*(means white skin, like you didn’t know that)

A mutant version of SLC24a5 is the biggest single cause of light skin color in Western Eurasia. It’s very widespread:


The usual explanation is that light skin ( in Western Eurasia), caused by this variant of SLC24A5, a variant  of SLC45A2, and a few other loci, is a product of selection for increased vitamin D production in areas with low levels of UV radiation.  It also seems likely that being too pale in a sufficiently sunny land would lead to problems, like skin cancer.

But this mutation wasn’t common in the old European hunter-gatherers: it may not have existed at all. While it was probably common in the Sardinian-like farming populations that apparently originated  somewhere in the Middle East – Otzi had it.

But you know, this mutation exists at pretty high frequencies in places that seem sunny. Its gene frequency in Moroccans is 90%.  In Egypt, 88%.  Libya, 92%. Saudis, 95%.  47% in South India. It’s 50% in Sinhalese, right on the equator.


In pure East Asians, and Amerindians, it’s apparently unknown.  It’s rare in most of Africa, but you do see it in places like Ethiopia (55%) and peoples like the Masai (27%).

It’s 7% in the San, but we know who to blame for that, don’t we?

So: although this mutation may help with vitamin D in Copenhagen or Tullamore, that can’t be the reason for such high frequencies in North Africa or India.

SLC24a5 does something other than confer more vitamin D: something that resulted in  tremendous fitness advantage.

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62 Responses to Tar-Zan*

  1. “It’s 7% in the San, but we know who to blame for that, don’t we?”

    We don’t all know, but we want to! Who is to blame? (I’m your most ignorant fan and follower, but am slowly getting better!)

  2. jamesd127 says:

    The clothing worn by Saudis suggests that this gene has serious disadvantages in the tropics.

    Do we know that this gene came out of the middle east? Looks to me that it is a white race gene, and the middle east is a cline between whites and blacks – that this gene is far above equilibrium levels in the middle east due to waves of conquest and migration, being carried into the tropics by genes for intelligence and cooperative behavior that are not necessarily associated.

    The strongest and most anomalous tropical extent of this gene is into India, which may well reflect the Aryan conquest, rather than any selective value of the gene.

    • gcochran9 says:

      The Middle East is a not really a cline: you find African admixture where the slaves landed. Relatively recent – you don’t see much in socially isolated groups like Jews or Alawites or Christians. And the gene does look as if it originated somewhere in the Middle East – more varied there. So no.

    • The fourth doorman of the apocalypse says:

      The clothing worn by Saudis suggests that this gene has serious disadvantages in the tropics.

      Hmmm, at approximately 25N, Saudi Arabia hardly seems to be in the tropics. It straddles the Tropic of Cancer and even Mecca is only a little south of the Tropic of Cancer.

    • Lesser Bull says:

      In extremely dry climates, more clothing can be beneficial for evaporative cooling.

  3. Howard says:

    So: although this mutation may help with vitamin D in Copenhagen or Tullamore, that can’t be the reason for such high frequencies in North Africa or India.

    Couldn’t it have originated elsewhere and then be brought to North Africa and India later?

  4. as says:

    Does it give you more resistance to an infectious disease? One which Amerindians don’t get?

  5. tomas says:

    What’s with writing all mystery like and the open questions here, are you just waiting for a follow up post? Surely it makes no sense to suggest this substitution mutation produces multiple phenotype effects besides skin color, or is that a momentary lapse forgetting other hypotheses. I thought the more usual and not at all novel explanation everyone has already heard was that runaway sexual selection can account for such alleles spreading within relatively few generations.

    Modern humans are somewhat sexually dimorphic on skin tone among other aspects of physical appearance and related behavioral preferences and no one serious pretends ancient human populations couldn’t have been either. So the selection benefit regarding skin cancer and ultraviolet light absorption needn’t have been that significant, true, but coincidental preference for lighter skinned females or something like that follows to produce an obvious result. The same goes for other human populations with different genes behind their skin tone and other appearance traits. Wouldn’t require a huge environmental fitness change when it was possibly just sexual selection and otherwise typical population dynamics.

    • gcochran9 says:

      Most genes are pleiotropic – it makes every kind of sense to suggest that some other effect might be the main advantage, since nobody needs extra vitamin D in India or North Africa.

      Consider EDAR: it makes shovel-shaped teeth, extra eccrine sweat glands, smaller breasts, increased scalp hair thickness, and who knows what else. Nobody knows what drove its increase.

