Korak

If the common mutation of SLC24A5 confers an advantage other than increased vitamin-D production, evidence might show up in a mixed ethnic group, formed from one population with a high incidence of the interesting SLC24A5 variant and another with little or none. You could look at the overall admixture fraction – say, 50% African and 50% non-African – and see if the SLC24A5 variant is more common today than you’d expect from the original admixture  proportions (which will be easily determined from looking at neutral loci).

This has already been done for Ethiopia.  There, in the Semitic and Cushitic populations, where the estimated proportions of African and non-African ancestries are approximately equal, SLC24A5 is significantly more common than you would expect.

Those populations live up on the plateau, over a mile high and within ten degrees of the equator.  There’s enough UV to roast a goat.  Somehow I doubt if Vitamin D is paying the freight here.

As for those who assume that sexual selection must be driving that increase – show me the time machine.  I don’t know if there was any such preference over the past three thousand years in Ethiopia and neither do you.  This is used as an excuse to avoid looking at the biochemical details and trying to find out what’s actually happening.  If I hear it again, I may have to call the elephants.

Next, someone should do the same for the Deccan plateau, which ought to be easy.

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51 Responses to Korak

  1. tommy says:

    Sexual selection as an end to itself seems like a just-so story to me in most cases and especially where females of the species are concerned. Sexual selection doesn’t explain the reason why some traits would be sexually preferred in the first place. Lets say a copy of a gene was deleterious but preferred, all things being equal, you’d think before long a mutant would arise that didn’t prefer the harmful copy and that mutant would be the progenitor of the future. I’m especially skeptical of sexual selection hypotheses based upon female attributes for that reason: I can entertain that the female, being the rate limiting sex in terms of reproduction, may be able to nudge the males of a species down a certain evolutionary corridor, even a ridiculous one, but the mutant male who can freely propagate with otherwise fit females his peers overlook is going to spread his genes rapidly. Maybe this explains why coloration and plumage changes among male birds are among the most frequently cited examples of sexual selection.

    • Boris Bartlog says:

      Except that in a species that has had quite a lot of pair-bonding/monogamy, going back tens of thousands of years, that mutant male can’t necessarily propagate his genes rapidly; and being the sexiest girl in the tribe is still advantageous unless or until *all* the males are equally indiscriminate. Still I broadly agree with your thesis. Sexual selection on the female side mostly seems to result in not-very-costly exaggeration of features that were already dimorphic (selected) for functional reasons. That doesn’t by itself rule out the possibility of pale skin being selected for on the female side, but in the case of SLC24a5, I think the question is: Why *then*? Why *there*? If the distribution were more consistent with the vitamin D hypothesis, I’d think clothing and shelter might have been drivers; people spend less time with the sun on their skin, they need to become paler to keep up vitamin D production. But with the reach extending into Ethiopia, I think that’s ruled out.

      • Greying Wanderer says:

        “Except that in a species that has had quite a lot of pair-bonding/monogamy, going back tens of thousands of years”

        Well, that’s the thing, did they all? Personally I wonder if one of the biggest changes out of the tropics would be something r/K related that would start to *produce* pair-bonding/monogamy.

    • Richard Sharpe says:

      I’m especially skeptical of sexual selection hypotheses based upon female attributes for that reason: I can entertain that the female, being the rate limiting sex in terms of reproduction, may be able to nudge the males of a species down a certain evolutionary corridor, even a ridiculous one, but the mutant male who can freely propagate with otherwise fit females his peers overlook is going to spread his genes rapidly.

      While I don’t think that sexual selection explains skin color, there seems to be some problems with your arguments.

      1. Why would those males being selected by females leave any unimpregnated women for the unselected males?

      2. There is more to reproductive success than fucking. Your offspring, if any result from your sexual athleticism, have to survive and reproduce as well.

    • Greying Wanderer says:

      “I’m especially skeptical of sexual selection hypotheses based upon female attributes for that reason”

      Red baboon butts signal ovulation very clearly. If redder lips when ovulating are a human equivalent then a lighter skin color might increase the contrast thus increasing the effect.

      Although I’m not sure if something like this technically counts as sexual selection which may be a source of confusion.

