Jerry Coyne on race: a reflection of evolution

By Razib Khan | February 29, 2012 8:53 am

After my post on the ‘race question’ I thought it would be useful to point to Jerry Coyne’s ‘Are there human races’?. The utility is that Coyne’s book Speciation strongly shaped my own perceptions. I knew the empirical reality of clustering before I read that book, but the analogy with “species concept” debates was only striking after becoming more familiar with that literature. Coyne’s post was triggered by a review of Race?: Debunking a Scientific Myth and Race and the Genetic Revolution: Science, Myth, and Culture. He terms the review tendentious, and I generally agree.

In the early 20th century Western intellectuals of all political stripes understood what biology told us about human taxonomy. In short, human races were different, and the white European race was superior on the metrics which mattered (this was even true of Left-Socialist intellectuals such as H. G. Wells and Jack London). In the early 21st century Western intellectuals of all political stripes understand what biology teaches us about human taxonomy. Human races are basically the same, and for all practical purposes identical, and equal on measures which matter (again, to Western intellectuals). As Coyne alludes to in his post these are both ideologically driven positions. One of the main reasons that I shy away from modern liberalism is a strong commitment to interchangeability and identity across all individuals and populations as a matter of fact, rather than equality as a matter of legal commitment. In a minimal government scenario the details of human variation are not of particular relevance, but if you accept the feasibility of social engineering (a term I am not using in an insulting sense, but in a descriptive one) you have to start out with a model of human nature. So this is not just an abstract issue. For whatever reason many moderns, both liberals and economic conservatives, start out with one of near identity (e.g., H. economicus in economics).

I want to highlight a few sections of Coyne’s post:

What are races?

In my own field of evolutionary biology, races of animals (also called “subspecies” or “ecotypes”) are morphologically distinguishable populations that live in allopatry (i.e. are geographically separated).  There is no firm criterion on how much morphological difference it takes to delimit a race.  Races of mice, for example, are described solely on the basis of difference in coat color, which could involve only one or two genes.

Under that criterion, are there human races?

Yes.  As we all know, there are morphologically different groups of people who live in different areas, though those differences are blurring due to recent innovations in transportation that have led to more admixture between human groups.

Why do these differences exist?

The short answer is, of course, evolution.  The groups exist because human populations have an evolutionary history, and, like different species themselves, that ancestry leads to clustering and branching, though humans have a lot of genetic interchange between the branches!

But what evolutionary forces caused the differentiation?  It’s undoubtedly a combination of natural selection (especially for the morphological traits) and genetic drift, which will both lead to the accumulation of genetic differences between isolated populations.  What I want to emphasize is that even for the morphological differences between human “races,” we have virtually no understanding of how evolution produced them.  It’s pretty likely that skin pigmentation resulted from natural selection operating differently in different places, but even there we’re not sure why (the classic story involved selection for protection against melanoma-inducing sunlight in lower latitudes, and selection for lighter pigmentation at higher latitudes to allow production of vitamin D in the skin; but this has been called into question by some workers).

As for things like differences in hair texture, eye shape, and nose shape, we have no idea….

I have no idea if reading Coyne’s earlier work influenced me, but observe that he too emphasizes that human races are a reflection of evolutionary history. Some of my interlocutors believe it is essential to have a tree-like phylogeny with no reticulation (gene flow across branches) to have a reasonable model for race, but I do not. That’s because the focus for me is evolutionary history. I want to understand evolutionary history. Taxonomy is a means to that end. It is not the end.

Coyne has a follow up post which will be of no surprise to reader of this weblog. But I do want to add a few things. 1) For pigmentation we do now understand its genomics relatively well. It seems that light skin emerged at least twice at the two ends of Eurasia, and, that it was a recent emergence (as evidence by markers of selective sweeps). 2) As for hair texture, there is some work which has shed light on this. East Asians in particular carry a variant of EDAR which gives them their distinctive thick straight hair. There has been less work on “woolly hair,” but I suspect that it will be elucidated soon (there are some candidate genes, from linkage studies and animal models). Additionally, I think it is important to note that the dark-skin-as-protection-against-skin-cancer does not make much evolutionary sense. Melanoma strikes later in one’s reproductive years. Rather, I accept that Nina Jablonski has the right of it when she argues that it protects against neural tube defects which arise because of various chemical changes which occur in one’s biochemistry due to exposure to sun. Finally, I think Coyne underestimates the power of even gene genomics using haplotype based techniques in narrowing down on very specific geographical and population origins for segments of your DNA right now. The key is not where you come from, it is how segments of your DNA relate to the full range of segments of other peoples’ DNA.

