Is Girls’ Generation the outcome of the Pleistocene mind?

By Razib Khan | February 19, 2013 1:37 am

There’s an excellent paper up at Cell right now, Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant. It synthesizes genomics, computational modeling, as well as the effective execution of mouse models to explore non-pathological phenotypic variation in humans. It was likely due the last element that this paper, which pushes the boundary on human evolutionary genomics, found its way to Cell (and the “impact factor” of course).

The focus here is on EDAR, a locus you may have heard of before. By fiddling with the EDAR locus researchers had earlier created “Asian mice.” More specifically, mice which exhibit a set of phenotypes which are known to distinguish East Asians from other populations, specifically around hair form and skin gland development. More generally EDAR is implicated in development of ectodermal tissues. That’s a very broad purview, so it isn’t surprising that modifying this locus results in a host of phenotypic changes. The figure above illustrates the modern distribution of the mutation which is found in East Asians in HGDP populations.

One thing to note is that the derived East Asian form of EDAR is found in Amerindian populations which certainly diverged from East Asians > 10,000 years before the present (more likely 15-20,000 years before the present). The two populations in West Eurasia where you find the derived East Asian EDAR variant are Hazaras and Uyghurs, both likely the products of recent admixture between East and West Eurasian populations. In Melanesia the EDAR frequency is correlated with Austronesian admixture. Not on the map, but also known, is that the Munda (Austro-Asiatic) tribal populations of South Asia also have low, but non-trivial, frequencies of East Asian EDAR. In this they are exceptional among South Asian groups without recent East Asian admixture. This lends credence to the idea that the Munda are descendants in part of Austro-Asiatic peoples intrusive from Southeast Asia, where most Austro-Asiatic languages are present.

And yet one thing that jumps out at me is that there is no East Asian EDAR in European populations, even in Russians. I am a bit confused by this result, because of the possibility of Siberian-affiliated population admixture with Europeans within the last 10,000 years, as adduced by several researchers (this is not an obscure result, it manifests in TreeMix repeatedly). The second figure shows the inferred region from which the East Asian EDAR haplotype expanded over the past 30,000 years. The authors utilized millions of forward simulations with a host of parameters to model the expansion of EDAR, so that it fit the distribution pattern that is realized (see the supplements here for the parmeters). To make a long story short they infer that there was one mutation on the order of ~30,000 years before the present, and that it swept up in frequency driven by selection coefficients on the order of ~0.10 (10% increase relative fitness, which is incredibly powerful!). This is on the extreme end of selective sweeps, and likely of the same class as the haplotype blocks which characterize SLC24A5 and LCT (the block is shorter, though that makes sense because of the deeper time depth). Again, I am perplexed why such an ancient allele, which is found in Amerindians, or Munda populations, is absent in Europeans who have putative East Eurasian admixture. The whole does not cohere for me. There is a weak point in one or more of my assumptions.

Then there’s the section on the mouse model. To me this aspect was ingenious, though I’m not particularly able to assess it on its technicalities. The earlier usage of mouse models to test the effects of mutations on EDAR was in the context of coarse copy number changes which resulted in massive dosage changes of protein. The phenotypic outcomes were rather extreme in that case. Here they used a “knockin” model where they recreated the specific EDAR point mutation. Instead of extreme phenotypes they found that the mice were much more normal in their range of traits, though the hair form shifts were well aligned with what occurred in humans. Additionally there were some changes in the number of eccrine glands, with a larger number in the derived East Asian EDAR carriers (with additive effect). Finally they noticed that there were differences in mammary gland pad area and branching. None of this is that surprising, EDAR is a significant regulatory gene which shapes the peripheries and exterior of an organism.

To double check the human relevance of what they found in the mouse model they performed a genome-wide association in a large cohort of Han Chinese. The correlations of particular traits were in the directions that they expected; those individuals with East Asian EDAR variants had thicker hair, shovel-shaped incisors, and a greater density of eccrine glands. It is perhaps important to note that the frequency of the derived variant is so high in Han populations that they didn’t have enough homozygote ancestral genotypes to perform statistics, so their comparisons involved heterozygotes with the derived mutant and also a copy of the ancestral state. This is like SLC24A5 in Europeans, where it is difficult to find individuals of European heritage who have double copies of the non-European modal variant.