    • tommy says:

      @Boris Bartlog: I think you’re right that sexual selection can theoretically happen in regards to females any time there a resource commitment is demanded of the male to his offspring. This obviously limits any male’s opportunities for reproduction, but given that a male can always potentially resort to promiscuity as a strategy, and a less valued but still fertile female benefits from such promiscuity, then I have to imagine it tends to be a far weaker force in nature than sexual selection when it comes to male attributes. Primates, like ourselves and chimpanzees, and unlike some birds, are hardly models of sexual fidelity and I highly doubt that light skin color is going to be explained by sexual selection, but given that we’re a highly k species on the r/k spectrum, that small average difference between male and female skin color our species might be explained by such a mechanism.

      @Richard Sharpe:

      “1. Why would those males being selected by females leave any unimpregnated women for the unselected males?”

      I’m not talking about the selection of males here, but rather the selection of females by males. Fully fertile females who are less desired by males for reasons having nothing to do with functionality would seem to be easy pickings for a promiscuous and fully fertile male and both the male and female parent ought to ordinarily increase their reproductive success via such promiscuity. As I admitted ,above, pair bonding and resource commitments to offspring may indeed limit this to some extent and, while I suspect it’s fairly weak, perhaps I underestimate that force. In any event, it’s an interesting topic.

      • The fourth doorman of the apocalypse says:

        Hmmm, I think you misunderstand sexual selection …

        As I understand what Frost is saying, it is that there was selection on females to stand out when there was intense competition for males (because males died during hunting and because males could not easily support more than one mate and her offspring.)

        Thus, he claims that lighter skin color as well as different hair colors and eye colors made females more attractive because initially they were novel and scarce and the male phenotype is being dragged along by the female phenotype. Ie, that such females were more successful at leaving offspring.

        It seems possible that it could have occurred. However, my objection is, I guess, that it is not clear that a novel characteristic is a good indicator of good reproductive value.

      • tommy says:

        Yes, that would be my major objection as well: most novelty isn’t a good thing. A person carrying a gene granting them green or blue skin would certainly be novel but, with the possible exception of Captain Kirk, I don’t think we’d find it especially attractive.

  2. Sandgroper says:

    *applauds*

  3. neilfutureboy says:

    Nope looks like it confers some advantage other than vitamin D except that makes no sense.
    Could there be another beneficial gene so close on the DNA that they are inherited as a pair? That doesn’t sound any more likely.

    The background radiation in the Deccan is way up there – as high as 150 mSv when the official danger level is 15. If the theory is right that should mean at least an awful lot of mutation, not to mention cancer deaths, but the latter isn’t happening (indeed there is some evidence for hormesis – that radiation is beneficial) and I suspect the mutations won’t be either if somebody looks

  4. dave chamberlin says:

    Don’t send the heffalumps after me, I already ate my words about sexual selection playing a roll. Just wondering, it is obvious that very pale skin would be a serious disadvantage down yonder where the sun gets straight over your head. But what about very dark skin? Wouldn’t that also be a disadvantage? I hate to be the fly in the ointment but last time I worked outside on a 90 degree day with a dark tee shirt on I damn near got sun stroke. So…..maybe the optimum color to be when you evolve in goat frying territory is a golden brown.

    • Boris Bartlog says:

      It doesn’t seem to be a disadvantage in terms of overheating, if that’s what you mean. Protection against UV burns and also folate destruction is way more important than whatever tiny advantage light skin would have in terms of absorbing less heat.

      • dave chamberlin says:

        I see your point. I have read that this sweep of the SLC24A5 gene occurred 11,000 to 19,000 years ago. I would think by then I another obvious choice for protection against UV burns and folate destruction would have occurred making dark pigmentation less important. But I have no clue when people started wearing hats and clothes to protect themselves from the sun, does anybody?

  5. Slate Slabrock says:

    Couldn’t it simply correlate with other beneficial traits and function as a visual indicator of the presence of those traits?

    We can *almost* see this in African Americans. Light skinned African American females are more desirable because light skin correlates with European (and, coincidentally[1], Neanderthal) ancestry and European ancestry is correlated with all sorts of traits that are quite beneficial for life in the United States.

