The Zagros Mountains would have provided the perfect conditions for the co-existence of the Neanderthals and the Sapiens.
We may have finally found the answer to one of the most complex mysteries in our evolutionary history. Although the interbreeding of Neanderthals and Sapiens has been documented, the timing and geography of their encounter has remained a mystery due to a lack of fossils and DNA.
Today, however, researchers from the University of Cologne (Germany) have identified a contact zone, namely the Zagros Mountains (between Iran and Iraq), which could have allowed Neanderthals and Sapiens to interbreed and change the fate of our species.
Their study was published in the journal Scientific Reports.
Neanderthals and Sapiens
That between Neanderthals and Sapiens is a never-ending story.
That their paths crossed at some point in history is now beyond dispute. In fact, we know for certain that the coexistence of the two species in northern Europe goes back at least 45,000 years, and that the genome of modern Eurasian populations contains an average of 2% DNA from the Neanderthal population.
In particular, these genes can affect several aspects of our health. As reported in the scientific literature, they can predispose carriers to a severe form of Covid-19, where they develop an excessive immune response and are less able to defend themselves against infection. But they can also affect the tendency to get fat, the development of diseases such as schizophrenia, and the colour of hair and skin.
Meeting in the Zagros Mountains
By combining genetic, archaeological, topographical and ecological data, researchers at the German university concluded that Neanderthals and Sapiens interbred in the Zagros Mountains. This area includes one of the best-known Neanderthal sites, Shanidar Cave, where the remains of ten individuals have been discovered.
“We believe that the Zagros Mountains acted as a corridor… facilitating the northward dispersal of modern humans and the southward dispersal of Neanderthals,” the article states.
The Zagros Mountains, the researchers explain, may have connected the Palaearctic and Afrotropical realms. A place, in other words, where the environmental conditions best suited to both modern humans and our now extinct cousins overlap.
Migration waves
Until recently, it was thought that our Sapiens ancestors left Africa in a single wave of migration about 50,000 years ago, meeting Neanderthals in Asia and Europe.
But a recent study published in Science suggests that things may have been different. In fact, the authors of the study, a group of geneticists from Princeton University and Southeast University in Nanjing, believe that Sapiens migrated out of Africa in several waves, at least three, and that the first interbreeding with Neanderthals occurred at least 250,000 years ago.
Not one, but three intersections
“This is the first time,” said Liming Li, a Princeton researcher and co-author of the paper, “that geneticists have identified multiple waves of mixing between ‘modern’ humans and Neanderthals.
To find out, the researchers compared the three most complete Neanderthal genomes currently available, from samples found in the Vindija cave in Croatia (50-65 thousand years old) and the Chagyrkaya and Denisova caves in Russia (50-80 thousand years old), with the genomes of around 2,000 modern humans.
The comparison was carried out using a machine-learning algorithm called IBDmix, which can reconstruct and map the flow of genes from one species to another: in this way, they identified three separate ‘waves’ of interbreeding dating back 250-200 thousand years, 120 thousand years and 100 thousand years respectively.
This discovery suggests that Sapiens left the African continent on several occasions. “The fact that we were able to include the Neanderthal genomic components in our study,” commented Joshua Akey, another author of the paper, “means that it is now possible to see ‘dispersals’ that we could not see before.”
Time and resources
The time frame identified by the German researchers is between 120 and 80 thousand years ago, which coincides with the second wave of interbreeding, some of which is still written into our genes.
“Archaeological and genetic evidence suggests that Sapiens entered Southwest Asia at this time,” the researchers explain. Moreover, the Zagros region, with its high biodiversity, had enough resources for both species to coexist, and the diversity of environments allowed them to find refuges when climatic conditions became harsh and extreme.
And it may even have been these climatic changes that brought the two species closer together, increasing their interactions and enabling interbreeding and genetic exchange.
Sources and Data
- Neanderthal e Sapiens, uno studio ha identificato il luogo in cui si sono incrociati | Wired Italia
- Sapiens e Neanderthal si sono accoppiati (almeno) in tre momenti diversi | Wired Italia
- Recurrent gene flow between Neanderthals and modern humans over the past 200,000 years | Science
- Reconstructing contact and a potential interbreeding geographical zone between Neanderthals and anatomically modern humans | Scientific Reports (nature.com)