      Looking at its distribution, It is obvious that SLC24A5 has some positive effect other than paleness, which is obviously why nobody has every looked for one.

      obvious. obvious. obvious. OBVIOUS.

      • Howard says:

        Could it be lactase persistence?

      • tomas says:

        Oh, I completely grant that your insight is spot on and the politically correct just-so stories that something like this is “only vitamin D” isn’t a full story. It just seems like sexual selection is roughly the “default” hypothesis which deserves a mention and a strong reason to discount. It’s quite possible in reporting, publication, and other news from all the sequencing these days and studies of ancient remains that some of the politically correct crowd does neglect to mention it because they aren’t comfortable with that aspect of human evolution, or charitably it can innocently be overlooked.

        Sexual selection also robustly offers an explanation for how skin tone and as often hypothesized many other appearance traits like hair color could have changed over time (and quickly) in any human populations. I’m not in the camp to assume impactful and unexplored secondary effects to all surviving mutations while sexual fitness is a good possibility. Could be true here, technically your remarks are very precise and expertly raised, I should say that the counter-hypothesis is to assuming any secondary mutation effects must have been what provided the large benefits to fitness. It would seem more improbable to suppose that in every case, say different genes for lighter skin in East Asians also produced large, unknown other benefits and differently from the hypothetical unknown benefits from light skin genes in West Eurasians.

      • tommy says:

        @Howard: Unlikely. Otzi had it after all and he is thought to have been lactose intolerant. Otzi was certainly a consumer of our Mideastern cultivated grains like wheat and barley.. Of course not all dairy contains lactose and Otzi is often thought to have been a shepherd. Perhaps it could pertain to the body’s utilization of fermented lactose-free dairy products. So maybe there remains a biochemical connection there somewhere with Vitamin D aside from UV light.

  6. Difference Maker says:

    That lightest shade in Europe looks like the ancient Celtic distribution

  7. j3morecharacters says:

    Recent studies in sunny Israel have found surprisingly low vitamin D levels: higher in Ashkenazim than Sephardim who, in turn, had higher vitamin D levels than Arab subjects (31.4 +/- 12, 24.1 +/- 10, and 17.6 +/- 9 ng/ml respectively). With regard to season, there were no differences between the samples collected in winter and the samples collected in summer. Solar irradiation levels (and skin colour) seem less relevant than covering the body with cloths. Here doctors are advising Vit. D supplements to everybody.

    A probable side effect of the conversion of Africans to Christianity (and the Islam) will be the whitening of their skins in a few generations.

  8. SpaghettiMeatball says:

    It’s sexiness, duh. Men like to bang light-skinned girls.

  9. TWS says:

    Two related questions. What are the ‘+’ signs. There is a cluster near the Hopi or maybe Navajo etc. And if it does have a fitness advantage is it possibly related to IQ? If so then _no one_ will be looking for a possible advantage. Too damn much of that hbd stuff coming out as it is.

  10. RS says:

    In addition to skin cancer, there’s also apt to be a problematic degree of photolysis of folate — or likely so — at least according to Jablonski or whoever.

  11. panjoomby says:

    uhh could it add to intelligence?

  12. Anon says:

    Didn’t those domesticated foxes get lighter? Maybe it’s a side effect of domestication. My thought is that in Europe people needed to wear clothes all the time due to the cold so they didn’t need the pigment, like how those fish that live in caves turn pale. Do the inuit have paler skin than other Native Americans?

  13. Patrick Boyle says:

    Yes the foxes got lighter. Rushton’s last major paper was on the melanocortin hypothesis. He points out that dark skin (or should I say integument) creatures are almost always less aggressive than light skinned ones. That’s trues in mammals, reptiles, fish, birds and insects.

    Excessive aggressiveness is an impediment to social organization so maybe those people who became lighter also became more docile and civilized. That would seem to fit the facts as you have described them. Greater ability to live in groups would seem to be adaptive and genetically advantageous.

    • misdreavus says:

      If melaninism were true (at least for our species), why haven’t these alleles showed up in a GWAS? We already have a decent understanding of the genetic architecture of skin color.

      • gcochran9 says:

        If, hypothetically, you did a GWAS study of trait X in a population that was fixed for a given allele, that allele would explain zero percent of the variance in trait X.

        The light-skin version SLC24a5 is essentially fixed in Europeans, over 99% frequency.