CATEGORIZED UNDER: Human Evolution
MORE ABOUT: Race
  • Darkseid

    Isn’t implying that there’s minimal difference between races like saying there’s minimal differences between dog breeds? There are genes of large effect and some genes that are basically exclusive to certain groups, etc. Cochran also points out that if the point about group variation were valid then there’d be more variation in skin color between blacks and other blacks than there would be between blacks and whites. Then there’s all the decades of athletic and intellectual differences, etc. His post seemed to be pandering more than clarifying to me.

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

    #1, he’s speaking as an evolutionary geneticist without any interest in humans. we’re a relatively recently radiated species which has Fst on the low side. so i can see why he’d say that. also: t that if the point about group variation were valid then there’d be more variation in skin color between blacks and other blacks than there would be between blacks and whites. don’t confuse a general trend with a categorical universal trend. that’s the dumb position that people use when they want to refute a statistical truth.

  • Bobby LaVesh

    Additionally, I think it is important to note that the dark-skin-as-protection-against-skin-cancer does not make much evolutionary sense. Melanoma strikes later in one’s reproductive years.

    ———————————————————-

    I’m not saying the alternative explanation given is not corret- but could the above statement be true today but less true 5,000 years ago? Recent human history has seen people avoiding the sun and being indoors for long and longer stretches of time- this could explain why we get Melanoma in later years.

    Someone with pale skin in an equitorial lattitude would surely be more likely to develop sun-related issues sooner in times pre-agriculture.

    Surely even getting a bad sun burn would place an individual at a disadvantage- it wouldn’t have to be cancer. Being sensitive to sun could make that individual seek to avoid sunlight more than his darker skinned neighbours- thus giving his less opportunity to seek food- and reproduce? It doesn’t take melanoma for it to be a disadvantage to high light skin in those areas.

  • Miguel Madeira

    A person with a very light skin can have severe skin damages if he is exposed unprotected to the sun in the Summer in southern Portugal (1 day is enough); the pain that these produce can interfere, in a “primitive” environment, with his skills at finding food, fighting, etc. Now imagine, not the Mediterranean sun, but sub-saharan african sun.

  • Darkseid

    Razib, i was using this:
    http://westhunt.wordpress.com/2012/01/26/lewontins-argument/
    post. You are saying the skin color example in the first paragraph is incorrect?

  • http://www.livinganthropologically.com/ Jason Antrosio

    With regard to the issue of skin color, the recent research summary by Nina G. Jablonski and George Chaplin, “Human skin pigmentation as an adaptation to UV radiation” (2010) is very informative: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3024016/?tool=pmcentrez

    This paper suggests that “photoprotective” and Vitamin D3 absorption explanations do not have to be mutually exclusive. “Photoprotective” skin is a cline developing near the equator, but to explain depigmentation outside the tropics, the Vitamin D3 hypothesis results in another cline. As Jablonski and Chaplin write in their abstract, and consistent with what Razib writes above: “Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection.”

  • Insightful

    East Asians in particular carry a variant of EDAR which gives them their distinctive thick straight hair.

    Roughly how old is this variant, Razib??..

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

    re: skin cancer, point taken.

    You are saying the skin color example in the first paragraph is incorrect?

    no, it’s trivially correct. my point is that as a generality one can reasonably argue that the differences are not that large (i don’t hold to this necessarily myself). but there are going to be atypical cases. e.g., SLC24A5 has an Fst ~ 10.

    Roughly how old is this variant, Razib??..

    not very. shows up as a recent sweep. so probably on the order of 10,000 years. the munda people brought it to india, so probably over than 5,000 years though.

  • http://www.isteve.blogspot Steve Sailer

    Since the 1990s, I’ve held the view that the species model is of only limited help in thinking about “race” as we read about it in the newspapers. A more productive analogy is extended families. In fact, racial groups are particular kind of extended families that are more coherent over time due to some degree of inbreeding.

