Gene Expression

Why phenotypic races may not disappear

i-21a95157fceeebf3d17b16e562a0130b-twinspic.jpgIn response to my post Mixed-race but homogeneous appearance? several individuals mooted the possibility that admixture may result in the vanishing of race as a social construct. Actually, I don’t think this is the true. To the left is a photo from my post Can you tell if you’re black or white? where I explored the genetics of a case where two black-white biracial parents produced fraternal twin daughters of disparate appearance. While one sister seemed to favor her African ancestors in look, another sister seemed to resemble her European forebears. Across the full sample space of their genome it seems likely that both these girls are about half European and half African in ancestry, but on the finite loci which are salient in the production of the features which we use to code for “races” they most certainly favor one ancestral group over the other. The basic point is that a population, and individuals, can exhibit great admixture and yet still realize the full phenotypic range of the ancestral types. This is because genetics is not blending, admixture will not result in a homogenization toward a mean unbounded by a distribution characterized by variance.

i-9a410d573150d46f2dfaf6aba8c351ef-mixedfigures.jpgBut we don’t need to stick to theory or projection from sensationalized pedigrees. There is a “natural experiment,” so to speak, and that is Latin America. In particular, there are two papers out of a Brazilian group which are relevant to the point I’m trying to make, Color and genomic ancestry in Brazilians & Color and genomic ancestry in Brazilians: a study with forensic microsatellites. To the left I’ve mashed up two figures which illustrate the most important result, and have added some text since the resolution is wanting in clarity. Here is the group’s general conclusion: ancestrally informative markers tend to suggest that individuals who identify with the three broad physical groupings, white, black and mixed, exhibit a great deal less separation in terms of the variation of total genome content then one might infer from appearance. Both papers are open access, you can check to see if their methods are up to snuff. The figures show pretty clearly that there is a great deal of intersection across the phenotypic races. Granted, a group which is avowedly mixed-race would naturally overlap the ancestral clusters, but do note that the black and white groups also overlap quite a bit, though the extent of overlap exhibits the patter one would expect. The authors placed next to the Brazilian clusters controls for European and African ancestry, which show that these clusters much more closely match our expectation that physical appearance should track ancestry. Whenever I post on this topic I do get very skeptical Brazilian readers, and I don’t dismiss objections as to the representativeness of the sample, but these studies are what I’ve found so far. I would not be surprised to find that on the national level the whites of the far south of Brazil are overwhelmingly European, for example. Additionally, someone who is “white” in Brazil may exhibit features which mark them of some African ancestry in other contexts. That being said, I am willing to bet that assortative mating driven by social selection has resulted in the reemergence of phenotypic races from a admixed population over several generations across large swaths of Brazil.

In plain English, imagine a scenario where the “white” twin above marries another “white” twin, and the “black” twin marries another “black” twin. Though the cousins produced by these pairings will all be about 1/2 African and 1/2 European in ancestry, in physical appearance they will resemble two distinct races. Though their genetic distance using ancestrally informative markers would place them between their African and European ancestors, the “white” cousins would no doubt be the beneficiaries of positive discrimination and the “black” ones negative discrimination. And that, I believe, is the key as to why the assortative mating occurred in the first place, in much of Latin America a great deal of physical variation exists within families and there is a distinct preference for the offspring with “good features,” invariably European features. These genealogically mixed-race individuals who are phenotypically white would naturally tend to solidify their lucky draw by finding a partner with the same qualities and so pass on to their children the benefits of being white.

There is the idea in the minds of some that interracial relations in the most intimate sense will banish racism or racial consciousness. To me that seems unlikely, though Latin American nations do not exhibit the sort of racism based on ancestry traditional in the United States, they do retain a marked preference for those who wear a European face, no matter what their ancestry might be. The reality of multiracial origins certainly softens the hard edge of bigotry, but it also seems to encourage a complacency as to blatant phenotypic biases. Selection is a powerful force and it can reshape human variation rather quickly given the appropriate environmental impetus. The race problem will not vanish through the fiat of genetics, rather, the social context can have a controlling effect upon the correlation of characters and their clusters within the population so as to reflect the values which that society holds up.

Comments

  1. #1 Flip
    December 21, 2007

    Steve Sailer has written about assortative mating in Mexico whereby the upper class becomes more European over the generations.

  2. #2 toto
    December 21, 2007

    Cases like this may indicate that the total number of genes that affect outward “racial” appearance is small, otherwise you wouldn’t expect such clear-cut separation to occur spontaneously out of random fluctuations. Score one for Lewontin.

