It is notable that no gene shows a shared signature of selection in Europeans and Chinese, relative to Africans. These results suggest that the lighter skin pigmentation observed in non-African populations is the result of positive selection on different loci in different human populations. The identification and analysis of additional genes involved in human skin pigmentation and the functional characterization of the allelic variants at the candidate loci presented here will help clarify the nature and extent of skin pigmentation adaptation in human populations.
These results probably suggest that early Eurasians were dark, and evolved their light skin pigmentation separately, with different genes contributing to the depigmentation of Caucasoids and Mongoloids.
Human Genetics (online first)
Identifying genes underlying skin pigmentation differences among human populations
Sean Myles et al.
Skin pigmentation is a human phenotype that varies greatly among human populations and it has long been speculated that this variation is adaptive. We therefore expect the genes that contribute to these large differences in phenotype to show large allele frequency differences among populations and to possibly harbor signatures of positive selection. To identify the loci that likely contribute to among-population human skin pigmentation differences, we measured allele frequency differentiation among Europeans, Chinese and Africans for 24 human pigmentation genes from 2 publicly available, large scale SNP data sets. Several skin pigmentation genes show unusually large allele frequency differences among these populations. To determine whether these allele frequency differences might be due to selection, we employed a within-population test based on long-range haplotype structure and identified several outliers that have not been previously identified as putatively adaptive. Most notably, we identify the DCT gene as a candidate for recent positive selection in the Chinese. Moreover, our analyses suggest that it is likely that different genes are responsible for the lighter skin pigmentation found in different non-African populations.