  • Onur

    Steve, the extended families model can also be applied to the taxa higher than races. In fact, I think all of the current taxonomic ranks should be abandoned in favor of an extended families model (there are already promising alternatives based on extended families).

  • gcochran

    “Western intellectuals” – I have sometimes seen people try to list what a real intellectual should know. I think it might be more illuminating to list what he shouldn’t.

  • Darkseid

    R – Ok, thanks, I see what you’re saying. I usually note how a slight difference between chimps and humans can illuminate how much a slight difference can make fwiw. Not arguing, just mentioning it for anyone else who cares. Excellent post, btw.

  • juan

    An especially pale Nordic friend of mine got sun poisoning as a child when his family vacationed in Florida. It was the first time in his life he spent out in all-day bright summer sun like that. He was bed-ridden for several days after. Of course, he’s on the extreme end of paleness.

  • http://www.livinganthropologically.com/ Jason Antrosio

    On the question of skin color, the recent paper by Nina G. Jablonski and George Chaplin, “Human skin pigmentation as an adaptation to UV radiation” (2010) is very informative:

    http://www.pnas.org/content/107/suppl.2/8962.full

    It would seem that “photoprotective” explanations and Vitamin D3 absorption explanations do not have to be mutually exclusive. Jablonski and Chaplin argue for a “photoprotective” cline near the equator–however, to explain why there might be a depigmentation outside the tropics is where the Vitamin D3 hypothesis comes in, resulting in an another cline. As Jablonski and Chaplin write in their abstract–and fully consistent with what Razib writes above: “Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection”

  • http://www.scribd.com/doc/74944514/ Robert Dole

    “Some of my interlocutors believe it is essential to have a tree-like phylogeny with no reticulation (gene flow across branches) to have a reasonable model for race, but I do not.”

    What constitutes “race” (quotes not intended to sound pretentious) might depend on the evolutionary history and phenotypic significance of a particular functional gene (the latter of which might be pleiotropic, compounding the complexity). Genes already constitute haplostuff, so diversity at that scale is well defined.

    India and Brazil might be said to share a “racial affinity” at the chromosome scale because of the trichotomy of African, European (more Ys), and Asian (more mitochondria). I realize you know all this, but I mention it here as another scale at which the word “race” might be applied by people trying to use it somewhere in a rigorous context.

    Trying to pin down a genetic scale to use the word “race” is, if one assumes the most linguistically plastic view, an exercise in futility because the phenotypic effects that define it as a “social construct” (again, not being pretentious, just being rigorous) are caused by both natural selection and mate selection, each of which come at the genome in wildly different manners (and converge at the limit of viable reproduction, the hard definition of species (although possibly not the whole picture if one takes into account intraspecific patterns in viable reproduction (which seem essentially identical between races of humans))). Natural selection uses every genetic scale, and relies entirely on the final phenotype’s survivability in a given environment.

    Mate selection takes advantage of selfish genetic elements (and is, at its core, the same) in an asymmetrical manner, altering the frequency of sex chromosomes and mitochondrial lineages (differently in different human groups as well). If the genome weren’t a heterogeneous mishmash (read: small world network) of pleiotropic and epistatic effects, then race could be a globally well-defined concept at every scale. This would also, of course, mean that changes in phenotype happen at a perfectly consistent rate, instead of a rate that depends on the interactions of differently behaved macromolecules with various physical constraints (lipid membranes and such). If Y-specific stuff tends to code for more sexual dimorphism, then that cluster of genes (shared orbital world-line, if you will (at least since that swap with an X chromosome 40kya)) is gonna be defined by sex-specific selection pressures.

    People who talk about races without scoffing or laughing awkwardly often bring up dogs as an example of phenotypic variation between subspecies that is undeniable and recent. The proper liberal response is to say that recent dog selection is unnatural and due to human intervention, but that’s not the whole issue. Dogs tend to have minimal sexual dimorphism in the traits we select them for. That means that the traits that vary the most between different breeds of dogs, even if they’re also under mate selection in dogs themselves (e.g. pheromone/olfactory stuff in the MHC or similar somesuch), are under very strong pressure in both sexes equally.

