Case closed: blonde Melanesians understood

By Razib Khan | May 3, 2012 11:21 pm

As a small child perusing old physical anthropology books I would occasionally stumble upon images of people of Oceanian stock with light hair color. I would wonder: is this a biological or cultural feature? In other words, were people bleaching their hair? If it was biological, was it heritable, or was it simply malnutrition? Another aspect of the phenotype was also straightforward: it did not seem that light hair color resulted in any concomitant lightening of the skin. Granting that this was a heritable biological trait, the questions then were simple: was this trait an independent occurrence of de-pigmentation in Oceania, or was it due to introgression of European alleles?

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 European admixture. Additionally, blue eyes, which exhibits a higher frequency in Europeans than blonde hair, is not similarly common in these populations. But all this speculation is now a historical curiosity. The results are widely known from conference presentations that have been reported, but finally the paper is out in Science which solves the “riddle” of hair color in Oceania at the level of genetic causation.

Melanesian Blond Hair Is Caused by an Amino Acid Change in TYRP1:

Naturally blond hair is rare in humans and found almost exclusively in Europe and Oceania. Here, we identify an arginine-to-cysteine change at a highly conserved residue in tyrosinase-related protein 1 (TYRP1) as a major determinant of blond hair in Solomon Islanders. This missense mutation is predicted to affect catalytic activity of TYRP1 and causes blond hair through a recessive mode of inheritance. The mutation is at a frequency of 26% in the Solomon Islands, is absent outside of Oceania, represents a strong common genetic effect on a complex human phenotype, and highlights the importance of examining genetic associations worldwide.

The study was a classic cases vs. controls GWAS. They looked at variants in a lot of people with the trait, vs. those without the trait. Additionally, if you check the supplements and read the text it’s obvious there is no population straification. That is, having blonde hair is not correlated with a different ancestry in these Melanesian populations. Rather, this is a relatively robust recessively expressed trait that seems to have been segregating within these groups before contact. Those individuals who are homozygotes tend to have blond hair, while those who are not tend not to have blonde hair. TYRP1 is a pigmentation related locus, so it isn’t surprising that the mutation was around that region of the genome. The key though is to note that the specific mutation is not found in Europeans. Rather, it is limited to Oceanians. The extremely close correspondence between the genotype and the trait, and the lack of similarity in the variants between Europeans and Oceanians, ends debate on questions of the heritability and possible exotic origin of the trait in Oceanians. Now it is known, and the debate shall end.

So how did the Oceanians come to have such a high frequency of this trait? Here’s a comment from one of the preeminent biological anthropologists of Melanesia:

The mutation, which has no obvious advantages, likely arose by chance in one individual and drifted to a high frequency in the Solomon Islands because the original population was small, says Jonathan Friedlaender, an anthropologist emeritus at Temple University in Philadelphia, Pennsylvania, who was not involved in the study. “This whole area seems to have been populated by very small groups of people making it across these stepping-stone islands, so you do have very dramatic effects in fluctuations of gene frequency.”

It is absolutely correct that Oceanian populations exhibit a lot of evidence of small effective population, and so are subject to random genetic drift. In this model the frequency of ~0.25 for the allele which results in bondlism in the homozygote in the Solomon islands is high as it is due to a drift event up in frequency from an initial variant mutation. But there are reasons I am skeptical of this. The first is a somewhat technical one: if the high frequency in the Solomons is due to rapid rise in frequency due to large generation-to-generation fluctuations, you’d expect to see some linkage disequilibrium in the region of TYRP1. That’s because presumably the blonde allele comes from a common ancestor, which just happened to be over-sampled in a high drift regime. Even if it wasn’t a selective sweep, flanking SNPs would still be transmitted at high frequency with the causal variant through drift. If the drift event occurred in the past, the allele should be fixed, or, it should be extinct. If you imagine that it was fixed in some populations, and then admixture resulted in the allele segregation, then there should be LD around the SNP too.

It is noted in the text that the authors did not find evidenc of high LD in their tests for natural selection, XP-EHH or iHS. These tests are cued to pick up relatively recent selective events, on the order of ~10,000 years or so. They’re geared toward detection of correlations of variation across regions of the genome generated by positive selection (though as I suggest above, they can also yield false positives due to stochastic events, especially iHS). Additionally, using Fst, a between population genetic variation measure, the authors note that the SNP in question has a high Fst when comparing Solomon Islanders with non-Oceanians, but nearby SNPs to it do not.

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.

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. That is why there isn’t LD around this region; any LD which existed was long ago eliminated by recombination. But why is it still around at minor allele level frequencies? When all other explanations are found wanting, you go where you have to, so therefore I suggest some form of balancing selection. One could posit overdominance on a trait other than pigmentation, with the hair color being simply a correlated response.

Finally, I want to note that this really does confirm that as an overall trait controlled by a relatively small number of genes pigmentation in the lightening direction has a huge mutational target on it. Remember that East and West Eurasians are light skinned for different reasons. And in regards to skin color, an interesting point is that Melanesians, in particular Solomon Islanders, are amongst the most genetically similar to Africans when it comes to variation on these loci. TYRP1 is quite the exception.