    Light skinned African American males aren’t necessarily more sexually desirable, but because (on average) they have more European ancestry than dark skinned African Americans they, have, on average, an enhanced capability to make their way in a society that rewards European traits and thus they are more likely to obtain high status and material success which should, in theory, increase their reproductive fitness.

    It doesn’t quite work out that way though. The high status and the material success is there, but the kids aren’t. But then, that’s not too surprising given widespread dysgenic fertility in Western societies and loss of interest in maximizing reproduction among the higher status and more materially successful parts of the population. Generally it is assumed that modernity is unusual and that high status and material success correlated with reproductive success in the past. So the model isn’t looking too bad.

    I know it is possible that the genes for light skin could become de-linked for the genes for other behavioral traits, but would they necessarily do so? You can’t necessarily assume a “well mixed population”, hierarchies persist even in multiracial countries like Brazil. People are mixed, but not well-mixed; the correlation between light skin and European ancestry is reduced, but it is still high and it still corresponds with higher social and economic status.

    [1] I say coincidentally, because Neanderthals supposedly have a different light skin color gene than modern humans did. Still, light skinned modern humans have Neanderthal genes while Africans don’t.

  6. Inane Rambler says:

    Since Peter Frost has been the greatest voice I’ve seen in favor of sexual selection driving racial features, why don’t the two of you start a dialogue about this issue?

  7. TWS says:

    Ok, Tarzan being white is all well and good but why did Dejah Thoris have nipples if she laid eggs? And how do we get to barsoom? Because the mars I see pretty much sucks.

  8. Greying Wanderer says:

    http://www.washingtonpost.com/blogs/wonkblog/wp/2012/08/20/study-rape-victims-have-a-higher-pregnancy-rates-than-other-women/

    I don’t know if that study is correct or not but if it is then

    *If* rape is an r-type reproduction strategy and *if* light skin displays ovulation signals better than darker skin then that would both explain the study results and illustrate a clear mechanism for sexual selection on lighter skin – not very nice but clear.

    However if that was the mechanism then it ought to have started as soon out of the tropics as the balance in favor of darker skin was over matched implying
    -Capoids should have their own skin-lightening gene if it’s not this one
    -there’s a missing Capoid equivalent population in non-tropical northern Africa which was swamped later by a mixture of Bantu Expansion and back-migration
    -this variant, if it’s different to the implied Capoid one, ought to have developed somewhere close in geography or time to North Africa / Arabia

    .

    If it developed some way off and/or much later and especially if it developed where there was a sudden shift to much higher population density – either farming or very high density foraging – then i’d suspect it was a taming gene in some form as i don’t think adaption to a particular crop explains the Caucasian / East Asian dividing line – although maybe an adaptation to *crops* in general might do.

    • Greying Wanderer says:

      “this variant, if it’s different to the implied Capoid one, ought to have developed somewhere close in geography or time to North Africa / Arabia”

      rather if Caucasians don’t have the implied Capoid one and this is a substitute for it then it should have arisen close in time or geography. if Caucasians do have the implied Capoid one as well – if it exists – then they wouldn’t have needed this which would point more at another explanation e.g. taming, diet etc.

  9. Jim says:

    I thought the usual explanation of the preference of female birds for gaudy males is that the male’s gaudiness is signaling that he is in good health and so less likely to have genetic problems. I do think that sexual selection is probably secondary to functional selection. Perhaps women with larger breasts can produce more milk for their offspring which leads to direct selection which is then accentuated by sexual selection on the part of men.

    • The fourth doorman of the apocalypse says:

      Perhaps women with larger breasts can produce more milk for their offspring which leads to direct selection which is then accentuated by sexual selection on the part of men.

      No. It’s mostly fatty tissue. I like breasts as well as the next man because my genes have programmed me to do so, however …

      Clearly, what larger breasts are doing is manipulating the modules in men’s brains that respond to breasts, and larger breasts signal maturity (ie, that the holder can bear babies and are not immature females.) These modules clearly have never evolved a stop signal because there has never been a need because KK cups have been so rare in our evolutionary past.