Let’s review all the awesome things they did in this study. They dug deeply into the evolutionary genomics of the region around the EDAR, concluding that this haplotype was driven up in frequency from on ancestral variant ~30,000 years ago in a hard selective sweep. And a sweep of notable strength in terms of selection coefficient. This may be one of the largest effect targets of natural selection in the genome of non-Africans over the past 50,000 years. Second, they used a humanized mouse model to explore the range of phenotypes correlated with this mutational change in East Asians. So you have a strong selection coefficient on a locus, and, a range of traits associated with changes on that locus. Third, they confirmed the correlation between the traits and the mutation in humans, despite there being prior research in this area (i.e., they reproduced). This is all great science, and shows the power of collaboration between the groups.

Much of the elegance and power of the paper applies to the discussion section as well, but to be frank this is where things start falling apart for me. You can get a sense of it in The New York Times piece, East Asian Physical Traits Linked to 35,000-Year-Old Mutation. The headline here points to a legitimately important inference from this line of research, many salient physical characteristics of the human races seem to be due to strong selection events at a few loci. In addition to EDAR I’m thinking of the pigmentation loci, such as SLC24A5. I wouldn’t be surprised if there was something similar for the epicanthic fold. If it is visible, and defines between populations differences, it is generally not genomically trivial. There’s usually a story underneath that difference.

In the broad scale of human natural history the problem that arises for me is that we have traits, we have genes under selection, but we have very weak stories to explain the mechanism and context of natural selection. Here there is a strong contrast with the loci around lactase persistence and malaria resistance. In those situations the causal mechanism for the selection seems relatively clear. Critics of evolutionary psychology are wont to accuse the field of ‘Just So’ storytelling, but the same problem crops up in the more intellectually insulated domain of evolutionary genomics (in part because the field is very new, and also mathematically and computationally abstruse). To illustrate what I’m talking about I’m going to quote from the discussion of the above paper:

A high density of eccrine glands is a key hominin adaptation that enables efficient evapo-traspiration during vigorous activities such as long-distance walking and running (Carrier et al., 1984; Bramble and Lieberman, 2004). An increased density of eccrine glands in 370A carriers might have been advantageous for East Asian hunter-gatherers during warm and humid seasons, which hinder evapo-transpiration.

Geological records indicate that China was relatively warm and humid between 40,000 and 32,000 years ago, but between32,000 and 15,000 years ago the climate became cooler and drier before warming again at the onset of the Holocene (Wang et al., 2001; Yuan et al., 2004). Throughout this time period, however, China may have remained relatively humid due to varying contribution from summer and winter monsoons.

High humidity, especially in the summers, may have provided a seasonally selective advantage for individuals better able to functionally activate more eccrine glands and thus sweat more effectively (Kuno, 1956). To explore this hypothesis, greater precision on when and where the allele was under selection—perhaps using ancient DNA sources—in conjunction with more detailed archaeological and climatic data are needed.

A climate adaptation is always a good bet. The problem I have with this hypothesis is that modern day gradients in the distribution of this allele are exactly the reverse of what one might expect in terms of adaptation to heat and humidity. Additionally, is there no cost to this adaptation? After the initial sweep upward, the populations where the derived EDAR mutant is found in high frequencies went through the incredible cold of the Last Glacial Maximum, and groups like the Yakuts are known to have cold adaptations today. Not only that, but the Amerindians from the arctic to the tropics all exhibit a cold adapted body morphology, the historical consequence of the long sojourn in Berengia.

Granted, the authors are not so simplistic, and the somewhat disjointed discussion alludes to the fact that EDAR has numerous phenotypic effects, and it may be subject to diverse positive selection pressures. This seems plausible on the surface, but this complexity of mechanism seems ill-fitted to the fact that the signal of selection around this locus is so clean and crisp. It seems that this is not going to be an easy story to unpack, and there’s a good deal of implicit acknowledgement of that fact in this paper. But tacked right at the end of the main text is this whopper:

It is worth noting that largely invisible structural changes resulting from the 370A allele that might confer functional advantage, such as increased eccrine gland number, are directly linked to visually obvious traits such as hair phenotypes and breast size. This creates conditions in which biases in mate preference could rapidly evolve and reinforce more direct competitive advantages. Consequently, the cumulative selective force acting over time on diverse traits caused by a single pleiotropic mutation could have driven the rise and spread of 370A.

A simple takeaway is that the initial climatic adaptation may have given way to a cultural/sexual selective adaptation, whereby there was a preference for “good hair” as exemplified by pre-Western East Asian canons (black and lustrous), as well as a bias toward small breasts. This aspect gets picked up in The New York Times piece of course. I’ll quote again:

But Joshua Akey, a geneticist at the University of Washington in Seattle, said he thought the more likely cause of the gene’s spread among East Asians was sexual selection. Thick hair and small breasts are visible sexual signals which, if preferred by men, could quickly become more common as the carriers had more children. The genes underlying conspicuous traits, like blue eyes and blond hair in Europeans, have very strong signals of selection, Dr. Akey said, and the sexually visible effects of EDAR are likely to have been stronger drivers of natural selection than sweat glands.

