Human population genetics and origins
Africa is thought to be the ancestral homeland of all modern human populations. It is also a region of tremendous cultural, linguistic, climatic, and genetic diversity. Despite the important role that African populations have played in human history, they remain one of the most under-represented groups in human genomics studies. A comprehensive knowledge of patterns of variation in African genomes is critical for a deeper understanding of human population history in Africa and the genetic basis of adaptation during human evolutionary history. Identification of functionally important genetic variants that impact human adaptation remains a challenge, particularly for complex traits influenced by multiple genes. Skin pigmentation is a classic example of a complex adaptive trait in humans. However, little is known about the genetic basis of skin pigmentation, particularly in Africa. To alleviate this disparity, we have measured skin pigmentation in a broad range of ethnically diverse Africans and have looked for associations with genomic variants. We observe a wide range of skin pigmentation in Africans and we identify novel variants associated with skin color including a previously uncharacterized gene that plays a critical role in production of pigment in melanocytes. These genes show signatures of natural selection and in many cases, the ancestral variant is associated with light pigmentation. Further, most variants originated before the origin of modern humans in Africa. These data shed light on the genetic basis of skin pigmentation in humans and exemplify how natural selection has shaped the human genome.