Saturday, September 07, 2013

The Antiquity of Blonde Hair

Case reopened.

Humans today are a mix of several species from the Homo genus - at least 3 (Homo sapiens, Homo Neanderthalensis, Homo denisova) and probably more when all is said and known.

A graphic from this article [New DNA Evidence ...] shows that linkage between modern Melanesians (who frequently exhibit blonde hair) and archaic Denisovans occurred around 40,000 years ago.

This article [Blonde Melanesians ...] provides some additional interesting information on the antiquity of Oceanic blonde hair, asking the question, "is this trait an independent occurrence of de-pigmentation in Oceania, or was it due to introgression of European alleles?"

The author (Razib Khan) answers his own question:

First, one must note that this is not an isolated feature in Oceania. Rather, blondism crops up in the Solomon Islands, in New Guinea, as well as among some Australian desert groups. This in itself should make us skeptical of the model of [modern human - my addition] European admixture. Additionally, blue eyes, which exhibits a higher frequency in Europeans than blonde hair, is not similarly common in these populations.

Though some scientific studies have reported Melanesian blonde hair to be tied to a recent selected mutation in the TYRP1 pigmentation related locus found among Melanesians, it doesn't close the case that blondism in Melanesians is also linked to deep ancestry rather than solely to a population-specific mutation in the TYRP1 locus (a mutation which is not found in Europeans).

 Khan goes on to write:

But there’s a very good reason I never expected there to be recent selection driving this anyhow: Australian Aboriginals sometimes manifest blonde hair, and the best genetic data suggests separation from Melanesians of at least 10,000 years. Additionally, the Solomon Islands were not part of Sahul, so that’s a conservative estimate. We don’t know if the Aboriginals have the same TRYP1 mutation, but there’s the same tendency toward dark skin and light hair amongst them. It also seems rather suspicious to me that the highest frequency of blonde hair outside of West Eurasia is all amongst Oceanian populations, who are phylogenetically a distinct clade [as are European populations - my addition].

What I am suggesting then is that this pigmentation mutation is an old feature of the Oceanian populations, on the order of tens of thousands of years. 

... and what I am suggesting is that the "tens-of-thousands of years old feature" found amongst Oceanic groups (whatever specific mutation or mutations is are responsible for overt phenotypic expression of the trait) is indeed connected to their shared Denisovan ancestry (linking these populations around 40,000 years ago before the Melanesians and the Aboriginal Australians split genetically around 10,000 years ago).

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