    • Sideways says:

      You’d see it in every mammal, then. We don’t.

  10. SASorensen@gmail.com says:

    Have you already searched out the zebrafish paper?
    http://www.sciencemag.org/content/310/5755/1782.short

    What other published sources have you been looking at? For instance, a paper in PLOS seems to report a lot of haplotype data on North and South Indians. http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1003912

  11. The fourth doorman of the apocalypse says:

    Given it’s name as a Sodium/Potassium/Calcium exchanger 5, does it provide for a more efficient exchange/transport of those elements into or out of cells?

    Of course, you realize that this is just another unearned privilege that evil white people have.

    • The fourth doorman of the apocalypse says:

      Could it be improved neural functioning because improved transport leads to faster recharge times?

  12. The fourth doorman of the apocalypse says:

    If the big increase in the prevalence of SLC24A5 occurred after the start of large-scale cities and states, I would think it lead to better brain functioning. However, that raises the question of how East Asians are doing it.

    • The fourth doorman of the apocalypse says:

      However, they still claim that it is vitamin D related:

      http://www.chenglab.com/east-asian-skin-color/

      The dark skin of African populations, the ancestral state in humans, is protective in regions with high solar UV exposure. In contrast, the light skin of Europeans has a selective advantage in northerly latitudes due to higher sun-dependent generation of vitamin D.

      Maybe that’s so they can keep getting funding.

    • Greying Wanderer says:

      breast milk?

      • Greying Wanderer says:

        not necessarily more but for longer (origin of LP?) or better quality (EDAR?)

      • The fourth doorman of the apocalypse says:

        not necessarily more but for longer (origin of LP?) or better quality (EDAR?)

        Behavioral changes gets both and LP is likely a result of a group already using milk products (like fermented milk or cheese etc.)

      • The fourth doorman of the apocalypse says:

        Moreover, Southern East Asians solve their infants’ nutritional needs in a different, behavior-mediated way. They use rice gruel supplemented with proteins etc.

  13. Greying Wanderer says:

    fourth doorman

    “Behavioral changes gets both and LP is likely a result of a group already using milk products (like fermented milk or cheese etc.)”

    Sure later, but what about originally, what if the first step towards LP later was simply children being LT for a bit longer than previously?

    (And that change separately driving selection for LP later in environments where later milk drinking made all the difference.)

    As you say

    “If the big increase in the prevalence of SLC24A5 occurred after the start of large-scale cities and states, I would think it lead to better brain functioning. However, that raises the question of how East Asians are doing it.”

    A comment from

    https://westhunt.wordpress.com/2013/03/12/edar/

    “I can’t find any online data about overall production, but there’s one 1997 study that looked at its chemical composition. In that study, breast milk of Hong Kong Chinese women and women from a province in central China was compared against Western countries. Women from HK and women from central China had substantially different diets and different caloric intakes, but both groups had higher concentrations of long-chain polyunsaturated lipids DHA and AA than typical for Westerners.
    DHA in particular has a number of effects on brain development, it’s relatively hard to come by in the environment (its primary source is fish), and the efficiency of conversion of other polyunsaturated fats into DHA is low (except possibly in breastfeeding mothers.) If you have a gene that results in its greater concentration in breast milk, that will have a clear survival advantage in a society that subsists on a DHA-deficient diet.”

    vs

    LP distribution

    (nb not saying SLC24A5 causes LP but whether SLC24A5 effects something to do with breast-feeding hence the *subsequent* correlation with LP.)

  14. Greying Wanderer says:

    @fourth doorman

    “Moreover, Southern East Asians solve their infants’ nutritional needs in a different, behavior-mediated way. They use rice gruel supplemented with proteins etc.”

    Did they always?

  15. Greying Wanderer says:

    Just some wiki-ing, not saying it means anything necessarily

    http://en.wikipedia.org/wiki/Sodium-iodide_symporter

    “The sodium/iodide symporter (NIS), also known as Sodium/iodide cotransporter[1] or solute carrier family 5, member 5 (SLC5A5) is a protein that in humans is encoded by the SLC5A5 gene.”