Citation: DOI:10.1126/science.1217849

Citation: DOI:10.1111/j.1469-1809.2006.00341.x

Image credit: Graham Crumb

MORE ABOUT: Blonde, Blondism, Melanesian
  • Justin Giancola

    “East and West Eurasians are light skinned for different reasons.”

    Maybe by different means would be more precise; they could be for the same
    “reasons, ie. pressures.

  • http://nextgenseek.com nextgenseek

    Nice work and interesting post. just wanted to highlight that “Tyr” family of genes are involved in pigmentation. For eg, Tyrosinase is a well known gene for albinism. http://ghr.nlm.nih.gov/gene/TYR

    Nice to see a case where it makes total sense.

  • Sandgroper

    Now I can lay to rest those bullsh*t stories about shipwrecked Dutch sailors.

  • Don Mitchell

    I’m amused to be commenting here on this study, because back in 1988 Discover magazine printed some of my Solomon Islands images, including one of some blond-haired kids from the Lau Lagoon on Malaita.

    I’m an anthropologist who worked as a physical anthropologist on Malaita (Lau and Baegu) for a short time in 1968, and as an ecological anthropologist on Bougainville for a much longer time in the late sixties and early seventies.

    I looked at the Science article online, and I also looked at the supplementary materials.

    I was saddened to see no historical context. Of course that doesn’t detract from the interesting and significant conclusions, but I saw no references to prior biomedical/physical anthropological work in the Solomons. The Harvard Solomon Islands Project collected much data (anthropometry, skin color, blood, and more) on Malaita (Kwaio, Lau Lagoon, Baegu) and also on Bougainville (Nasioi, Nagovisi, Aita) and elsewhere in the area.

    I made the skin color measurements (and did some of the anthropometry) of the Lau and Baegu. I mention this because I have vivid and unhappy memories of struggling with the spectrometer I had available — an balky device from the British company EEL. I hope that their modern device was easier to use.

    I also failed to find information about how they assembled their subjects. Having been involved in (and in one case, in charge of) assembling population samples in the Solomons, I’d really like to know how they assembled their sample. This isn’t a criticism, because they had a wonderful sampling of the geographic area (though very heavy on the Malaita and Central regions and surprisingly light from Guadalcanal). Did they visit each location? I’m guessing that they did not, but if they did then that’s a major achievement and I’m surprised they didn’t report it. I’m not suggesting that their conclusions might be invalidated by sampling problems — this is just a matter of interest.

    I was also surprised to see no mention of Bougainville island, which is in every way (except politically) a part of the Solomons. From one of their sampled areas (Shortland) it’s only a few kilometers to southern Bougainville. Of course the political situation would have made it impossible to sample Bougainville, but I do think this should have been mentioned. My Bougainville research was in west-Central, rather than in the south, but there were no blond heads to be found there, and I can’t recall seeing any during my trips to the Buin region (very near the Shortlands), nor among the Austronesian-speaking Banoni.

    I had better say again that this isn’t criticism of their work as published, except perhaps for the lack of sampling information. Their work neatly solves a problem that’s been around a long time, and I’m very happy to see it solved.

    However, Razid, I’ll take issue with your statement “That is, having blonde hair is not correlated with a different ancestry in these Melanesian populations.” That’s accurate only if “these Melanesian populations” = “the sample,” because, as is obvious, the largest of the geographic Solomons (Bougainville, with its 200,000 people) is excluded from the sample.

    I’d also argue that Table S1 (online Materials and Methods) strongly hints at regional differences in the frequency of 93C. Notice the very high frequency (.49) for Malaita, the low frequency (.11) for the Polynesian Outliers, the very low frequency (.05) for Choiseul (in the north, near Bougainville) and the relatively low frequency (.20) in Western.

    I don’t think it would be difficult to argue for the existence of a SE-NW cline, and if that were the case it would need explaining at other than the molecular level.

    To me this is all a demonstration that an unequivocal solution at the molecular level doesn’t necessarily answer interesting questions at a higher level. Clearly the authors didn’t intend to tackle these questions, and so once again I say this isn’t meant as criticism.

  • Justin Giancola

    …no Sandgroper, now it is the Ancient Nordic Phonecians – after the Nordics moved from Sumer – who first arrived in Oceania after building Great Zimbabwe! blonde hair comes from mixing with the ancient alien gods which only Aryans did…

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #3, someone just posted a comment that this is obviously due to mixing within europeans. i put them in spam.

    “That is, having blonde hair is not correlated with a different ancestry in these Melanesian populations.” That’s accurate only if “these Melanesian populations” = “the sample,” because, as is obvious, the largest of the geographic Solomons (Bougainville, with its 200,000 people) is excluded from the sample.

    i mean melanesian vs. european ancestry. i assume there’s variation in this trait across oceania. i thought that was pretty obvious from my post?