    In a sense, humans “artificially” (internally) select themselves (to a degree), and this throws a bit of a wrench in the (otherwise perhaps viable) dog analogy. The MHC is under selection for diversity (in effect under negative selection for itself) at multiple scales (as I understand it, it alters behavior, immune function, olfaction, etc.), so perhaps the phenotypes that are meant to make more of the long distance connections (genetic, social, gut-microbiomic, etc.) are also genetically wired to make more varied mate/kin/citizen selections. At least in the mate-selection domain, the less racist folks tend to be the ones that are more accepting in general. If one’s racist tendencies are in part genetically determined, perhaps they’re coupled to (or derive from the effects of) one’s immune system or hard-wired ability to analyze of faces (both of which are connected to MHC-stuff).

    So if less-local reproductive behaviors are under less-local (which tends to mean less-racist) selection pressures and are represented by a particular phenotype (cluster of traits) that exists (perhaps to varying degrees) in every human group/race, then that phenotype might also be under selection pressure for most of the stuff that we care about. Local traits might have more local meaning, and indeed might turn out to have a more global use later (redheads get more sex everywhere, not just Ireland), but the traits that more phenotypically “worldly” folks select for will tend to be “worldly” themselves.

    Because of the fact that the sexes tend to have wildly different mate selection strategies (due to intrinsically different (gendered) mates), and the “worldly” (hypersocial) phenotype/tendency seems to exist in both genders, there is selection for more globally relevant traits happening in both directions. By isolating polygenic and monogenic genes into structures that control dimorphism and metabolism, respectively, natural selection (which tends to pressure metabolism) and mate selection (which, at its simplest, pressures sexually dimorphic traits) have enough overlap to give humans a large pool of traits that exist in every human niche/group of sufficient size.

    The metabolic limits set by mtDNA might be countered/checked by the Y chromosome’s ability to selectively turn off expression for other parts of the genome. If a human group exhibits too much sexual dimorphism, one sex might then be under-utilizing metabolic channels that exist in both (but are only under direct selection in one). The group-wide fitness loss might exert monogenic (global) selection pressure to counter local sex differences in metabolism utilization. Human’s matrilineal metabolic restriction might work much in the same way that propping up dictators in countries that only produce 20% of the world’s oil can still give you fantastic control of a global market (controlling the spice, if you will).

    If mitochondria are the monogenic hippie liberals who think everyone’s the same (and, to them, everyone almost is), and they control energy production, then Y chromosomes are the polygenic, palindromic (molecular masturbation?) Ayn Rands (yes, I see the irony) of the genome. If we weren’t internally selecting (not quite artificially, perhaps “recursively”) at multiple geographic scales (for traits that relate to that scale) in every human group, perhaps definitions of race that include stuff like g (instead of dermal melanin) might more readily follow an environmentally defined gradient.

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

    re: sexual dimorphism, please keep in mind whenever discussing it that it is an order of magnitude slower in terms of reaction to selection than other traits. this is warning to everyone.

  • http://www.scribd.com/doc/74944514/ Robert Dole

    “re: sexual dimorphism, please keep in mind whenever discussing it that it is an order of magnitude slower in terms of reaction to selection than other traits. this is warning to everyone.”

    Is that because androgynous folk make more babies?

    Genetic factors predisposing to homosexuality may increase mating success in heterosexuals (2008)
    “We show that psychologically masculine females and feminine men are (a) more likely to be nonheterosexual but (b), when heterosexual, have more opposite-sex sexual partners. With statistical modelling of the twin data, we show that both these relationships are partly due to pleiotropic genetic influences common to each trait. We also find a trend for heterosexuals with a nonheterosexual twin to have more opposite-sex partners than do heterosexual twin pairs. Taken together, these results suggest that genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population.”

    http://www.sciencedirect.com/science/article/pii/S1090513808000688

  • DK

    it is important to note that the dark-skin-as-protection-against-skin-cancer does not make much evolutionary sense. Melanoma strikes later in one’s reproductive years.

    Melanoma, as everything, has distribution. Part of it is firmly within reproductive years – females in particular.

    Rather, I accept that Nina Jablonski has the right of it when she argues that it protects against neural tube defects which arise because of various chemical changes which occur in one’s biochemistry due to exposure to sun.

    Never heard of it. What are these neural tube defects and what are these various chemical changes?