    “Apart from thyroid cells NIS can also be found, although less expressed, in other tissues such as the salivary glands, the gastric mucosa, the kidney, the placenta, the ovaries and the mammary glands during pregnancy and lactation. NIS expression in the mammary glands is quite a relevant fact since the regulation of iodide absorption and its presence in the breast milk is the main source of iodine for a newborn.”

    .

    http://blogs.discovermagazine.com/crux/2013/07/23/how-adding-iodine-to-salt-boosted-americans-iq/#.UuVMRNLFL4Y

    .

    driving force?
    -coastal expansion = fish
    -moving inland = less fish

  16. Tom Bri says:

    Another question is, why right now? The timing interests me. If this mutation is so beneficial, why was everyone brown/black for all of human pre-history, (as far as we know)? Europeans were apparently brown at least until 7000 years ago, according to a post I just saw on Dienekes. Suddenly, they are all white. What suddenly changed 7000 years ago to make this variant start spreading? If I understand correctly, it is just a knockout mutation, so probably happening all the time, not a unique mutation that has only ever happened once.

  17. little spoon says:

    The question is still why Europeans and Near easterners became white less than 7000 years (possibly much less than 7000 years, right?). As for sexual selection, possible, but then you have to wonder why Indians are so dark. The Aryan invasion of South Asia and preference for Aryanness in Indian society is well documented and present on some level for thousands of years. Yet, after 3000 or 4000 years of that reason for sexual selection in preference for Aryanness, Indians are still one of the world’s darkest races. After white Eurasians penetrated into western Europe for thousands of years, Europeans almost universally went from dark to light. So why there?

    Ultimately SLC24A5 doesn’t explain 100% of skin tone variation and the variation in skin tone we see in ethnicities is pretty consistent with a combination of level of UV exposure and level of grain dependency in diet. I am not sure why an added dimension of sexual selection is needed to explain skin tone variation though we certainly can’t rule it out.

    • K. says:

      Above reply seem to confuse genetics with linguistics; Aryan refers to a family of languages; “Aryan Invasion and preference for Aryanness”? What is all with relevance to genes and races? ANI-ASI admixture has nothing to do with SLC24A5; even high-ASI races have 50% SLC24A5.

      • little spoon says:

        Aryan should properly refer to an ancient ethnic group, not only a group of languages. Originally, there was no difference between Aryan language group and Aryan ethnic group.

        “ANI-ASI admixture has nothing to do with SLC24A5; even high-ASI races have 50% SLC24A5”

        What? ANI-ASI admixture really has nothing to do with SLC24A5? Doesn’t ANI-ASI admixture have a very marked effect on complexion? Are you implying that SLC24A5 is found in consistent levels throughout south asians, regardless of ANI-ASI composition? And that means consistent levels, not just ASI high groups having more SLC24A5 than expected. Because unless that is true, ANI-ASI admixture does have something to do with SLC24A5 prevalence.

  18. Nanonymous says:

    All forms of albinism come, to various degrees, with neurological disorders. So looking at pleiotropy might tell something (and then maybe looking back at these Ethiopians.)

  19. John G says:

    There is no reason why the existence of the mutation in Ethiopia must be due to some form of direct selection. Caucasoid invaders from the North could have carried the mutation into Ethiopia.

  20. Greying Wanderer says:

    If it’s anything to do with iodine in milk then it’s IQ.

    http://www.newsmaxhealth.com/Dr-Brownstein/iodine-pregnancy-IQ-ADHD/2014/01/22/id/548448

    • Greying Wanderer says:

      This is just me wildly speculating so ton of salt etc but if it’s the above what effect did the industrial revolution have on breast feeding?

      • Greying Wanderer says:

        Again just speculating but if it was correct that would be an interesting test for the blank slate nonsense kommisars: admit IQ differences alongside a possible at least partial solution – Iodine supplements – or keep quiet to maintain the ideology?

      • The fourth doorman of the apocalypse says:

        We already know that Iodine supplements make a difference, but they are not the solution to the achievement gap in a first-world country. Only R = h^2 * S is.

  21. Greying Wanderer says:

    “We already know that Iodine supplements make a difference”

    But what percentage of the parents in the world whose children could benefit from that knowledge are included in that “we?”

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