The passage here is ambiguous because the author of the article, Nick Wade, doesn’t use quotes, and I don’t know what is Akey and what is Wade’s gloss on Akey. For example, for theoretical reasons of reproductive skew (a few men can have many children) in general sexual selection is considered to be driven most often by female preference for male phenotypes. I assume Akey knows this, so I suspect that that section is Wade’s gloss (albeit, a reasonable one given the proposition of preference for smaller breasts). The main question on my mind is how seriously prominent population geneticists such as Joshua Akey actually take sexual selection to be as a force driving variation and selection in human populations. It seems that quite often sexual selection is presented as a deus ex machina. A phenomenon which can rescue our confusion as to the origins of a particular suite of traits. But our assessment of the likelihood of sexual selection presumably has to be premised on prior expectations informed by a balance of different forces one can gauge from the literature, and here my knowledge of the current sexual selection literature is weak. Perhaps my skepticism is premised on my ignorance, and the population geneticists who proffer up this explanation are more informed as to the state of the literature.

All this brings me back to the farcical title. When this paper first made news last week I was having dinner with a friend of Japanese heritage (who spent his elementary school years in Japan). I asked him point blank, “Do you like small breasts?” His initial response was “WTF!?! Razib,” but as a mouse geneticist he understood the thrust of my question after I outlined the above results to him. From personal communication with many East Asian American males I am not convinced that there is a overwhelmingly strong preference for small breasts within this subset of the population. But the key here is American. These are individuals immersed in American culture. The norms no doubt differ in East Asia. The typical visual representation of celebrity East Asian females that we see in the American media depict individuals who are slimmer and more understated in their secondary sexual characteristics than is the norm among Western female celebrities (e.g., Gong Li, the new crop of Korean pop stars, even taking into account the plastc surgery of the latter). Part of this is no doubt the reality that the normal range of variation across the population differs, and part of it may be the nature of aesthetic preferences.

But the possibility of deep rooted psychological reasons driving sexual selection (to my knowledge there was no culture which spanned South China and Siberia) brings us back to old ideas about the Pleistocene mind. And, it brings us back to evolutionary psychology, a field which is the whipping boy of both skeptics of the utility of evolutionary science in understanding human nature, and rigorous practitioners of evolutionary biology. And yet here it is not the evolutionary psychologists, but rock-ribbed statistical geneticists who I often see being quoted in the media invoking sexual selection. But do we know it is sexual selection, or is it just our best guess? Because more often than not best guesses are wrong (though best guesses are much more likely to be right than worst guesses!).

Evolutionary genomics has come a long way in the past 10 years. We know, for example, the genetic architecture and some aspects of the natural history of many traits. But, there are still shortcomings. Lactase persistence is the exception to the rule. Even a phenotype as straightforward as human pigmentation has no undisputed answer as to why it has been the repeated target of selection across Eurasia over the past 40,000 years. Oftentimes the right answer is simply that we just don’t know.

Citation: http://dx.doi.org/10.1016/j.cell.2013.01.016

  • TheBrett

    Not only that, but the Amerindians from the arctic to the tropics all exhibit a cold adapted body morphology, the historical consequence of the long sojourn in Berengia.

    Is that still the accepted theory on how the ancestors of the Amerindians made it into the Americas? I thought it was standing on weaker ground more recently.

    (e.g., Gong Li, the new crop of Korean pop stars, even taking into account the plastc surgery of the latter).

    That plastic surgery can be a little weird to see at times, particularly on Girls Generation. I was watching the “Oh!” music video, and all of them except one girl looked extremely similar – similar pointed chin, similar body shape, and so forth. It looked really strange.

    From personal communication with many East Asian American males I am not convinced that there is a overwhelmingly strong preference for small breasts within this subset of the population. But the key here is American. These are individuals immersed in American culture. The norms no doubt differ in East Asia.

    Even then, we’re talking about a population that is significantly larger and greatly removed in both culture and time from the original populations that developed these traits. Would looking at their norms now really be useful? They might have just developed after the fact in a population with genetic propensities towards small breasts.

    And I’m not sure whether the whole “slim, small-breasted” thing is popular outside of Japan and Korea in East Asia. It seems particularly strong in Japan (along with a youth fixation that can be kind of creepy – look at the idol business), and countries whose cultures were heavily shaped by Japanese occupation (Korea).