        We have mixed populations in which that SLC24a5 allele is not fixed, but it may be that some of of the more interesting GWAS surveys have never been done in such a mixed population.

        For a highly polymorphic trait like height, you could do a Visscher-style study to see how the trait varied with ancestry. That’s been done for some traits, but never for IQ, I think.

        Sticking my neck out, I would guess that in Pygmy population with a fair amount of Bantu admixture, IQ would go up with increasing Bantu ancestry.

    • Patrick Boyle says:

      I wrote ‘less’ when I meant ‘more’. My bad.

      This phenomenon is seen at the pound. Light colored or piebald dogs are quickly adopted. Black dogs are euthanized. Humans seem to instinctively prefer light colored dogs because they expect them to be more docile and loving. If this preference carries over to judging humans you have your answer.

      Melanocortin theory is as yet unproved. There is some contrary evidence (e.g. Black Labs). The genes that underlie melanin bio-synthesis are said to be pleiotropic, and also responsible for behavioral differences. But that connection is a long way from being demonstrated. I’m only suggesting that if there is anything to it, it does provide another reason for the spread of light skin in addition to Vitamin D.

      • SMERSH says:

        Not convinced dogs are a good example. Black Shelties, poodles, etc. Many dog breeds come in black because it’s an easy color to produce through selective breeding.

        Pit bulls and other aggressive gripping dogs come in light colors.

        Black cats have the same problem getting adopted that black dogs do and I doubt people fear violence from them.

        There could be a number of reasons why people find black animals less appealing. They don’t photograph well and they’re a little boring.

        Besides, dogs aren’t even a good way to prove or disprove the theory because of extensive genetic manipulation and selective breeding.

  14. Anonymous says:

    I’m guessing there are two reasons why this particular gene is at high levels in areas where light skin has fitness disadvantages. First light skin color was considered more attractive so light skinned people were more likely selected as mates and had more babies. Second there was back migrations into southern regions by populations that had this gene. Blondes have more fun, so did pale faces, prejudice towards dark skin is not new.

    • dave chamberlin says:

      the above comment was me. by mistake I made it anonymous

    • gcochran9 says:

      I’m guessing you’re wrong. This being a big, complicated world, the odds are on my side.

      • dave chamberlin says:

        My bad for not comprehending your earlier explanation. “It is OBVIOUS that SLC24a5 has some positive effect other than paleness.” It does make sense especially since other genes have multiple effects. People in bygone times would have believed that people that looked different than the group they belonged to were ugly. So my first guess that dark skinned people would have thought that pale skinned were more attractive is just flat wrong. But I still think my second guess, back migration by populations benefiting from hybridization of anatomically modern humans and neanderthals is part of the answer, but this admittedly is just speculation on my part.

  15. Yes, it is obvious. At first one may confound the argument with different gene flow patterns in human history, but that can’t be the case since no period of continual neutralism extends over say the last 40 000 years; natural selection has happened at different locations during thousands of years after that, whether one looks at Scandinavia, India or the Middle East.

  16. reiner Tor says:

    I’m sure that other advantage was White Privilege. This just goes a long way to show the history of white supremacism, slavery, the holocaust, etc.

  17. Greying Wanderer says:

    It’s the Caucasian distribution more or less? If it’s obvious from the distribution the advantage can’t be D deficiency yes – now you mention it, it is. If it’s meant to be obvious what the advantage is from the distribution I’m very stumped. I’ll pretend it’s the first.

    If it’s basically the (or at least a) Caucasian gene and it developed in the mid-east (Arabia?) originally and Caucasians spread from there all over the place then it must do something quite important relative to SSA but be matched or even over-matched by something similar that developed separately in East Asia.

    • Greying Wanderer says:

      Actually if it’s pleiotropic and the pale skin is a side-effect of something else doesn’t that mean the pale skin could still be selected for separately on top of whatever the original reason was i.e. even if the main effect has nothing to do with sexual selection the side effect, pale skin, could be sexually selected for as well or a vitamin D deficiency effect could be selected for as well in certain regions?

      (That doesn’t change that there must be another factor just that you might expect the white-est people where one or more of the other factors apply on top of whatever the main one is.)

  18. BB753 says:

    Could this light sin general be correlated with increased ability to digest wheat and other cereals?It seems to spread from the Middle-east and follow early farmers around West-Asia.

    • gcochran9 says:

      I could imagine that. Mouse knock-in studies might tell us something useful.

