NEW YORK — A new genomic analysis of the blood groups of Neanderthals and Denisovans provides a glimpse into their evolutionary history and suggests they likely arose in Africa.
Blood group was one of the first phenotypic markers used by anthropologists to study the origins and movements of human populations, Silvana Condemi, a scientist at the French National Center for Scientific Research and first author of the new study, said in an email, but advances in genome sequencing have overshadowed its use.
In their study, published in PLOS One on Wednesday, Condemi and her colleagues instead used recently generated genome sequences for three Neanderthals and one Denisovan to determine their blood types and examine their evolutionary history. They found that the ancient hominins harbored a range of ABO blood types and patterns of alleles that suggested they have an African origin. Further, the Neanderthal individuals harbored an Rh allele only seen in one Australian Aboriginal individual and one Papuan individual so far, hinting at a possible ancient admixture event. Additionally, the analysis underscored the low genetic diversity of Neanderthals and pointed to a potentially higher risk of hemolytic conditions affecting fetuses and newborns that could have reduced their reproductive success and contributed to their disappearance.
"Far from being obsolete, this [work] shows the importance of the study of blood systems to understand the evolutionary history of humans, the diffusion in Eurasia of our species, as well as its encounters with other humans (Neanderthals and Denisovans)," Condemi said.
She and her colleagues analyzed high-quality genomes from one Denisovan and three Neanderthal individuals who lived between 40,000 years and 100,000 years ago across Eurasia. They focused on seven blood group systems — not only the ABO and Rh systems but also Kell, Duffy, and others — and 11 associated genes. For each ancient hominin, the researchers determined the genotypes and likely phenotypes for these blood group systems.
Under the ABO system, two Neanderthals had an A1 phenotype and another had a B phenotype, while the Denisovan had an O phenotype. The researchers noted Neanderthals were previously all thought to be blood type O under the ABO system, but instead they found here that the ancient hominins had the most common ABO types found among modern humans.
Meanwhile, Neanderthals and Denisovans harbored certain combinations of Kell, Duffy, Kidd, and MNS blood type system alleles that have only been found among modern African populations. This, the researchers said, supports the idea that the ancient hominins also originated in Africa.
The researchers additionally found a partial RHD allele that was present among the three Neanderthal individuals but not in the Denisovan. This allele, they noted, had previously only been identified in 2019 in an individual from the First Nation of Australia, and they additionally found it in an indigenous Papuan individual. This suggests that admixture may have occurred between Neanderthals and modern humans before the latter reached Southeast Asia.
The analysis also highlighted Neanderthals' demographic vulnerability, the researchers said. In addition to their low genetic diversity, the analysis found that all three Neanderthal individuals had partial Rh antigens. This can contribute to hemolytic disease of the fetus and newborn and could have affected the reproductive success of Neanderthals.
Condemi said they plan to expand their analysis to additional archaic human genomes, especially from Denisovans, as well as from early Homo sapiens individuals.