Researchers have new evidence that the ABO blood groups come from a trans-species polymorphism among distantly related species that has persisted over millions of years. ABO antigens are polymorphic in humans as well as several other primates, and this recurrence had previously been understood as a result of more recent convergent evolution. Led by Drs. Laure Ségurel and Emma E. Thompson of the University of Chicago, the research group assessed genetic variation data in humans and 40 non-human species, including gibbons and distantly related Old World monkeys. Phylogenetic analysis demonstrated that the ABO polymorphism was evident across Old World monkeys, Humanoids, and New World monkeys. Researchers also modeled the expected length of a genetic sequence carrying a signal of a trans-species polymorphism, and subsequently constructed trees of ABO haplotypes for the regions around focal sites. They found that these trees clustered by type rather than species, suggesting that the A and B allelic classes stemmed from a most recent ancestor, and had been maintained across species. Furthermore, pairwise synonymous diversity between ABO allelic classes was compared to divergence within these classes. Findings were consistent with a theory of a trans-species polymorphism, but inconsistent with the theory of more recent convergent evolution. The selection mechanism responsible for maintaining the ABO polymorphism across species remains unknown.
1. Segurel L, Thompson EE, Flutre T, Lovstad J, Venkat A, Margulis SW, Moyse J, Ross S, Gamble K, Sella G, Ober C, Przeworski M. The ABO blood group is a trans-species polymorphism in primates. Proc Natl Acad Sci U S A 2012.