    • The fourth doorman of the apocalypse says:

      Northern Chinese, who it seems from the intro above, lack this gene, seem to have no problem digesting wheat-based products.

      Sure, the Southern Chinese eat lots of rice, but Marco Polo got the idea for pasta from the Northern Chinese, I am told.

      • IC says:

        Yes, wheat is major food for northern Chinese, including all those wheat flour based food(noodle, dumpling, baozi, shaomai, steaming bread,ect) in Chinese Resturant. A lot of northern rural farmers even never saw a rice in their life. North is too dry for rice growing.

        As rural farmer boy, I never saw rice until I moved into city later in life.

      • Patrick Boyle says:

        You weren’t told that about Marco Polo. You saw it in the movie. Gary Cooper asks his Chinese hosts what these things are that they are feeding him. They say ‘spaget’. LOL.

        There were noodles in Germany hundreds of years earlier. The Chinese at that time were probably the most advanced civilization on earth but they didn’t invent pasta.

        Because of the very anti-American Joseph Needham you should always be skeptical of claims about Chinese accomplishments.

      • Ben says:

        Needham was a classic eccentric Englishman. Not only was he a communist, he was also a fervent Christian, a Morris dancer, and a nudist. He seems to have been driven by eccentric tastes and curiosities rather than visceral anti-American feeling.

      • Sandgroper says:

        The first grain farmed in China was millet. The earliest evidence of millet consumption in China is 12,000 years old (that’s consumption, not necessarily agriculture), but there is clear evidence for farming of millet by >9,000 years ago. In the north, the staple is now wheat, together with millet, sorghum, and (post-1492) corn, potatoes and sweet potatoes. Hill rice is also grown in the north, but it is very scarce, expensive and lousy.

        Oh not the stupid “who invented spaghetti” argument again. The Romans had pasta, they used it as a way of preserving flour for sea voyages. It seems very likely that pasta/noodles were invented independently in Europe and China – the stuff is not exactly difficult to make. Just like agriculture developed independently in different parts of the world.

      • The fourth doorman of the apocalypse says:

        You weren’t told that about Marco Polo. You saw it in the movie.

        I don’t recall seeing that movie.

        I would not be surprised that Needham spouted such shit, as he did in many other areas where it concerns the Chinese.

        I just add his pronouncements to such things as “Arabic numeral” and the claims for Arab priority in the invention of just about every area the Greeks already had explored.

  19. BB753 says:

    Typo: light skin gene

  20. I will gladly cop to being perennially unable to see the obvious – which is why I am still Assistant – but will note that everything seems obvious once you have seen it. Holmes mentions that at least a dozen times – “The Red-Headed League,” for example.

  21. Greying Wanderer says:

    dave chamberlin
    “So my first guess that dark skinned people would have thought that pale skinned were more attractive is just flat wrong.”

    I’m not sure attraction has to be conscious e.g. a fat woman in a corset has the same effect on me as a slim woman.

    Personally I wonder if pale skinned females might display ovulation signals better.


    Looking at the distribution: it started somewhere and then spread – so far so obvious – but given that it must have had an advantage it could have started anywhere and spread anywhere it wasn’t contested by an equally strong effect so it doesn’t have to have started anywhere in particular e.g. just outside Africa which was my first thought.

    It gets contested in Africa and also to the East with India as the border zone. Assuming it’s kept out of Africa for straightforward sun reasons what might contest it in East Asia – a mirror effect i.e. East Asia has a different gene with the same effect?

    If you look for the center-point of the distribution and weight it a bit to the south-east for assumed relative population density reasons I’d say it comes out somewhere near the Black Sea / East Anatolia – which looks very Basal Eurasian.

    So, if it started somewhere recently out of Africa i’d be inclined to pale skin / long hair = ovulation signals / sexual selection and if so then the contested version would simply be the East Asian lighter skin gene.

    If it started more towards first farmers then something to do with that and the East Asian version would mirror it – which kinda makes me think they would have needed to independently figure out farming?

    Thinking aloud – prob wrong.

    • Greying Wanderer says:

      Although if it was a just out of Africa thing it should have effected the mesolithic foragers so pointing at farmers again.

      To be equally contested I think it would still need to be mirrored by an East Asian version of the same thing. Diet? Tame? r/K?

    • erica says:

      “Personally I wonder if pale skinned females might display ovulation signals better.”

      Do females in some population groups have longer windows of fertility than women in other groups? Different menstrual cycle lengths?

  22. RS says:

    > Do the inuit have paler skin than other Native Americans?