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

    Is that because androgynous folk make more babies?

    no. it’s basic if you try and think about evolutionary biology, instead of mindlessly citing papers.

    http://www.gnxp.com/MT2/archives/003689.html

    your comments need to be shorter. you don’t know enough to be interesting to read at such length. (this is not a comment which should elicit a response, it’s a directive)

  • DK

    Funny how one can publish a paper in PNAS about the role of folate photolysis without ever citing an evidence that local depletion of folate has appreciable consequences for its concentration in the rest of the body. And the first relevant abstract in Pubmed reads: “Serum and erythrocyte folate levels in healthy volunteers and in psoriasis patients were not influenced to any statistically significant extent after exposure to solar radiation, to single or to multiple UV treatments”.

  • http://www.scribd.com/doc/74944514/ Robert Dole

    I fucking love the internet :D

  • RafeK

    Razib I was under the impression going back to this post http://www.gnxp.com/MT2/archives/004046.html that fst divergences between human races were on the middling to high side for animal sub species and the gap between african and non africans was actually particularly large.

    Was Jason off base here or has the Data shifted over the last 6 years?

  • RafeK

    Found this interesting article which indicates human continental races have FST values that are large, similar in degree to the sub species divergence in chimps, and greater then that seen in gray wolves, lynx, or african buffalo. https://lesacreduprintemps19.files.wordpress.com/2011/06/woodley-2009-is-homo-sapiens-polytypic-human-taxonomic-diversity-and-its-implications.pdf

    I have to admit I don’t have a very deep understanding of fst or pop gen statistical methods so I am fumbling in the dark a bit here but the research I did on sub species as an undergrad always left me with the impression that continental races fit rather well into general usage of sub species for other animals.

  • Tom Bri

    May be relevant, cattle breeders many years ago observed that extremely masculine bulls produce daughters that are more feminine, will have higher milk production. So in the dairy breeds there is selection for more masculine bulls. In beef breeds there is no point in increasing milk production, so they are not selected for hyper-masculinity, but are for fast growth. Beef bulls tend to be less aggressive, less dangerous to work with than dairy bulls.

    Be interesting to see if there is any correlation between father masculinity and daughter femininity in humans.

  • Barbara

    Re: human skin pigmentation and sunlight. Maybe there’s a third player — plants. In a number of plant species, eating the plant or even touching the sap can cause photosensitization. If the pale-skinned individual is exposed to bright sunlight after interacting with the plant, chemicals from the plant block capillaries. This can result in unusually severe sunburn or (in sheep) in loss of ears, lips, etc. The results can be fatal, sometimes from starvation. Hunter/gatherer humans must have been exposed to these plants often, and at young ages. This could produce selection for dark skin, especially where sun is bright.

  • Barbara

    Re: selection of dairy bulls. Breeders did not select for “masculine” bulls but for bulls whose mothers, sisters, etc., produced more milk than most dairy cows. The dangerous aggression seen in modern dairy bulls was a by-product of the selection, not the object of it, as implied above.

  • http://www.livinganthropologically.com/ Jason Antrosio

    In a recent comment to my blog-post on these issues, Henry Harpending suggested taking a look at the work of Guido Barbujani. As Harpending enjoined: “Why chatter about something when one can come up with a ruler and measure it?”

    Barbujani’s measurements are indeed quite instructive–I recommend his 2010 paper (co-authored with Vincenza Colonna) as a careful overview relevant to both the post from Jerry Coyne and some of the comments in this stream. Please see Human genome diversity: frequently asked questions, and I’m grateful to Harpending for a very helpful resource.

    Interestingly, both Harpending and Coyne use the metaphor of human genetic diversity as a “lumpy pudding.” I’m not sure if this is an old trope for geneticists or a new trend, but here is Coyne on the issue:

    “As I said, this doesn’t show that there are discrete ‘races’ in Europe, and I don’t think there are obviously discrete ‘races’ anywhere these days, though there is large-scale genetic differentiation among worldwide population suggesting that such races once existed as relatively discrete and geographically isolated populations. The discreteness that once existed, or so I think, is now blurring out as transportation and migration are beginning to mix the discrete groups into not a melting pot, but sort of a lumpy pudding of humanity.”

    Coyne is not entirely incorrect, but his notion that discreteness once existed but is only “now blurring” with what he termed in the previous post “recent innovations in transportation” is odd–is he talking about airplanes of the last 50 years, the railroads of the last 150 years, or the transoceanic voyages of the last 500?

