Phylogeny of human beta-globin haplotypes and its implications for recent human evolution

Abstract

The evolutionary histories and relationships among African, Eurasian, and Pacific Island populations are investigated by using observations on five polymorphic restriction sites in the beta-globin gene cluster. We present new data on 222 chromosomes from a global sample and combine these with previously published observations on 591 chromosomes. It is shown that the data are rich in rare haplotypes and that rare variants are not helpful for standard methods of population structure analysis. Consequently, a new approach is developed. We first consider the phylogeny of beta-globin haplotypes. The roles of mutation, gene conversion, and recombination in the generation of haplotype diversity are specifically focused upon. The relationships among human populations are then inferred from the phylogenetic relationships among the haplotypes, their presence or absence, and frequencies within populations. Questions regarding whether or not a phyletic process can account for relationships among the major geographical populations and whether or not an extant human population exhibits the qualities that would be expected of an ancestral group are addressed. The results of this analysis support an African origin for modern Homo sapiens and a phyletic structuring of the major geographical regions. However, it is shown that divergence times for the various populations cannot be determined from these data.