    • razibkhan

      Is that still the accepted theory on how the ancestors of the Amerindians made it into the Americas? I thought it was standing on weaker ground more recently

      yes. the ‘coastal route’ is just a modification. the soulutrean model is still really heterodox.

    • ChuckRamone

      Culture has traditionally flowed from China to Japan, mostly via the Korean peninsula. The Japanese occupation of the Korean peninsula was only a period of about 35 years (1910-1945). East Asian history stretches back hundreds, thousands of years. And I don’t see as strong a predilection for the ‘Lolita’ thing in South Korea as there is in Japan.

  • ohwilleke

    My first instinct would be that the driver is bubonic plague. EDAR is operative on sweat glands. Plague strikes most prominently in lymph nodes like sweat glands and those found in a woman’s breast. Lymph nodes are also centers of immune response. Bubonic plague, phylogenetically has been tracked to an origin in China, but it probably had lower lethality in its place of origin for thousands of years once the selective sweep happened. If EDAR has any protective effect allowing people to survive plague, it would be strongly selected for.

    The Black Death originated in or near China and spread from Italy and then throughout other European countries. Research published in 2002 suggests that it began in the spring of 1346 in the steppe region, where a plague reservoir stretches from the north-western shore of the Caspian Sea into southern Russia. The Mongols had cut off the trade route, the Silk Road, between China and Europe which halted the spread of the Black Death from eastern Russia to Western Europe. The epidemic began with an attack that Mongols launched on the Italian merchant’s last trading station in the region, Caffa in the Crimea.”

    Eventually, it would resurge to be deadly again in China as well as Europe in the 14th century, but earlier waves of a pre-14th century mutation version could have led to the selective sweeps in EDAR.

    Bubonic plague is extremely lethal and hence a powerful selective force, in the first few rounds of outbreaks, until some form of resistance develops. Bubonic plague doesn’t reach Europe until the current era, about 3000 years+ before East Eurasian admixture with West Eurasians takes place, so it would not have been a site under recent selective pressure in Europe and may have been moribund in much of the place where it was originally a force of intense selective pressure due to herd immunity and genetic adaptations like EDAR.

    Per Wikipedia on N which is the dominant Uralic haplogroup with the Uralic people being those most likely to have brought East Eurasian traits to Europe:

    “Haplogroup N-M231 is a descendant haplogroup of Haplogroup NO. It is considered relatively young, having populated the north of Eurasia after the last Ice Age. Males carrying the marker apparently moved northwards as the climate warmed in the Holocene. The absence of haplogroup N-M231 in the Americas indicates that its spread across Asia happened after the submergence of the Bering land bridge (Chiaroni 2009). It is suggested that it arose in southeast Asia 19.4±4.8 ky years ago, and then migrated in a counter-clockwise path from modern day regions of Mongolia and northern China to as far as northeastern Europe (Rootsi 2006).”

    Perhaps Y-DNA hg N actually arose to the north of China (at a time when the plague was absent to the north of China) and then filtered into the Han to the South over time, and then expanded into Southeast Asia with Han Chinese expansion rather than the suggested counterclockwise pattern from Southeast Asia. This fits with the notion that North Asians are some of the least sweaty/oily peoples in the world presumably due to some much milder selective pressure – which wouldn’t be the case if they had EDAR.

    N has a strongly Northern distribution now and an expansions that pre-Mongol invasions (after Uralic admixture in Europe) may have been less mixed into the more Southern Han Chinese population genetics ca. 5000 years BP than it is now. Turkic expansion then brings plague from China to someplace in Europe where it can thrive.

    • razibkhan

      My first instinct would be that the driver is bubonic plague

      EDAR was found in the 3,500 year old greenlander remains. i’m skeptical of plague being common in pre-agricultural populations for reasons of density.

      • ohwilleke

        As you note, the notion that sexual selection for small breasts and sleek black hair purely on the basis of a fashion fad had an effect rivaling genes for things like malaria resistance and lactose persistance isn’t a very good candidate either. To get that intense a selection factor you need a deadly menance that the gene addresses in some way.

        Clearly, the derived version of EDAR reached fixation in East Asian populations pre-LGM. The density may not have been at Neolithic levels, but the domestication of the dog around that time probably simultaneously increased hunter-gatherer band size and provided a vector for flea transmission (and even a decimated tribe would also probably bring its dogs with it as its remaining members tried to join up with some sister tribe).