    Coyne’s idea of ancient discreteness only recently turned into lumpy pudding is unsupported—not by Barbujani and Colonna’s 2010 review, not by the 2009 material I’ve been referencing from “Race Reconciled”, not from what I read on Dienekes blog, not from what I get from John Hawks: admixture is ancient and normal, not recent and exceptional.

    For my more elaborated response to Henry Harpending, please see Race redux: What are people “tilting against”?

  • Martin

    Hey Razib, one of the most interesting aspect of that article was in the comments section, somebody pointed out a seemingly serious mathematical flaw in the entire Fst = human biodiversity issue, and the ‘more variation within groups than between’ argument.

    ” when within-group variation is high, the between-group variation is ALWAYS small compared to the within-group variation, and the ratio of between-group variation to total variation approaches zero, even if the groups share no genes whatsoever”

    ie, the only way to meaningfully do this, would be by comparisons of Absolute differences. (he said that it was a better indicator of true evolutionary divergence for fruitflies than Fst )

    Can you comment on this, or perhaps write a blog entry, would love to hear your opinion!

  • Ian

    When I was younger, I thought of human races as archetypes, and the variation between them a product of mixing. I blame it on the fact that I read Coon when I was about 14. Still, as a (half)Indian, it’s hard to see reconcile the reality of a billion people in the subcontinent with models that try to classify people into 3-5 races. As I learned more biology, I came to the conclusion that human variation was clinal, and race was really an artefact of where you chose to sample along the continuum…as a plant ecologist, I think about things like that a lot. (I’m also somewhat skeptical of ecozones.)

    Thanks to a number of convergent strands (of which Razib’s blogging has been a key element), I have come to a rather different conclusion. Race, in my opinion, is more a feature of agriculture than evolution.

    Consider two possible models of race: Model 1, in which sharp distinctions existed before the Neolithic, and have been maintained and enhanced as certain groups adopted agriculture and displaced their hunter-gatherer neighbours; and Model 2, in which variation was clinal prior to the Neolithic, but that the immense demographic expansion of certain groups expanded THEIR specific points on the continuum, and brought them into contact (or nearly into contact) with other expansionist agriculturalists.

    To me, the Model 2 seems more plausible than Model 1. Is that an argument against race? No, but it does suggest that races shouldn’t really be seen as “locally adapted optima” and rather, should be seen more as transient phenomena produced by historic contingency. Whether this means that race is “real” or not is, to me, a little beside the point. But I’m not convinced by Coyne’s argument that these differences represent the “accumulation of genetic differences between isolated populations”.

  • Eddy

    @Robert Dole

    Regarding hardwired racism.. Hyenas that have never encountered Lions will become aggressive around items that smell like lions. I know this is an extreme example but I think you have a point.

    Regarding “g” as a measure of race. Even the most g-loaded tests can be studied for. Engineers are often ‘trained’ to be better at these kind of ‘creative logistic’, ‘puzzle’ problems. Children exposed to puzzles early when intelligence hasn’t yet crystallized also perform much better on these tests as adults. If you’ve ever seen the questions on an IQ tests you’d know that the high heritability estimates from certain studies to be questionable at best (Examples if requested). Even assuming high (60% + etc.) heritability the Flynn effect shows that populations cognitive levels can go up 2 standard deviations in 2-3 generations.

    Also there is increasing evidence for multiple forms of intelligence. For example, hyenas are better ‘group problem solvers’ than even Chimpanzees who outperform them in every other cognitive field by far.

    Regarding dog breeds as examples of race.. Correct me if I’m wrong but isn’t the separation among breeds of dog roughly 3-5x greater than the separation of human clusters?

    To me, race seems determined by visibly observable traits and by culture more than anything.

  • Tom Bri

    Hi Barbara, Sorry if I implied that aggression was a trait sought by dairy breeders. As you said, it is simply a side effect, undesired.

    As for photo-sensitization, chamomile is one culprit. I had a fair-skinned friend who liked chamomile. We were living in the sub-tropics. I suggested he quit drinking it after he complained about getting sensitive to the sun.

  • DK

    Correct me if I’m wrong but isn’t the separation among breeds of dog roughly 3-5x greater than the separation of human clusters?

