Kevin Webb / NHM Image Resources / The Natural History Museum, London
Reconstitution of a homo sapiens (left) and Neanderthal (right)
It wasn’t just a hitch here or there. Introgression was a geographically wide phenomenon, which covered almost the entire area occupied by Neanderthals. Iberian Peninsula is one of two exceptions.
Interbreeding between Homo sapiens and Neanderthals may have occurred over a much wider area than up until now if: in much of Eurasia and not just a limited area in the Middle East, traditionally seen as the main place of sexual contact between the two populations.
The new study in bioRxiv has not yet been peer-reviewed, but it contradicts the most repeated hypothesis so far. Today, Practically all non-African populations have traces of this encounter evolutionary: on average, about 2% of the genome of people outside of Africa contains Neanderthal DNA. Although this genetic inheritance is well known, a fundamental question remained open: where it happenedspecifically, the mixture between the two lineages during the Pleistocene.
The authors of this recent study analyzed 4,147 ancient human genetic samples, collected from 1,200 sites across Eurasia, aged between 44,000 and 6,000 years. Assuming that the first Homo sapiens from Africa arrived in Eurasia through the Levanteresearchers looked for patterns in the distribution of Neanderthal genes in human populations, observing how this genetic “signature” behaves as one moves away from that starting point.
The result dictated that, instead of decreasing, the introgression (the incorporation of Neanderthal genetic material into Homo sapiens populations) increases the greater the distance to the Levanteither east (towards Asia) or west (towards Europe). In the proposed model, the so-called “hybridization zone” extends almost 4,000 kilometers in various directions, even reaching regions as far north as the Baltic Sea.
This points to a scenario in which the contacts were not a localized event, but rather a geographically wide phenomenonwhich covered almost the entire area occupied by Neanderthals.
As exceptions identified include the region of the Altai Mountains, in Siberia, and the Iberian Peninsula, where the data does not indicate the same pattern, according to .
The team also interprets this distribution as compatible with a single continuous “pulse” of mixing, associated with the expansion of Homo sapiens out of Africa around 60 thousand years ago. But despite the territorial range, individual mating episodes would have been rare, which would help explain the relatively low proportion of Neanderthal inheritance in modern humans.
The study does not precisely establish the exact period of interbreeding, but refers to recent work that points to a beginning around 50 thousand years agopossibly lasting up to seven millennia.
