A recent study reveals that a rapid evolution in red blood cells among modern humans may have contributed to the extinction of Neanderthals. Researchers sequenced genomes from individuals who lived between 120,000 and 20,000 years ago, discovering that Neanderthals possessed a rare blood group potentially fatal to their newborns. This study was published on January 23 in the journal Scientific Reports.
Blood groups are defined by proteins and sugars, known as antigens, on red blood cells. The ABO blood typing system categorizes blood into groups A, B, AB, and O. Antigens are recognized by the immune system, and mismatches can trigger immune responses. The Rh factor further classifies blood types as positive or negative, crucial for blood transfusions.
Researchers from Aix-Marseille University in France examined ancient genomes to explore the evolutionary history of Neanderthals, Denisovans, and modern humans. Lead author Stéphane Mazières noted that Neanderthals had an Rh blood group rare in contemporary humans. This Rh variant, a type of RhD antigen, was incompatible with those found in Denisovans or early Homo sapiens.
Mazières stated, “For any case of inbreeding of a Neanderthal female with a Homo sapiens or Denisova male, there is a high risk of hemolytic disease of the newborn.” This condition can result in jaundice, severe anemia, brain damage, and death, potentially contributing to Neanderthal population decline.
Modern humans have varied Rh protein presence on red blood cells, with complications arising in Rh-negative individuals carrying Rh-positive fetuses. Rh incompatibility can lead to the immune system attacking fetal red blood cells, causing hemolytic disease. Current treatments involve administering immunoglobulin to prevent antibody production, a solution unavailable 100,000 years ago.
The researchers found that Rh gene variants in many present-day individuals originated from early Homo sapiens, likely evolving soon after leaving Africa, possibly on the Persian Plateau. In contrast, Neanderthal Rh variants remained largely unchanged for 80,000 years.
Mazières suggested that the isolation of Neanderthals may explain the lack of evolution in their red blood cells. The rapid diversification of early human red blood cells over at least 15,000 years raises questions about demographic expansion and adaptation to new environments in Eurasia.
This research aligns with archaeological and genetic studies, indicating that new genetic lineages and stone tool industries emerged in the Persian Plateau between 70,000 and 45,000 years ago. The limited diversity in Neanderthal and Denisovan red blood cells during the same period may suggest inbreeding and declining populations, ultimately leading to their extinction.