A few weeks ago p-ter posted on the fact that a gene that is implicated in blondeness in humans, KITLG, has a binding partner, KIT, within a similar affect in horses. There’s a new paper out which I blog about here that shows that KITLG has a major affect on pigmentation in stickleback fish as well as humans, specifically showing a a partially dominant skin-lightening effect in African Americans in an admixture study. So like OCA2 this is now plausibly a case where selection for skin color could have driven secondary changes in phenotype (hair color). This makes more evolutionary sense since blonde hair is considered to be recessive, and so at a great selective disadvantage at low frequencies. In contrast, if skin-lightening is partially dominant it will be strongly exposed to selection (I’m skeptical of the dominance, they admit that more work needs to be done, but additivity has the same, less marked, advantage over recessivity). Note that KITLG shows up in tests of selection for East Asians too. You can find details for KITLG in this paper, Signatures of Positive Selection in Genes Associated with Human Skin Pigmentation as Revealed from Analyses of Single Nucleotide Polymorphisms, and showed up in Localizing Recent Adaptive Evolution in the Human Genome too. Note that the most recent paper, cis-Regulatory Changes in Kit Ligand Expression and Parallel Evolution of Pigmentation in Sticklebacks and Humans, is open access.