    You are wrong. It’s only ~ 2X ( https://www.princeton.edu/genomics/kruglyak/publication/PDF/2004_Parker_Genetic.pdf ) and, as could be expected, it’s inflated by relatively few sites that show great degree of between-breeds variation ( http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1002316 ).

  • Barbara

    Interesting that chamomile would cause photosensitization. I know two people who suffered serious skin burns (scarring in one case) from contact with sap of parsnips (Pastinaca) and cow parsnip (Heracleum). Eating St. John’s wort (Hypericum) and vegetation of buckwheat (Fagopyrum) can cause it.

    In addition, many plants can cause liver damage that prevents the liver from breaking down phylloerythrin (produced by breakdown of chlorophyll), thus causing photosensitization.

    Relevance to selection for human skin pigmentation might be suggested by this description of symptoms in non-human mammals: Both light and the presence of a reactant substance in the peripheral circulation are required. Therefore, the reaction will occur only in areas of unpigmented or lightly pigmented skin which is not covered by a dense light-screening coat of hair. . . . white sheep are affect particularly about the head, and cattle on white or unpigmented areas of the skin . . . Black-skinned animals are resistant, but may not prove immune to massive exposures. (Kingsbury1964, p. 35)

    Although humans would probably tend to avoid eating plants that cause photosensitization, choices would be limited during times of famine. And of course it takes a while for a population to develop an understanding of which plants are toxic, as they enter new ecoregions.

  • Sandgroper

    Barbara: “And of course it takes a while for a population to develop an understanding of which plants are toxic, as they enter new ecoregions.”

    Australian Aboriginal people ate some plants native only to Australia that were very toxic unless subjected to quite lengthy and complex multi-stage processing to leach out the toxins.

    My question is – how the hell did they find out what they needed to do to the plants to render them non-toxic?

    I have this sort of comical mental model of the women using disposable male ‘test subjects’ while they experimented, but that’s clearly not the answer.

  • Justin Giancola

    ^Okinawans did the same. And cashews, found in Indonesia I believe?, are originally toxic unless treated. Seems you guys in that part of the world are good at that.

    The cashews actually burn your skin! – even more on point!

  • Sandgroper

    Yep, workers shelling cashews need to wear protective gloves, due to the anarcardic acid in the shell. I’ve been to a cashew ‘factory’ in southern Thailand where they were doing exactly that.

  • Eddy

    @DK

    Interesting. So that would mean that the average FST between dog breeds would be around .25 – .3 (Roughly the distance between Papuans and/or Melanesians and Africans)

    Strange that Papuans and Africans are the most genetically distant (unless I’m again mistaken) but could pretty much pass for each other in many cases.

  • LongMa

    I”m watching a special right now on Dr. Nina Jablonski and her belief that folate deficiency, which she claims is the leading factor in determining how skin color developed in humans.

  • Sandgroper

    I don’t believe I would ever mistake a Papuan for an African.

  • Justin Giancola

    39. point us to it?

    40. Sandgroper, all you _insert people_ look the same from the eyes of the other, duh! What if they were both from Guinea! ;p

  • Barbara

    Sandgroper: “how the hell did they find out what they needed to do to the plants to render them non-toxic?”

    Yes — I’m amazed that people figured out the complex, multi-step, often lengthy methods needed to detoxify some plants.

  • Sandgroper

    It suggests a sophistication of thought and concepts that might not be expected. I guess they could have experimented with very small quantities of new/unknown plants, which is what you would be inclined to do, right? But even so, there had to be the chain of thought “Hmmm, that made me sick, but it’s otherwise pretty tasty – I need to process it somehow to get rid of whatever is in it that is doing that.” And then to figure out the multi-step process. That’s what really boggles me. But then Aboriginal people allegedly had a pharmacopoeia of thousands of plants (only partly documented), so figuring out how to detoxify a potential food source would probably have been relatively simple for them.

    Justin, that Spanish guy had to have been as dumb as sh*t. In real life, Papuans are some of the most distinctive people I have seen.

    I could get a bunch of Torres Strait Islanders and Aborigines from northern Queensland and mix them up, and I’m willing to bet you would have no difficulty in separating them into two correct groups, just on physical appearance.

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Gene Expression

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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