A gene that causes lighter skin pigmentation in indigenous people in southern Africa has rapidly evolved in recent human history. Called SLC24A5, the gene was introduced from eastern African to southern African populations just 2,000 years ago.
Researchers say that strong positive selection caused this gene to rise in frequency among some KhoeSan populations, because the group has not experienced enough recent migration to account for the frequency of the gene (The Proceedings of the National Academy of Sciences, Dec. 10, 2018).
“[This is a] rare example of intense, ongoing adaptation in recent human history and is the first known example of adaptive gene flow at a pigmentation locus in humans,” the authors wrote in their report. The lead author, Meng Lin, is a post-doctoral researcher in genetics at the University of Southern California, according to a press release.
According to the investigators, individuals who carry two copies of the lighter pigmentation gene are 14% lighter-skinned than the population average in that region.
The gene, which is also present in people from the east Asia and eastern Africa, was probably first brought into the region by only a small number of individuals.
A shift from consuming vitamin D-rich marine animals to consuming pasture animals, or a reduction in exposure to ultra-violent rays, may have changed skin pigmentation over time, according to the investigators.
“While the biological cause of the selective event merits further investigation, we have demonstrated an unusual rapid case of selection for lighter skin pigmentation based on a recently introduced allele less that 2,000 years ago, the first case of pigmentation adaptation from migration in humans,” the paper concludes.