a reference population to confirm its results. A problem with previous studies, according to Wolf and his colleagues, is that they took the African population as a reference, assuming that they had no Neanderthal ancestors.
Therefore, the new research will force to rethink several assumptions, both methodological and related to the origins of our species. "We have barely begun to explore the complex history of migrations and genetic mixtures in the African continent," Wolf concluded. "The interaction between these populations and the European ones is an additional complication that we must track."
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