Could it be hair form?
In Genome-wide detection and characterization of positive selection in human populations there’s an interesting part which intrigues me:
The EDAR polymorphism is notable because it is highly differentiated between the Asian and other continental populations…and also within Asian populations (in the top 1% of SNPs differentiated between the Japanese and Chinese HapMap samples). Genotyping of the EDAR polymorphism in the CEPH…global diversity panel…shows that it is at high but varying frequency throughout Asia and the Americas (for example, 100% in Pima Indians and in parts of China, and 73% in Japan)…Studying populations like the Japanese, in which the allele is still segregating, may provide clues to its biological significance.EDAR has a central role in generation of the primary hair follicle
pattern….
What’s going on? My blind and fact-free guess is this polymorphism has something to do with hair form. Eye-balling the map I see that Cambodians are balanced for ancestral and derived, and they’re the Southeast Asian population which is “Mongoloid” that stereotypically has the curliest hair. As for the ~73% value in Japan, that makes sense if you accept the finding that Japanese are hybrid population between Yayoi rice farmers from the East Asian mainland and Jomon natives to a ratio of 3:1, with the latter exhibiting the ancestral allele and the former the derived. The Jomon were probably a collection of people of whom the Ainu of Hokkaido are/were the last distinct remnants in the historical period. The Ainu of course have less stereotypically East Asian features despite their genetic relatedness to other groups in Northeast Asia. One of their characteristics is a tendency toward wavy hair.
(note that this doesn’t mean that I think there was selection for thick very straight hair. I assume it is likely a byproduct effect)
Labels: Population genetics
I assume it is likely a byproduct effect
Social conformity? Which would be weird, given that domesticated animals tend to develop wavier or curlier hair… meh, human exceptionalism! We need some good personality info on how rascally the Japanese are compared to the Chinese.
Actually, depending on which Amerindian groups those are, maybe I’ll take that back…
could be anything. read the paper closer, it isn’t just hair. it’s a major developmental pathway.
I’m not sure how selective it would be, but hair texture/curliness matters a lot for head lice. Current human phenotypes mean lice have to ‘pick’ African or non-African hair and are bad at infesting the other kind.
Fsev,
Interesting that the derived kind is found in East Asians and even more so in Native Americans – could this be that this was in response to different species of lice, or to having a relatively hairless body??
This article on Human Lice Species, says that:
They confirmed that P. humanus comprises two lineages?one contains both head and body forms and has worldwide distribution; the other contains only the head louse and is restricted to the New World?but discovered that P. humanus originated long before its H. sapiens host.
The above article suggests that Modern Humans and Archaics (Asian Homo Erectus) may have been in close contact, and a lice species jumped from one to the other. Another interpretation would be that Native Americans and less so East Asians are directly related to some Archaic human sub-species (like Neanderthal?).
Who knows??
Actually, Cambodians (Khmers) are just as admixed, if not more so, as the Japanese. The fact is in the numbers of mtDNA studies. For example, if neighboring Thai mtDNA says anything, Khmers are heavily “aboriginal negrito” on their maternal side. Thailand used to be part of the Khmer territory before Tais took over and assimilated the people, so the Thai numbers should be roughly equivalent to Khmer make-up.
owtopic=1584.
The relevant studies are linked in this post, http://z6.invisionfree.com/man/index.php?sh