  • Sandgroper

    There were plenty of Dutch sailors shipwrecked off the coast of Western Australia, but to anyone who knows the geography and the people, the idea that one of them could have made it to the western desert in order to transmit his blonde hair genes (but nothing else) is just about as bizarre as that – that hasn’t stopped the stories persisting and being retold with great assurance, including by a lot of people you might think should know better. Likewise the idea that little Aboriginal kids with snot running from their noses and flies clustered around their eyes were selectively and secretly engaging in some kind of cultural practice using chemical agents they had no access to in order to lighten their hair on their heads and forearms was equally always self-evidently a non-starter.

    It has been evident to me since I was a young kid that this was natural, but you can’t tell people stuff. I’m just pleased that it has finally been settled in the Solomons and that the obvious answer can be inferred in the case of the western desert Aboriginal people. Confirmation would be nice.

    It would also have been nice if the work Don Mitchell was involved in had been mentioned.

  • Sandgroper

    BTW, thanks for blocking that comment, Razib – I think it would have been enough to make me go ballistic at this point.

  • Don Mitchell

    It wasn’t obvious to me, perhaps because I processed “in” as “within,” and because I was thinking of the long and contentious history of untangling biology and language in the Solomons (and elsewhere). I refer to the debate about whether Austronesian- and Non-Austronesian-speaking populations significantly differ genetically — a debate that I don’t think we want to bring into this discussion.

  • Sandgroper

    Don, I’m tempted out of curiosity to ask if they do or not, but I’ll take the hint and not do so.

  • Don Mitchell

    If I told you, I’d have to kill you.

    But seriously. I’ve been out of the game for a long time, and I’m not sure how the balance of power sits these days, both with respect to evidence and loudness of voice.

    I left that part of anthropology a good 20 years ago. I’m using my real name here, so I may as well link to my small website http://www.wiasi.net where you can find a CV and links to what I have been doing.

    You can email me if you want to know what I know about it.

  • Sandgroper

    Thanks mate. Sorry to be a pest.

  • Rosanne Spector

    In reference to Don Mitchell’s comment about assembling the subjects: Two of the researchers on the paper – Sean Myles and Nic Timpson – spent about a month going island to island, explaining their study (in Solomon Islands pidgin), assembling subjects and gathering the samples, which numbered more than 1000. I’m a writer at Stanford and spoke with Sean for our blog: http://scopeblog.stanford.edu/2012/05/blond-hair-evolved-more-than-once-and-why-it-matters/ and for our newspaper: http://med.stanford.edu/ism/2012/may/blond.html. I included some details about their work on the islands in my articles. You’re right, it was incredibly interesting and my articles only scratch the surface. Their whole trip would make a great story.

  • Don Mitchell

    Thanks for the information, Rosanne. My BA is from Stanford, as it happens.

    That must have been an interesting and probably difficult month for those two guys.

    Encourage them to write that story.

  • Justin Giancola

    It would be interesting if they would look at Europeans who keep very fair hair into adulthood vs. those that have yellow hair as children – which includes many who won’t have fair hair as adults. My brother for instance had platimum hair as a child which eventually became a medium brown, and at peuberty all his hair turned black – eyebrows included. Stories like this go beyond a little “ripening with age” and yet is extremely common, and many people, like mine, don’t have fair haired parents nor strong accumulation of fair haired adults in their nearest relatives.

    Mechanisms aside, I think the cause of this phenomenon is rooted are archaic admixture. It really seems there is a lottery in what genes you get too, even different populations favoring certain genes and with some being recessive I think there’s a of explaining power.

    The denisovans were so far only found much further north; I think when we get a better look at their genome we shall find they were similarly depigmented like neanderthals.

  • T. Kosmatka

    Justin, I’ve been curious for a while about why some blondes darken and some don’t.

    My own suspicion is that the Val60L variant of MC1R might be involved in the differentiation of these two different kinds of European blondes. (and just like that, you have to throw the word “European” in front of the word blonde from now on and until the end of time) MC1R is more famously associated with red hair, of course, based on the Rs1805007(a.k.a., Arg151Cys), Rs1805009 (Asp294His), and Rs1805008 (Arg160T) variants. But another variant, Rs1805005(Val60L), is associated with blondeness. Compound heterozygotes of any of the three red-hair alleles produce red hair, and homozygotes of Val60L seem to produce blondes. I’m curious if a compound heterozygote of Val60L with either ARG151, Asp294, or Arg160T might produce blonde hair in children that eventually darkens with age. Or perhaps these compound heterozygotes produce the form of blonde hair that tends to stay light over the person’s entire life?

    Regarding the new form of blondness finally identified among island oceana, bravo. I’ve been waiting for this result for years, so it was nice to see it finally nailed down. Now it’ll be interesting to track down exactly how old the allele is and where it first came from. Have the Denisovan’s been checked for this yet?

  • Justin Giancola

    Also yellow haired children are much more widely dispersed geographically in Europe than significant numbers of
    similarly fair haired adults.

  • Justin Giancola

    Also, yellow haired children are much more widely dispersed geographically in Europe than significant numbers of similarly fair haired adults. It is awfully similar to Oceania.

  • Chuck

    “As a small child … I would wonder… the questions then were simple: was this trait an independent occurrence of de-pigmentation in Oceania, or was it due to introgression of European alleles?”

    Uh…how small of a child were you when asking these questions?

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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