Some micropopulations have developed their own, unique, blood signatures (Bombay group is a good example here, they lack the H antigen that makes them universal

Some micropopulations have developed their own, unique, blood signatures (Bombay group is a good example here, they lack the H antigen that makes them universal donors but Bombay only acceptors). Blood types in general are super complex combinatorially. The concept of hybrid vigor (Expressing two different alleles expressed may yield a competitive advantage over expressing a single allele twice) has always interested me in regards to blood, though I haven't gone digging for a basis for that being a driving force.