Blood that wiped out Neanderthals: how genetic incompatibility shaped human evolution.

When early modern humans left Africa, their red blood cells may have rapidly evolved, helping them to survive in new environments. However, this same adaptation might have contributed to the extinction of Neanderthals, as suggested by the authors of a recent study, writes Live Science.

Blood groups, defined by antigens on red blood cells, play a crucial role in immune system compatibility. While many are familiar with the ABO blood groups and the Rh factor that determines whether a blood type is positive or negative, red blood cells are far more complex and contain hundreds of other antigens.

These variations are inherited, prompting a team from the University of Aix-Marseille in France to examine ancient genomes to trace the evolutionary history of Neanderthals, Denisovans, and modern humans. The researchers sequenced the genomes of individuals living between 120,000 and 20,000 years ago and discovered a rare blood group in Neanderthals that could have been potentially fatal for their newborns.

According to Stéphane Mazières, the lead author and population geneticist, Neanderthals had a rare Rh antigen that was incompatible with early Homo sapiens and Denisovans. This incompatibility likely led to hemolytic disease of the newborn during interbreeding, causing severe anemia or even death in Neanderthal offspring. While modern medicine can treat Rh incompatibility, such conditions would have been incurable 100,000 years ago, possibly accelerating the extinction of Neanderthals.

The study also indicated that modern variants of the human Rh gene originated from early Homo sapiens, who likely developed them shortly after migrating out of Africa. This adaptation may have occurred on the Persian Plateau, where environmental pressures and population growth contributed to rapid changes in red blood cell diversity. In contrast, Neanderthals and Denisovans exhibited limited diversity, probably due to isolation and inbreeding, which may have further contributed to their extinction.

This research provides insight into how ancient human adaptations shaped survival and interspecies interactions, revealing complex connections between genetics and history. Understanding these evolutionary changes not only deepens our knowledge of early humans but also highlights the vulnerability of populations in the face of genetic and ecological challenges.

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