An adaptive variant of the human Ectodysplasin receptor, EDARV370A, is one of the strongest candidates of recent positive selection from genome-wide scans. We have modeled EDAR370A in mice and characterized its phenotype and evolutionary origins in humans. Our computational analysis suggests the allele arose in central China approximately 30,000 years ago. Although EDAR370A has been associated with increased scalp hair thickness and changed tooth morphology in humans, its direct biological significance and potential adaptive role remain unclear. We generated a knockin mouse model and find that, as in humans, hair thickness is increased in EDAR370A mice. We identify new biological targets affected by the mutation, including mammary and eccrine glands. Building on these results, we find that EDAR370A is associated with an increased number of active eccrine glands in the Han Chinese. This interdisciplinary approach yields unique insight into the generation of adaptive variation among modern humans.
The mutation was found in a gene for ectodysplasin receptor, or EDAR,
part of a signaling pathway known to play a key role in the development
of hair, sweat glands and other skin features. While human populations
in Africa and Europe had one, ancestral, version of the gene, most East
Asians had a derived variant, EDARV370A, which studies had linked to
thicker scalp hair and an altered tooth shape in humans.
The ectodysplasin pathway is highly conserved across vertebrates —
the same genes do the same thing in humans and mice and zebrafish. For
that reason, and because its effects on skin, hair and scales can be
observed directly, it is widely studied.
This evolutionary conservation led Yana Kamberov, one of two first
authors on the paper, to reason that EDARV370A would exert similar
biological effects in an animal model as in humans. The HMS research
fellow in genetics developed a mouse model with the exact mutation of
EDARV370A — a difference of one DNA letter from the original, or
wild-type, population. That mouse manifested thicker hair, more densely
branched mammary glands and an increased number of eccrine, or sweat,
Update (Feb 20): Razib Khan also finds the suggested “selection sweep” dubious, and his discussion of this paper is very interesting to read.
An interesting detail that I could not gather clearly from the abstract is that the allele causes (at least in mice) smaller breasts and not just denser mammal glands.
But surely the most interesting item is this map of the frequencies of the EDARV370A allele through the World, being very much and quite strictly limited to the peoples displaying what is classically described as the Mongoloid phenotype:
An intriguing issue is also the lack of it in Europe, even among peoples of well-known Siberian/East Asian low-level admixture (Northern Russians). I’m tentatively imagining some sort of “racist selection” against the trait among those peoples, as it expresses an exotic, possibly not favored (to put it mildly), very apparent phenotype. Food for thought.