    I don’t think so, not by very much, but this is on the basis of my having known one pure Inuit.

    However, I believe Jablonski — your ‘classic’ theorist of vitamin D, folate, and skin — probably explained this on the basis of their eating of fatty fish, which I believe are richer in vitamin D than animal food in general is. I think she said this about the Welsh too. But not all these people lived on the coast, so I would like to know how preservable fatty fish is for trade under primitive conditions. The fat may obstruct the egress of water, but I’d guess any meat can be dried if you slice it thin enough. I’m not a hunter but I understand thin slicing — as opposed to smoking big pieces of animal — is the simpler and more robust technique, though probably more laborious. I think you basically slice up, dry over a fire, viola.

    Also, why aren’t coastal and near-coastal Norse, or whatever, as dark as Welsh from the same habitat?

    Cochran’s post I find convincing: her model has to be incomplete. However Jablonskism, and a fortiori P-Frostism, need not be mutually exclusive with other causes. Not that they are all necessarily substantially right — it’s possible though.

    I would contribute this: we can guess why the allele under discussion doesn’t do so well south of the Sahara, but why didn’t it go further east? My guess is “they already had something for that” over there, hence much less positive selection on the allele. But what is “that”, what is X — is it skin tone, something else, or more than one thing? Well, plenty of derived alleles and traits in E Asia of course, so, no surprise if they already had X under control in their own style.

    • RS says:

      Then again, my beef jerky invariably comes with a desiccant pack, so how, in early times, do you keep dried meat dry in a humid environ? Lot of salt or something, and dry it harder in the first place?

      Note, if you are health-conscious you actually shouldn’t eat preserved meat according to what I’ve heard. The orthodoxy (of late) is that fresh meat is a healthier proposition.

    • Greying Wanderer says:

      “Also, why aren’t coastal and near-coastal Norse, or whatever, as dark as Welsh from the same habitat?”

      If people from the North Wales mountains are a (relatively) very aboriginal stock then if the epicenter of the light skin distribution is more East Anatolia than Levant then the PIE from around the Black Sea would have been very close to the epicenter and may have spread it at the same time as the farmers – and more so to Scandinavia than Wales.

  23. Greying Wanderer says:

    It could be a fluke but if Caucasian used to extend all the way to Siberia in the far north then might that mean the East Asian variant of (whatever this gene does that’s so important) is better at high latitudes?

  24. Greying Wanderer says:

    Another random thought (apologies) on the distribution

    Lactase Persistence

    Could LP have originally started as simply switching it off later i.e. allowing later weaning?


    (google guesses so quite possibly wrong)

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  26. Tom says:

    How healthy is vitamin D supplementation? James Watson said antioxidants and vitamins might not be that good for you.

  27. Dipitty Do says:

    I don’t know if you read comments on old posts, but I was thinking of this independently before I began reading through your archives, and have a theory. Now, I am not a geneticist or a biologist or anything relevant, so I may be totally wrong in ways I can’t even imagine, but here is my theory:

    Vit.D production and brain functioning (and brains themselves) both involve cholesterol. VitD itself is probably an important factor in brain functioning. Something that makes it easier for the body to produce, store, process, use, etc. cholesterol and VitD might also make it easier/more efficient for brains to use cholesterol and VitD–that is, increase brain function.

    I was thinking about this in context with researching Alzheimer’s (I unfortunately have one of the high-risk Alzheimer’s genes,) and some articles that claimed that the “Alzheimer’s gene” codes for inferior cholesterol uptake in the brain. If inefficient uptake leads to degeneration, more efficient uptake could be positive. Likewise, I read about a study that found that people with lower VitD levels had far more Alzheimer’s, but I haven’t read the original so of course I don’t know how or if they controlled for confounders. I recall as well some posts on Peter Frost’s blog about the ability to produce/store VitD, which appears to also vary predictably. People who can easily store up an excess of VitD in the summer may pass that excess on to gestating fetuses (with the caveat that winter-fetuses might not do so well.)

    Reversing our causality, if cities and agriculture emerged first in the Mid East, and this put pressure on people to develop new mental traits/increase their abilities, then any trait that increased the availability of brain-building nutrients (or whatever we want to call them,) could be selected for, even if it had a side effect of requiring you to wear clothes or burn. The trait could really flourish, though, in places where burning wasn’t such a concern.

    If I’m correct, this seems like just about the least-PC genetic finding I can think of.

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