The anatomically modern humans who populate the planet today underwent changes in their blood groups after leaving Africa, between 70,000 and 45,000 years ago, and before they spread through Eurasia. These adaptive changes caused the appearance of new Rh alleles (RHD and RHCE) that still persist today and are crucial in blood transfusion and pregnancy control.
Stéphane Mazières and his colleagues at the University of Marseille in France studied genetic data from 22 Homo sapiens and 14 Neanderthals from Eurasia who lived between 120,000 and 20,000 years ago. They intended to evaluate whether the blood group diversity of Neanderthals was shared with the Sapiens populations of the Upper Paleolithic between 40,000 and 10,000 years ago. The reason is that both species interbred and had children repeatedly on the Mediterranean coast of Asia and the Zagros Mountains (present-day Iran and Iraq) since 100,000 years ago. For this reason, all but Africans carry a Neanderthal imprint in our DNA.
As explained in the magazine ‘Scientific Reports’, Genetic analysis revealed that although Neanderthals had ancestral alleles similar to those found in current peoples of sub-Saharan Africa and a rare ‘rhesus’ (protein in red blood cells) found in Oceania, the first sapiens of Eurasia had developed new Rh alleles that are not present in Neanderthals, so the authors suggest that they may have differentiated in sapiens after leaving Africa. The study also identifies three alleles absent in current humans, which could belong to a lineage of sapiens whose ancestry did not contribute to current Eurasian populations.
“The RH is made up of 8 main haplotypes, or 8 main forms of the RH genes: one ancestral, found in sub-Saharan populations, from which the other seven were derived. We knew, and confirmed with the present study, that Neanderthals carried this RH profile ancestral. We discovered that the first sapiens of Eurasia carried one of the seven derived forms. And currently, this form of RH is exclusive to non-African populations, reaching the. 40% in Eurasia This implies two things about the arrival of the Homo sapiens and the current distribution of the RH system: it would have appeared somewhere between Africa and Eurasia and we can date it to about 60,000 to 45,000 years (the age of the departure from Africa and the samples), and the distribution of the RH in current Eurasia originates on that exit from Africa. Older samples are needed to infer the age of the other forms of RH,” explains Stephane Mazieres, principal investigator of the study.
The authors believe that the sapiens population that arrived on the Persian plateau remained there for at least 15,000 years, long enough to develop Rh alleles. These alleles may have provided an evolutionary advantage to sapiens populations that were exposed to different selective pressures than populations that remained in Africa.
“The fate of a mutation depends on two factors: genetic drift over generations, which is random, and natural selection, the impact of the environment, such as altitude or pathogens, on genetics. But some blood groups confer a selective advantage over infectious diseases such as cholera, malaria, one of the gastroenteritis viruses and, as we have seen recently, Covid-19,” says Mazieres. “Rh is not the best candidate to demonstrate natural selection, but probably the blood groups found in early sapiens could have been advantageous. However, it is too early to say which pathogen or pathogens were involved. So I would say that these Changes in Rh occurred first by chance, and then were maintained in the Homo sapiens by a mixture of chance and positive selection,” he concludes.
From a biomedical point of view, adds the researcher, “these changes have provided human beings with more blood groups that intervene in mother-fetus incompatibilities or hemolytic disease of the newborn. This occurs when the fetus has a blood type different from that of the mother, so she can become immunized and attack the red blood cells of her fetus, which could be lethal for him.
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