A recent genetic study sheds new light on the history of Neanderthals and Sapiens. While our modern ancestors have been able to adapt quickly to new environments in Eurasia, the Neanderthals seem to have been handicapped by their blood biology. According to this research, published on January 23 in the journal Scientific Reports, the incompatibility between the blood groups of the two species would have contributed to the extinction of the Neanderthals.
Understand blood groups: more than a question of compatibility
THE blood groups humans are defined by specific molecules, called antigens, which are on the surface of red blood cells. These antigens, like those of the ABO system (groups A, B, AB and O), determine the way in which the immune system recognizes blood cells. The HR factor, another antigen, adds an additional distinction by classifying blood groups like RH-Postifs or RH-Negatives.
Although crucial for the proper functioning of the body, these characteristics can also cause serious incompatibilities. When a person receives an incompatible blood transfusion, the immune system attacks foreign red blood cells, which leads to potentially fatal complications.
Likewise, incompatibility can occur during pregnancy. For example, if an RH-Negative woman carries an RH-Post-time fetus, her immune system can consider the red blood cells as a threat. It then produces antibodies which attack these cells, which causes a Hemolytic disease of the newborn (MHNN). This disease can have serious consequences for the child: jaundice, severe anemia, brain damage, even death. Today, this problem is notified thanks to the prenatal administration of immunoglobulins which block the production of antibodies in the mother. However, 100,000 years ago, such intervention was impossible.
A fascinating discovery on the blood of Neanderthals
As part of a study, researchers from the University of Aix-Marseille studied the genome of several ancient individuals, including Neanderthals, Denisovians and Homo sapiens (DNA already sequenced by other teams). Their objective: to explore the variations of blood groups and better understand the evolution of red blood cells.
-Their analysis revealed a surprising characteristic: Neanderthals had a very rare HR factor type (parent of certain HRs today present among populations of sub -Saharan Africa), distinct from that of the denomievians and the first Homo sapiens. This last code for a partial rhesus, that is to say positive, but incomplete.
Researchers explain that Neanderthals probably have this very rare and distinct type of HR factor due to their long isolation and their low genetic diversity. Unlike Homo Sapiens, who have migrated and interacted with various groups in different environments, Neanderthals have lived in relatively small and isolated populations in Eurasia for tens of thousands of years. This isolation would have limited genetic exchanges with other human groups and thus reduces the opportunities for diversifying their genetic heritage, including that of the antigens of red blood cells.
What consequences?
According to Stéphane Mazières, geneticist of the populations and co-author of the study, this HR variant was incompatible with those of other human groups. This incompatibility would have been particularly problematic in cases of hybridization between Neanderthals and Homo Sapiens. In the case of pregnancies involving a woman with this rare HR and a complete positive HR fetus or partial HR, but not the same, so the child was likely to develop a Hemolytic disease of the newborn (MHNN) possibly fatal. In the case of pregnancies involving the opposite, either complete HR woman (sapiens, Denisova) and partial HR fetus (Neanderthal, like the father), then there was no risk.
In short, if the causes of the extinction of Neanderthals remain complex and multidimensional, this study adds an important piece to the puzzle. She suggests that biological factors, such as blood incompatibilities, have also been able to play a role just as crucial as climate change, diseases or competition with Homo sapiens.
