Blood ties: ABO is a trans-species polymorphism in primates

TL;DR

This study demonstrates that the ABO blood group polymorphism is a trans-species polymorphism maintained by balancing selection across primate species for tens of millions of years, challenging the idea of convergent evolution.

Contribution

It provides evidence that ABO polymorphism is an ancient, shared genetic variation among primates, not a result of convergent evolution, highlighting a rare example outside the MHC.

Findings

ABO alleles are shared among primate species due to common ancestry.

Genetic data contradicts the convergent evolution hypothesis.

ABO polymorphism has been maintained by balancing selection for millions of years.

Abstract

The ABO histo-blood group, the critical determinant of transfusion incompatibility, was the first genetic polymorphism discovered in humans. Remarkably, ABO antigens are also polymorphic in many other primates, with the same two amino acid changes responsible for A and B specificity in all species sequenced to date. Whether this recurrence of A and B antigens is the result of an ancient polymorphism maintained across species or due to numerous, more recent instances of convergent evolution has been debated for decades, with a current consensus in support of convergent evolution. We show instead that genetic variation data in humans and gibbons as well as in Old World Monkeys are inconsistent with a model of convergent evolution and support the hypothesis of an ancient, multi-allelic polymorphism of which some alleles are shared by descent among species. These results demonstrate that the ABO polymorphism is a trans-species polymorphism among distantly related species and has remained under balancing selection for tens of millions of years, to date, the only such example in Hominoids and Old World Monkeys outside of the Major Histocompatibility Complex.