Positive selection on EDAR, why East Asians & Native Americans have thick hair

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Positive Selection in East Asians for an EDAR Allele that Enhances NF-κB Activation:

Genome-wide scans for positive selection in humans provide a promising approach to establish links between genetic variants and adaptive phenotypes. From this approach, lists of hundreds of candidate genomic regions for positive selection have been assembled. These candidate regions are expected to contain variants that contribute to adaptive phenotypes, but few of these regions have been associated with phenotypic effects. Here we present evidence that a derived nonsynonymous substitution (370A) in EDAR, a gene involved in ectodermal development, was driven to high frequency in East Asia by positive selection prior to 10,000 years ago. With an in vitro transfection assay, we demonstrate that 370A enhances NF-κB activity. Our results suggest that 370A is a positively selected functional genetic variant that underlies an adaptive human phenotype.

We’ve blogged about EDAR before; Could it be hair form?, EDAR controls hair thickness and EDAR and hair thickness. The story here is simple, before the populations ancestral to the Native Americans had left eastern Asia a mutation on the EDAR gene swept nearly to fixation among these populations. The derived SNP in particular is correlated with the thicker hair typical of East Asians and Native Americans. In other populations (Europeans, Africans, West and South Asians as well as Papuans and Melanesians) the SNP is in an ancestral state. The main twist in this study is that they used a molecular genetic technique to show that this derived state seems to upregulate the activity of NF-κB transcription factor.

For the record, I’m really skeptical that this selective sweep occurred because the human populations of late Ice Age eastern Asia developed a really strong attraction to thick luxuriant hair with full body. The paper is Open Access, read the whole thing. Since the most interesting figure is either too small or too large, I’ve resized it appropriately and placed it below the fold.


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6 Comments

  1. I tried to find in your blog articles on “thin hair”. I figured that if you are so interested in “thick hair” you would have discussed “thin hair” before. But the results returned zilch.

  2. EDAR has pathological mutants that result in thin hair. but yeah, baldy don’t do it for me….

  3. why East Asians & Native Americans have thick hair 
     
    Shucks, when I saw this I thought maybe there were some interesting findings that hinted at *why* this was selected for, but instead all I get is more data that shows: yes, sure enough it’s this gene that makes for thick hair. The paper also indicates a role in the development of teeth and sweat glands, though; if I had to guess at why this was selected for I’d lean in that direction rather than towards sexual selection based on hair. 
     
    I also saw this in the paper: 
     
    Only one chromosome from the data set carried the ancestral 370V allele and we removed it from the analysis and assumed that the 370A allele had reached fixation. 
     
    Isn’t this kind of cheating? More to the point, couldn’t they have used the frequency represented by having one ancestral allele in the data (one out of 46 is ~ 2%) and done the time regression based on that? Further, doesn’t the presence of one ancestral allele widen our Bayesian estimate of the actual frequency a fair bit, and so add even more dramatically to the uncertainty in the time estimate? In short, isn’t their estimate for the time depth questionable, perhaps even bogus, and probably too high? 
    Personally I would guess that either tooth morphology or differences in sweat gland formation (both possibly influenced by EDAR) are more likely drivers of selection than hair thickness. But I’ve always tended to think that sexual selection follows after functional selection is already well underway, and not the other way around.

  4. Could it be that there was selection for thicker hair, so that lice had a harder time clinging onto the Hair Shaft – and so was a genetic way to de-louse, which came under positive selection? 
     
    The article states: 
    In North America, black persons are less commonly affected by head louse infestation than persons from any other racial group. This is probably due in part to the use of pomades and in part because the claw size of the head louse is more adapted to the round shape of the hair shaft found in white persons and Asian persons.

  5. I think lice can evolve faster than people (at least when we’re talking about small size changes). Also, you’d want an explanation of why this anti-louse mechanism was only selected for in Asia – lice are a worldwide phenomenon AFAIK. In North America I could readily believe that the most prevalent types of lice would be adapted to the most common hair thickness(es), which is to say those of white people. But it strains belief to think that they couldn’t adapt if their host population’s hair thickness changed over a few thousand years.

  6. pconroy, your idea about the lice is interesting and well worth looking into. 
     
    bbartlog wrote: “Personally I would guess that either tooth morphology or differences in sweat gland formation (both possibly influenced by EDAR) are more likely drivers of selection than hair thickness.” 
     
    –My first thought when I read this article was to wonder if this gene could be the cause of the famous ear-wax difference between certain Asians and the rest of the world. Dry ear-wax could be adaptive to arctic conditions, and been fixed early in this poplulation.

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