    The question is: how effective could this assortive mating be in enforcing the separation of the population into distinct clusters, in terms of “outward racial appearance” genes? Well, another case of wide variation in skin colour within families, and strong preference for “whiteness”, is South Asia. The fact is that within-family variation is still strong there, after presumably millenia of fair-skin preference and assortive mating.

    (I have actually heard a female, Lahori friend of mine explain to me that South Asians make an explicit distinction between “colour beauty” (proportional to paleness) and “features beauty” (attractiveness of facial features), with the former being more valued than the latter…)

  3. #3 Dylab
    December 21, 2007

    Could you link to a larger version of the picture you posted. It is a little too small to read as it is now.

  4. #4 Caledonian
    December 21, 2007

    F2 cycles are always the most unpredictable. With repeated interbreeding, multiple-gene traits will tend to assume a ‘continuous’ distribution.

  5. #5 Eric Dennis
    December 21, 2007

    Interesting post. I wonder, though, about the stability of this social preference for whiteness. More affluent societies, marked by a large middle class, seem to be favoring a darker skin tone, indicative of racial mixture. The popularity of tanning seems related to this. Such a preference would obviously be anti-assortive and would tend to bring about homogeneity.

  6. #6 razib
    December 21, 2007

    Cases like this may indicate that the total number of genes that affect outward “racial” appearance is small, otherwise you wouldn’t expect such clear-cut separation to occur spontaneously out of random fluctuations. Score one for Lewontin.

    why? lewontin made assertions about Fst, what does this have to do with that?

    The question is: how effective could this assortive mating be in enforcing the separation of the population into distinct clusters, in terms of “outward racial appearance” genes? Well, another case of wide variation in skin colour within families, and strong preference for “whiteness”, is South Asia. The fact is that within-family variation is still strong there, after presumably millenia of fair-skin preference and assortive mating.

    you’d have to look at the parameters, selection vs. gene flow, etc. i would assert that these preferences weren’t really that relevant to the typical peasant across much of the world.

    (I have actually heard a female, Lahori friend of mine explain to me that South Asians make an explicit distinction between “colour beauty” (proportional to paleness) and “features beauty” (attractiveness of facial features), with the former being more valued than the latter…)

    this sounds about true. a southern european look is idealized (they wouldn’t say it was southern european, this predates europeans, and probably is rooted AT LEAST in the muslim period). you see this in the black american community. some dark skinned women complain that a woman can be fat, ugly or whatever, as long as she is light skinned.

    F2 cycles are always the most unpredictable. With repeated interbreeding, multiple-gene traits will tend to assume a ‘continuous’ distribution.

    with random mating the distribution will be about normal. not if there is is assortative mating it may become multi-modal.

  7. #7 toto
    December 21, 2007

    More affluent societies, marked by a large middle class, seem to be favoring a darker skin tone, indicative of racial mixture. The popularity of tanning seems related to this.

    Well, the popularity of tanning is a recent, Western phenomenon. First, AFAIK paler skins are preferred in Asia (both “brown” and “yellow”) and in the Americas – I don’t know about Africa. Second, even in Europe, until the 19th century whiteness of skin was a desirable property (at least for women.) Dark skin was directly associated with the lower classes, since they were the one staying outside (to work the fields). It only changed when tan became associated with high social status (“look, I can afford espensive holidays in sunny locations!”)

    Or at least that’s the spin my history teachers put on it.

  8. #8 Eric Dennis
    December 21, 2007

    toto, Yes I agree about the history of fairness being preferred since forever. But it appears a basic shift in that preference is taking place right now (say last ~30yrs) in affluent societies, and long-term cultural momentum seems to be behind the shift.

  9. #9 agnostic
    December 21, 2007

    Yeah, that should read “score one for Orr,” i.e., the person who says that adaptive evolution takes only a few steps to reach the peak.

    Re: tanning — that won’t affect genetics at all, since the trait is easily faked by suntanning. Moreover, *if* the preference is due to class exclusivity, then it should be getting less, not more, popular these days. After all, tanning salons are all over the place now and many are not expensive at all.

    So, the fake tan is itself now easily fakeable.

  10. #10 ewr
    December 21, 2007

    ED,

    If a skin tone occurs among tanned whites, then clearly it is not “indicative of racial mixture”.

    To the extent a tanned look is popular among whites, it is most likely due to the suggestion of outdoor activity and associated leisure and athleticism. No such associations would exist if a “permanently tanned” look were the ideal.

    Additionally, some women end up tanning for psychological reasons that have nothing to do with appearance (i.e., tanning produces changes in brain chemistry which are addictive).

