Humanity’s “Out of Africa” moment encoded in our DNA

Spanning hundreds of miles across Iran’s west, with its northern edges extending into Iraqi Kurdistan, the Zagros Mountains are popular with explorers and provide sustenance for the many villages, farms, and pastoralists that call the region home.

This mountain range is also known as an ancient Silk Road crossroads of civilizations, hosting armies and traders from the East and West long before the modern era.

Earlier still, Iraq’s Shanidar Cave was once home to Neanderthals.

Neanderthal remains were recovered in the cave back in the 1950s. There is strong evidence that these Neanderthals and Denisovans, another species of extinct archaic human, crossed paths with the earliest Homo sapiens in these ranges for thousands of years. Scientists also say that early Homo sapiens bred with these archaic, extinct offshoots of modern humanity.

Now, researchers in France say they’ve uncovered evidence that the first Homo sapiens to venture out of Africa evolved a special trait shortly after leaving the continent, traits that allowed them to outlive other hominin species and conquer Eurasia and the world.

“Neandertal inhabited the Near East also, so the first encounter of Sapiens with Neanderthal would have been this region,” Stéphane Mazières, a researcher at Aix Marseille University in France and the lead author of the new study, told Public Parks.

Human ancestors comingling

Traces of Neanderthals, Denisovans, and ancient Homo sapiens have been uncovered in the Zagros Mountains. A Neanderthal skull and partial skeleton were unearthed in Shanidar Cave. Not much was known of how these species intermingled until modern DNA analysis techniques provided long-sought-after clues.

Thanks to genetic tracing, we now know that traces of Neanderthal DNA survive today in our bloodlines, meaning our kind interbred with theirs millennia ago.

This new study from France claims to have uncovered—genetically—the moment that a branch of Homo sapiens became distinct from both Neanderthals and the original humans who remained in Africa, possibly gaining traits in their blood that permitted them to spread across all of Eurasia.

“Homo sapiens may have undergone adaptive genetic changes in their blood groups after leaving Africa,” the researchers wrote.

The study points to evidence that early Homo sapiens bred with Neanderthals and Denisovans in the Zagros Mountains and beyond for at least 100,000 years.

Even as this was occurring, the Homo sapiens populating these regions retained a particular change in their blood type—Rh alleles—that could’ve paved the way for Homo sapiens to expand their range throughout Eurasia and ultimately to Oceania and North America.

In other words, Mazières and his team believe they’ve uncovered, through genetic discovery, that part of the world where the human population first to conquer Eurasia became genetically distinct from the original humans who remained in sub-Saharan Africa.

“The Near East—more at the West of the Persian Plateau, present-day Jordan, Israel, Syria—could be an ideal candidate place because numerous Neanderthal were already living there,” he said.

Separated by blood

The differentiation is found in blood groups.

By tracing genetic histories, the scientists say Neanderthals’ blood type alleles—particular DNA markers in blood—resemble groups of modern humans found predominantly in sub-Saharan Africa. Having emerged from Africa, human groups known to have populated Eurasia should have these alleles in their blood, as well.

But they don’t.

Rather, the differentiated Rh alleles are commonly found in humans that populated Eurasia, and these alleles “are crucial blood types in transfusion and pregnancy monitoring,” they wrote.

“Understanding changes to blood groups resulting from these interactions could help in determining human migration patterns and where potentially advantageous genetic changes developed,” the authors argue.

The research team’s findings have been published in the journal Scientific Reports.

Mazières et al. theorize that ancient humans developed this dominant blood trait over a period of at least 15,000 years.

A transformation out of Africa

In correspondence with Public Parks, Mazières confirmed that the pattern of humanity’s emergence from Africa looked something like the following.

Homo sapiens are believed to have left Africa about 60,000 to 70,000 years ago, and possibly earlier. The “remaining in Africa” population of Homo sapiens retained greater genetic diversity as the migrating population drifted away.

These “Out of Africa” Homo sapiens encountered populations of Neanderthals and Denisovans already living in the Levant and Zagros area.

By this time, the Out of Africa population of Homo sapiens likely had already developed the different blood group genes, evolving to have a distinctive blood group apart from sub-Saharan Africa Homo sapiens.

We know this, Mazières argues, because this blood group type (Rh) is present in modern humans from Eurasia today, but not in sub-Saharan Africa, meaning the trait survived despite the ancient interbreeding of Out of Africa Homo sapiens with Neanderthals and Denisovans, and despite the greater genetic diversity in sub-Saharan Africa Homo sapiens.

This evolutionary change likely afforded the Out of Africa Homo sapiens traits that enabled their survival in Eurasia, he says.

“Neanderthal inhabited the Near East also,” Mazières added, “so the first encounter of Sapiens with Neanderthal would have been this region.”

His research team also theorizes that this change in blood type may have endowed these early humans with traits beneficial for evolution and survival outside of Africa.

“Presently, some blood groups are effectively advantageous against infectious diseases such as malaria, cholera, and Covid-19,” he explained.

Another clue is the fact that early genetic diversity in sub-Saharan Africa is higher.

This is due to the “founder effect” whereby an original population develops more complex genetics over time, while a branch or offshoot population that migrates away in smaller numbers takes more time to develop in population size and genetic diversity.

Though evidence suggests that Neanderthals retained blood type traits similar to humans in sub-Saharan Africa, “Homo sapiens who had just left Africa underwent an allele diversification before expanding throughout Eurasia, which explains why some red cell blood group antigens are presently present outside of Africa,” Mazières et al. explain in their newly published paper.