A new study published in Scientific Reports finds that incompatibility between the blood groups of Neanderthals and modern humans may have contributed to the extinction of the Neanderthals.
Researchers from the University of Aix-Marseille studied the genomes of several ancient individuals—Neanderthals, Denisovans, and Homo sapiens. The study reveals that Neanderthals possessed a very rare type of Rh factor, distinct from that of Denisovans and early Homo sapiens, which could have been fatal to their newborns. Stéphane Mazières, a population geneticist and co-author of the study, stated that if Neanderthal women mated with Homo sapiens or Denisovan men, there was a high risk of newborns having neonatal hemolytic disease, which can have severe consequences, including jaundice, severe anemia, brain damage, or even death.
"In pregnancies involving a Rh-negative woman carrying a Rh-positive fetus, the woman's immune system may consider the fetus's red blood cells a threat, leading to the production of antibodies that attack the fetus's red blood cells, causing potentially fatal hemolytic disease of the newborn (HDN)," Mazières explained, according to SciencePost. "This could have contributed to the extinction of the Neanderthal population," he added.
Human blood groups are characterized by specific molecules called antigens found on the surface of red blood cells. Antigens, such as those of the ABO system (groups A, B, AB, and O), determine how the immune system recognizes blood cells. The Rh factor is another antigen that classifies blood groups as Rh-positive or Rh-negative. Neanderthals likely had a rare and distinct Rh factor due to their long isolation and low genetic diversity, coding for a partial Rh-positive but incomplete status. This Rh variant was incompatible with those of other human groups, particularly in cases of hybridization between Neanderthals and Homo sapiens.
While modern humans developed diverse blood types, Neanderthals' blood types remained largely the same due to their isolated lifestyles and declining populations, which limited genetic exchanges. In contrast, Homo sapiens had more diverse blood types, which may have given them an immune system advantage in adapting to new environments.
In modern medicine, this condition can be prevented with immunoglobulin treatment, but such treatments were not possible 100,000 years ago. The researchers suggest that Rh incompatibility could have contributed to the demise of the Neanderthal population.
Blood group characteristics, although crucial for the proper functioning of the body, can cause severe incompatibilities. When a person receives a transfusion of incompatible blood, the immune system attacks the foreign red blood cells, leading to potentially fatal complications. Incompatibility can also occur during pregnancy.
Variations in red blood cells are passed down over generations. The rapid evolution of red blood cells in early humans remains unexplained, but geographical expansion may be a contributing factor.
The causes of the extinction of Neanderthals remain complex and multidimensional. The study suggests that biological factors, such as blood incompatibilities, may have played a role as crucial as climate changes, diseases, or competition with Homo sapiens.
The article was written with the assistance of a news analysis system.