Colo. - Researchers examining understudied populations in
Africa have found that skin pigmentation is far more varied and complex than
previously understood. And that complexity increases nearer the equator.
studies have focused on more homogeneous European and Eurasian populations and
concluded that pigmentation was governed by just a handful of genes,” said
study co-author Christopher Gignoux, PhD, MS, associate professor at the
Colorado Center for Personalized Medicine at the University of Colorado Anschutz Medical Campus.
“But in this study we looked at pigmentation among African populations and
found a striking variability that has been underappreciated.”
study, published in the November edition of the journal Cell, is the
culmination of a decade’s worth of research involving scientists from CU
Anschutz, the State University of New York at Stony Brook, Stanford University,
Stellenbosch University, and the Broad Institute of MIT and Harvard.
researchers studied two populations of the KhoeSan people, the Khomani San and
the Nama. Both live in South Africa and have much lighter skin than other
Africans who live closer to the equator.
conducted interviews, recorded height, age and gender and used a reflectometer
to measure skin color of about 400 people. They discovered that skin
pigmentation is highly heritable but that doesn’t explain its variance and
complexity. Instead of a few genes controlling the process as many thought,
they found far more genes involved, each one contributing something different.
And many of the genes have yet to be discovered. Only about 10 percent of that
previously discovered variation can be linked to genes impacting pigmentation
in the KhoeSan.
finding showed that the closer a population moves to the equator, the more
genes come into play that can influence variability.
skin pigmentation in the KhoeSan appears to be due to a combination of many
small-effect mutations as well as some large-effect variants,” said the study’s
senior author Brenna Henn, assistant professor of ecology and evolution at SUNY
of those mutations, Henn said, may have arisen in southern Africa more than
100,000 years ago and were selected for in Europeans after they left Africa for
higher latitudes where pigment lightens to absorb more sunlight which produces
vitamin D and folate protection.
argue that the distributions of skin pigmentation globally suggest different
forces of selection operating at various latitudes,” Henn said.
order to understand baseline pigmentation, she said, it’s important to study a
large set of genetically diverse populations that have historically been
exposed to different levels of ultraviolet radiation.
agreed saying earlier notions of skin pigmentation being relatively simple
underestimated the genetics involved.
higher latitudes there is far less difference in skin pigmentation and that’s
where most of the earlier research was done,” he said. “But there is more
pigmentation variation on the African continent than any other place on earth
and its needs further study.”