1Ecology and Evolution, Stony Brook University, 2Analytic and Translational Genetics Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston
April 21, 2017 , Studio 7
Skin pigmentation is under strong directional selection for reduced melanin density in northern European and Asian populations. Conversely, dark pigmentation is thought to be under stabilizing selection in equatorial populations exposed to intense ultraviolet radiation. We high-throughput sequenced pigmentation genes in over 400 individuals from South Africa and demonstrate that a canonical skin pigmentation gene, SLC24A5, experienced recent adaptive evolution in the KhoeSan populations of far southern Africa. The functionally caustive allele lightens basal skin pigmentation by 4 melanin units, explaining 11.9% variance in pigmentation in these populations. Haplotype analysis and demographic models indicate that the allele was introduced into the KhoeSan only within the past 3,000 years likely by eastern African pastoralists. The most common haplotype is shared among the KhoeSan, eastern Africans and Europeans but has risen to a frequency of 25%, far greater than expected given initial gene flow. The SLC24A5 locus is a rare example of strong, ongoing adaptation in very recent human history.