Rapid genetic evolution linked to lighter skin pigmentation in a southern African population

Credit: CC0 Public Domain

Populations of indigenous people in southern Africa carry a gene that causes lighter skin, and scientists have now identified the rapid evolution of this gene in recent human history.

The gene that causes lighter pigmentation, SLC24A5, was introduced from eastern African to southern African populations just 2,000 years ago. Strong positive selection caused this gene to rise in frequency among some KhoeSan populations.

UC Davis anthropologist Brenna Henn and colleagues have shown that a gene for lighter skin spread rapidly among people in southern Africa in the last 2,000 years.

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," according to the paper published online in the Proceedings of the National Academy of Sciences on Dec. 10.

The findings are based on research by multiple scientists. The primary author, Meng Lin, conducted the research as a graduate student at Stony Brook University, working with anthropologist Brenna Henn, now of the University of California, Davis, Genome Center and Department of Anthropology. Lin is now a post-doctoral researcher in genetics at the University of Southern California.

In , the researchers looked at pigmentation variation in two KhoeSan populations from South Africa by performing a genome-wide association analysis in about 450 individuals. They followed up on the top associated gene, SLC24A5, by simulating population histories with and without positive selection. The DNA and pigmentation sampling took place in the Northern Cape of South Africa in the southern Kalahari Desert and Richtersveld regions.

Gene plays a role in lighter skin pigmentation

Individuals who carry two copies of the lighter pigmentation gene are 14 percent lighter-skinned than the average, the researchers said. The gene SLC24A5 plays a key role in the genetic basis of light skin pigmentation.

While light skin is often associated with European ancestry, even in South Africa, the present-day Khoekhoe and San did not experience enough recent migration to account for the frequency of the gene. Rather, strong positive selection during the past 2,000 years was the only way to explain the current distribution. The gene, which is also present in people from the Near East and eastern Africa, was probably initially brought into the region by only a small number of individuals.

The actual source of the positive selection is not clear. The researchers theorize that a shift from consuming vitamin D-rich to consuming pasture animals, or a reduction in exposure to ultraviolent rays, might have changed skin pigmentation over time.

"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 adaptation from migration in humans," the paper concludes.

Explore further

Skin pigmentation is far more genetically complex than previously thought

More information: Meng Lin el al., "Rapid evolution of a skin-lightening allele in southern African KhoeSan," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1801948115
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Dec 10, 2018
Doubtful that Adaptation had anything to do with such changes in pigmentation. More like a group of men from the Near East with lighter complexion genes came in contact with some Khoekhoe and San women and got them pregnant. If the children of the women intermarried with each other, then the gene would have remained to be passed on in succeeding generations.
No evolution or adaptation needed.

Dec 10, 2018
That's funny, SEU. "No evolution or adaptation needed" for there to have already been lighter skinned men around.

Dec 11, 2018
No evolution or adaptation needed.

Evolution is ***very much needed*** because the change in the population allele frequency *is* precisely that process. And of course the mutations that caused the allele in the first place as well as the migration that they see are both examples of main evolutionary mechanisms:

- mutation, recombination, gene flow (migration): increase variation
- selection, drift, inbreeding: (can) decrease variation

Biology 101; read all about it in basic biology texts/classes.

I don't doubt the finding of strong positive selection if the simple population models get that is the simplest explanation.

Sure, breeding stratification *could* happen, but you need to show that, it is against the migration pattern seen above, and famously Khoekhoe and San in general do not outbreed women. And did not the paper sanity check that? I don't find the question problematic, so I am not going to do the leg work of - I have to assume - a creationist troll.

Dec 11, 2018
that's the segue for you, a bigoted fakir with his usual disregard of facts.

Now myself, being of Pure Heart & Resounding of Mind. I immediately jumped to the assumption that that the usual bores, boers & boring brits.
In their full evangelical fervor.
Had been raping the native women, children & goats at every opportunity.

Which leaves me wondering why? Out of all the biblical taboos & proscriptions. The one that pious christians cannot resist violating? Is the rule against committing bestiality!

It is their racist doctrines to claim that anyone not strong enough to fight them off? Must be of inferior breeds of subhuman or nonhuman stock.

Yet these self-appointed guardians of all that is moral?
Lack the backbone of self-discipline when it comes to mass rape & pederasty.

If the conclusions of the research claimed in this article, are confirmed correct?
Yet another boost for the scientific Theory of Evolution & Adaptive Processes in Genetics.

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