Tag: Blonde Melanesians

Why Melanesians are blonde resolved?

By Razib Khan | August 31, 2011 12:08 pm

Sort of and possible. I’ve been talking about this for years, and Greg Cochran points me to an abstract at the human genetics conference referenced earlier. Novel coding variation at TYRP1 explains a large proportion of variance in the hair colour of Solomon Islanders:

The Solomon archipelago comprises over 1,000 islands located east of Papua New Guinea and has a population noted for wide variation in hair pigmentation. 1200 samples were collected from 16 centres and hair colour measured in donors by spectrophotometer. Analysis of 589,241 single nucleotide polymorphisms across a subset of 42 dark haired and 43 blond haired individuals revealed a signal for pigmentation driven by 27 markers on 9p23 at the TYRP1 gene (rs13289810…). There were no systematic differences in ancestry between dark and blond haired participants indicating that this variation is unlikely to be due to recent introgression from other populations. Sequencing of TRYP1 showed complete conservation of this locus bar nucleotide 5,888(NG_011750), which was homozygous C in dark haired individuals and T in blonds. The resulting CGC->TGC missense mutation changes the 93 amino acid in exon 2 from an Arginine to a Cystine. Genotyping of TYRP1(93C/T) in all samples and analysis showed that in a recessive model including sex, age and local geography, there was a -1.67(-1.76, -1.50) standard deviation difference in hair colour by genotype groups (p=3.5e-106) equating to ~40% variance in this trait. Genotyping in the Human Gene Diversity Panel showed TYRP1(93C/T) to be essentially private to the Solomon Islanders…In humans, complete loss of function for Tyrp1 is known to cause rufous albinism. This is one of the only examples of a genomewide association study implicating causal variation directly, of a common local variant of functional effect being absent in other human populations and is one of the largest phenotypic effects attributable to a common polymorphism. Reasons for the maintenance of this variation are unclear, however this finding prompts the notion that we may find other large (disease causing) effect variants that are population specific and that our results are a call to arms to expand medical genomics to underrepresented populations.

Australian Aboriginals are not present in the HGDP panel, so there is no clarity on blondism in those populations, or amongst other indigenous groups in Southeast Asia and Oceania. If these are deep ancient variants then this may span all these populations. If not, then you see independent occurrences of a phenotype which is only present in Europeans and European-derived/admixed populations elsewhere. Why? One hypothesis I’ve thrown out is that it is possible that the expansive of agriculture populations erased a great deal of past human phenotypic diversity, due to the demographic growth of small initial founding groups ~5-10,000 years ago.

The question mark in the title by the way is that just because we characterize the genomic architecture of a trait, we don’t understand why it is distributed in the way it is. Perhaps small populations resulted in more genetic drift in Oceania than elsewhere? Or there is selection on the TYRP1 locus, and this trait is a side effect?

CATEGORIZED UNDER: Human Genetics, Human Genomics

Blondes of the 'black islands'

By Razib Khan | August 18, 2010 4:07 am

Populations_first_wawe_migrRecently I was looking for images of the alpine biomes of the New Guinea highlands* and stumbled onto some intriguing, though not entirely surprising, set of photographs of individuals from Papua New Guinea. They were noteworthy because they manifested the conventional Melanesian physical type, but their hair had a blonde cast to it. For example, here is a charming blonde boy. The photographer has several other striking portraits of Melanesians with lighter hair at his website. In regards to the peculiar hair color of these people he says: “When you ask the people why there are so many blonde people on the islands, they answer 3 things: they have white ancestors, they receive too much sun, or they do not eat enough vitamins! – Langania village, New Ireland, Papua New Guinea.” There is more discussion in the comments about this issue, some claiming that likely it is the sea water and sun which is producing bleaching naturally. If you look around you will see references to bleaching of hair among some of these people as a cultural trait, though the references tend not to be concrete (many clearly assume they’re bleaching their hair, rather than reporting bleaching). The blonde being at the tips from what I can tell in some cases I certainly don’t reject the explanation that bleaching is a cultural practice among these peoples, albeit for children and women only.

But the peculiar hair color of these populations is noted in the scientific literature as if it is a biological characteristic of these groups, not a cultural artifact. From Molecular genetic evidence for the human settlement of the Pacifc: analysis of mitochondrial DNA, Y chromosome and HLA markers: “The Tolais of New Britain are phenotypically ‘Melanesian’, with fairly dark skin and frizzy hair, some-times almost blonde as in some highland Papuan groups.” Enter Tolai ‘New Britain’ into Google Images and the first few pages have several instances of blonde children, including this cute triplet.

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CATEGORIZED UNDER: Genetics, Genomics

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