Ancient Humans Evolved New Blood Types After Leaving Africa

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Ancient Humans Evolved New Blood Types After Leaving Africa:

Blood types-A positive, O negative, AB positive, and others-aren't just letters you need to remember when giving or receiving blood. The groups, which are based on the immune proteins in a person's red blood cells, are coded in our genes, and each evolved to carry strengths and weaknesses against particular pathogens. A study out today in Scientific Reports reveals the blood types of early modern humans who lived throughout Europe and Asia between 46,000 and 16,500 years ago, as well as those of our close cousins, the Neanderthals. The results shed light on their comings, goings, and commingling, and could help researchers better understand blood type interactions today.

"[Blood types] have been a really strong target of positive selection throughout our history," says Joshua Akey, a population geneticist at Princeton University who wasn't involved with the work, and they reflect the diseases ancient people encountered. Likely as a result of such ancient exposures, people with type O blood are more likely to have severe cholera infections, but are more resistant to severe malaria. And although humans have 47 different blood groups, which can play a vital role in our immune defenses, researchers are not yet sure how all of them originated.

But little is known about the origin of these blood groups or exactly how they've changed over human evolution. To learn more, Stephane Mazieres, a genetic anthropologist at Aix-Marseille University, turned to previously sequenced genomes from 22 Homo sapiens individuals who lived from 46,000 to 16,500 years ago, 14 Neanderthals who lived roughly between 120,000 and 40,000 years ago, and a single individual from about 98,000 years ago thought to be descended from both Neanderthals and another close cousin, the Denisovans. The ancient DNA from these people came from sites scattered throughout Eurasia, from modern-day Germany to Siberia and China.

In these genes, the team zeroed in on markers for 10 blood groups that are medically relevant today because they can cause fatal complications during blood transfusions if they aren't compatible with the recipient's type. They found that blood groups in Neanderthals remained mostly unchanged during their last 80,000 years of existence, even though this group mingled with other hominins before going extinct roughly 40,000 years ago. This makes sense, Mazieres says, because Neanderthals overall had very little genetic diversity across their relatively small population, and having limited variety in their blood groups reflects that.

H. sapiens's blood types told a different story. As our species migrated out of Africa between 70,000 and 45,000 years ago and expanded into Eurasia, new genetic variants determining blood groups emerged and entrenched themselves in these roving populations.

"It's fascinating that every single ancient human they looked at had these unique variants," says Fernando Villanea, a population geneticist at the University of Colorado Boulder who was not involved in the new study. It was "very unexpected" that they would have evolved in such a short time, he says.

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