    If you’re going to make assertions about “basic shifts in preferences” with “long-term cultural momentum” behind them, how about offering some evidence in the form of, e.g., survey data or articles in psychology journals.

    (By the way, if you have in mind the rise of mixed-race actresses like Halle Berry, these actually tend to prove the opposite of your point, since they’re standing in for blacks.)

  11. #11 ewr
    December 21, 2007

    Note: one of these studies uses 10 “classical” markers for ascertaining ancestry; the other uses 12 forensic microsatellites. Use more/better genetic markers and more and better-defined phenotypic markers and you’ll see less overlap.

  12. #12 ewr
    December 21, 2007

    Correction: it’s 10 actual DNA markers in the first study. The point stands.

  13. #13 razib
    December 21, 2007

    Use more/better genetic markers and more and better-defined phenotypic markers and you’ll see less overlap.

    why? are you saying people were misclassified? and what markers are you thinking of? i assume you know since you’re suggesting them. in any case, of course you’ll see less overlap as you increase the number of markers. but you hit diminishing returns. 12 markers is a relatively small number, but do note that note white and african populations were distinguished pretty easily with little overlap (after all, you only need 1 marker like SLC24A5 or duffy to distinguish someone of pure african vs. european ancestry). i think phenotypic markers is probably the better way to ascertain admixture, rather than assuming that there’s less admixture then these data suggest for these classes.

    (assman, don’t offer what characteristics you’d look for, i think we know, OK?)

  14. #14 ewr
    December 21, 2007

    are you saying people were misclassified?

    Look at the classification system they use. There appears to be plenty of room for subjectivity. And even if cutoffs are precisely defined, it not clear to me that “whites” as defined in the paper necessarily bear much resemblance to Europeans. Someone with black eyes, black frizzy hair (as long as it can be called “wavy” and not “curly”), “median” lips, and “prominent or upturned” nasal tip (appearance of the rest of the nose is unimportant) is white, according to the paper’s definition.

    A likely confounding factor in all of this is Amerindian admixture, which could potentially move an admixed individual in the “white” (as defined here) direction phenotypically, while moving them genetically away from the Portuguese.

    and what markers are you thinking of? i assume you know since you’re suggesting them.

    Whichever and however many markers as are necessary to get the statistical resolution necessary to prove what they’re trying to prove. Amerindian admixture must be taken into account, as well.

    12 markers is a relatively small number, but do note that know white and african populations were distinguished pretty easily with know overlap.

    They may be able to discriminate accurately between 100% African and 100% European with 12 STRs. What about 75% European and 75% African?

    Incidentally, forensic STRs are specifically chosen to maximize variability within populations. In general, they are not ideal for assessing admixture.

  15. #15 razib
    December 21, 2007

    ewr, your points are taken. frankly, i assume that this study overplays the hand a bit (as i said, i think there are whites in southern brazil of more recent immigrant streams that are likely not very admixed at all). that being said, i also assume that it is indicative of assortative mating, even if there are the confounding factors you note the intersection seems too great. i believe TV globo did a story on afro-brazilians (with photos) using the stuff that ancestry by dna sells and it did come up with a rather high proportion of european ancestry for many of these individuals (e.g., very dark-skinned individuals with no white facial features turning up 25% european in multiple cases).

  16. #16 ewr
    December 21, 2007

    Amerindian admixture . . . could potentially move an admixed individual in the “white” (as defined here) direction phenotypically, while moving them genetically away from the Portuguese.

    Looking at the study more closely, the authors actually claim Amerindians are in the European range on their “African ancestry index”. This is still a major confounding factor, and may contribute to some of the overlap of the “black” and “mixed” group with the “white” group.

  17. #17 ewr
    December 21, 2007

    i believe TV globo did a story on afro-brazilians (with photos) using the stuff that ancestry by dna sells

    If I’m thinking of the same program (I haven’t watched it), I thought the tests were done by a lab in Brazil. Anyway, tests of this sort should always give information on statistical certainty. When they don’t, I can’t get too excited about them.

  18. #18 Eric Dennis
    December 23, 2007

    ewr, I don’t have any statistical information for you, only some simple, but I think relevant, observations on social trends. Indication of extra leisure time and athleticism is certainly a component of the modern preference for tanned skin, but I think there is an independent component: the ascendancy of black and hispanic popular culture in America and Europe and the consequent preference for darker skin. This seems to represent a reversal in some age-old tendencies in the West.

  19. #19 kozmetik
    December 23, 2007

    one of these studies uses 10 “classical” markers for ascertaining ancestry; the other uses 12 forensic microsatellites. Use more/better genetic markers and more and better-defined phenotypic markers and you’ll see less overlap.

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