Gene Expression

A year ago, Armand Leroi, the author of Mutants, wrote:

We don’t know what the differences are between white skin and black skin, European skin versus African skin. What I mean is we don’t know what the genetic basis of that is. This is actually amazing. I mean, here’s a trait, trivial as it may be, about which wars have been fought, which is one of the great fault lines in society, around which people construct their identities as nothing else. And yet we haven’t the foggiest idea what the genetic basis of this is. It’s amazing.

Wonder no more Armand! Some have said we are in the golden age of skin color genetics. Nearly 40 years ago quantitative trait loci analysis suggested that 4-5 genes control the variation in skin color which distinguishes Africans from Europeans. And now, new work is pin pointing exactly what those genes of large effect might be. Two recent papers elucidate the underlying genomic architecture which results in human skin color variation, and the general conclusion seems to be that light skin in northern Eurasia is a derived trait which emerged independently in places like East Asia and Europe.* Within a few years a quick genomic sequence might be able to determine the expectation and variance of skin colors in the case of interracial couples.

* Dark skin seems to itself be a derived trait, but far deeper in our evolutionary history, dating to the time when hominids lost their fur.

Comments

  1. #1 Jeffery Keown
    September 25, 2006

    It’s amazing. You say it as a matter of fact, but the Xtian websites will pick it up and cry racism. They’ll claim that you said “white” humans are more evolved than darker humans. I can hardly wait to deliver the verbal smackdown when it happens.

  2. #2 razib
    September 25, 2006

    They’ll claim that you said “white” humans are more evolved than darker humans.

    well…life is a circle. our lineage started out “white,” was evolved toward darkness with loss of fur, and then lost that darkness when it was not longer necessary (there is still debate whether that loss was relaxed selection or positive selection, though i think the preponderance of the evidence on most loci point to the latter).

  3. #3 Agnostic
    September 25, 2006

    I wish I were browner so I could wear yellow…

    All I know from personal experience is that in the Japanese-French half of my family, there’s more variance than you’d expect on purely additive effects. That is, my Japanese grandmother is pretty pale, and the French side isn’t swarthy Mediterranean French but light northern. Yet two of their four kids are darker than the Japanese mean… not brown… somewhere between the mean for Japan and Thailand, I’d say.

    One of these darker siblings married a northern Euro woman, and while one of their kids looks white, the other is also dark-for-Japanese like her father. The other darkish aunt married a northern Euro guy, though their kid doesn’t look darkish at all. A whitish uncle married a Japanese woman, and their kid looks like a typical Japanese girl. My whitish dad’s kids, including me, look white (though my pallor has a Japanese hue to it — not like the Scotch-Irish pallor that my mom’s side has).

  4. #4 Autonomous Chimp
    September 25, 2006

    What could the selective pressures for freckles be? Or is that perhaps an example of allopatric speciation?

  5. #5 razib
    September 25, 2006

    All I know from personal experience is that in the Japanese-French half of my family, there’s more variance than you’d expect on purely additive effects.

    the 4-5 is salient for large differences. within population differences will be effected by a larger number of loci as the variance is necessarily smaller. the range of color between japanese and french is relatively small, so the various non-additive small effects could be relevant.

    What could the selective pressures for freckles be? Or is that perhaps an example of allopatric speciation?

    redheads are major league loss of function (they generally can’t even tan). i don’t know what selection pressures could be, but we know that other phenotypic effects are non-trivial (greater pain sensitivity), so it could be pleiotropy. honestly, i don’t know if redheads quality fully as “normal human variation.”

  6. #6 Rikurzhen
    September 25, 2006

    What could the selective pressures for freckles be?

    sexiness

  7. #7 razib
    September 25, 2006

    rik, people should put their biases on the table before offering an opinion….

  8. #8 Theresa
    September 25, 2006

    What could the selective pressures for freckles be?

    sexiness

    Absolutely! ;)

  9. #9 G Barnett
    September 25, 2006

    Suddenly I’m reminded of the Arthur C. Clarke short story in which aliens reveal they’re an offshoot of humanity that left earth long ago, and are returning with a cure for “whiteness.”

    Can’t recall the title off-hand, tho….

  10. #10 Ross
    September 25, 2006

    {aliens reveal they’re an offshoot of humanity that left earth long ago, and are returning with a cure for “whiteness.”}

    Sounds like the Nation of Islam’s formal doctrine.

  11. #11 gbruno
    September 25, 2006

    I met a young girl in Luzon, Philippines, Mother a Philippina, Father’s surname from Scotland (same as mine, Bruno is not my fathers surname), She has very pale blue eyes and pale blonde hair, seems that Norse/Viking hair/eyes genes have dominated the Philippine genes. My father had grey eyes & brown hair, not so Viking.
    http://static.flickr.com/85/248020533_6319272a7b.jpg?v=0

  12. #12 Rudy Aunk
    September 26, 2006

    Hetep and Respect Good Spirits

    Questions like this come up (unanswered)because of Cultural illiteracy. Science has long known the biological bases for Blackness (including skin color) it is the body’s capacity to produce melanin.

    If science can not yet identify the genetic markers for melanin production it is because they do not completely understand how melanin works.

    Discussions about Blackness (including skin color) without including melanin, are created out of Cultural Illiteracy or as and act of Cultural terrorism.

    For more information on the basis of Blackness hit this link and tell me what you think.

    http://lulu.com/aunk

  13. #13 pconroy
    September 26, 2006

    Re: Freckles…

    I think they evolved – much like a leopards spots – as camoflague in a wooded environment for our hunter ancestors?!

  14. #14 somnilista, FCD
    September 26, 2006

    Skin deep, why I’m brown and you wish you were

    I wish I were brown so that I couldn’t be racist ;]

  15. #15 Agnostic
    September 26, 2006

    Re: target of freckles — if it’s sensitivity to pain, that also correlates with being introverted, which makes one less tolerant of all sorts of stimuli (loud noises, lemon juice, distractions while working, etc.). I don’t know post-agricultural Irish history, but there may have been a social or ecological pressure to become less gregarious. The most reliable data on national levels of personality traits don’t have data for Ireland by itself, but I think it’s safe to say that when not inebriated (joke!), the Irish are on avg less sociable & fast-paced than other Euro groups.

    Anyone who knows history care to hazard a guess?

  16. #16 pconroy
    September 27, 2006

    Agnostic,

    I think of the Irish as the more sociable people in Northern Europe, and generally appreciate and indulge in lots of quick witted joking around and word play of all sorts. I also think that they tend to be stoical and pragmatic when faced with adversity. They are also probably one of the most macho Northern European countries, particularly when juxtaposed against the Scandanavians, but not against the Scottish. I see them as less disciplined than some other European countries, but more innovative and less fearful of change…
    That’s my 2 cents – but hey, I’m probably biased and subjective about my own?!

    One would need a cross-cultural study to verify or refute these kinds of things…

  17. #17 Autonomous Chimp
    September 27, 2006

    Actually, I think it is sexiness. Everything I’ve found online points to sexual selection for freckles and red hair among the Ancient Hibernians.