        It also isn’t impossible that, like the contemporaneous and nearby Jomon of Japan, that the plauge could have arisen in semi-sedentary fishing communities which would have been the most dense populations until the Neolithic revolution (particularly if those villages had dogs that would have improved their security and food gathering and provided an edge over prior Paleolithic cultures in the region). Fishing communities like the Jomon and Pitted Ware (and antecedent Comb Ceramic culture) in NE Europe were stable and specialized enough that they developed pottery in the absence of food production via farming and herding.

        The Greenland example is right on point. That 3,500 year old Greenlander wasn’t part of a wandering band of mammoth hunters. The society that he came from was closer to that of the Native Americans of the Pacific Northwest or the Eskimos that replaced his people in that ecological niche – semi-sedentary fishmen/seal hunters/sea bird hunters who lived in fairly stable village sized encampments. Notably, Inuit population density was sufficiently great for the infectious diseases that they received from Basque whalers at first contract with Europeans to spread and devistate them rather than peetering out.

        • razibkhan

          disease is always a good candidate IMO. but i’m not sure about the details in this case that you’re outlining.

        • ohwilleke

          Low levels of body hair in Asians (apart from N. Asian derived Ainu) could arise from the same selective sweep as a way to reduce attractiveness to fleas.

  • http://www.gwern.net/ gwern

    > The norms no doubt differ in East Asia.

    Reminds me of this recent article on anti-breast prejudice in North Korea and an old Japanese insult ‘bird-chested’: http://www.examiner.com/article/north-korean-women-forced-to-hide-their-large-breasts

  • http://skadhitheravernerblog.wordpress.com/ Skadhi_the_Raverner

    The epicanthic fold is simply the result of lack of height development of the nasal root, there is no mystery there. Not everything is an adaptation in itself.

    • razibkhan

      who said it was an adaptation? don’t read something into a statement that wasn’t there (GWAS != adaptation).

    • Paul Conroy

      Skadhi,
      I’m not sure if that’s correct… I have a high-bridged nose and a partial epicantic fold, which is relatively common in Northern Europe…

    • nah
  • Paul Conroy

    To me it seems most likely that denser milk production ducts –> yields smaller breasts, with smaller surface area –> another cold adaption

    • http://www.facebook.com/karl.zimmerman Karl Zimmerman

      I would guess there might be a relationship between Asian small breast size and the comparative lack of sweat, given milk glands are ultimately highly modified sweat glands themselves.

  • Paul Conroy

    Also, one only need look at the Gangnam Style video, and see the svelte form of the Korean dancing girls, and the alternate video in Korean, featuring the lead dancer “Hyuna” – who is a major star in her own right, and seems to sport barely an A-cup…

    http://www.youtube.com/watch?v=wcLNteez3c4

    Of course PSY has the classic Cold Adapted physique – short limbs and neck, large spherical head,and thick body.

    • razibkhan

      yes. but cultural norms change fast. see: eyelid surgery + hair tinting.

    • Sandgroper

      It’s a fine bit of self-satire by Kim Hyun-a. Having been drowned in the Korean wave, I almost prefer her version to PSY’s original.

  • Davidski

    I haven’t thought this through too much, but maybe this derived East Asian form of EDAR isn’t present in Europeans because Europeans don’t have East Asian admixture?

    In other words, the component shared by Europeans with South Amerindians, and to a lesser extent with Siberians and East Asians, possibly came from a now extinct third party in Siberia. It might have been picked up by the (East Asian EDAR carrying) ancestors of Amerindians as they moved into the Americas. In fact, perhaps this mysterious Siberian group effectively blocked the entry of any (East Asian EDAR carrying) East Eurasians proper into Europe?

    So the other thing I’m getting at is that Amerindians and East Eurasians might be ancient hybrid groups, just like Europeans and South Asians. I think I even read somewhere, maybe at Dienekes, that Reich was preparing a paper about that.

    • razibkhan

      none of those propositions strike me as crazy. alas, little does these days….

  • Karch_Buttreau

    To clarify, “thick” hair wrt EDAR means that an individual strand of hair is thicker, and hair as a whole becomes more sparse. I have a tough time getting it through my head that thick/sparse hair attribute of EDAR is good looking / sexually selected, but as you mention, there are other attributes.

    I also recall reading that the EDAR gene was thought to be present in Homo Erectus (I guess by looking at the incisors). In fact, I can see that you posted on it a couple of years ago.

    BTW, I carry one EDAR gene mutation. Saves money on combs, LOL.

    • razibkhan

      we don’t know the genetic architecture of shovel-shaped incisors in neandertals. probably was different…but intriguing, as it may be similar adaptations with similar side effects?

  • BoggleMinds

    I’d be interested to see if there’s any correlation or relationship between the paper’s findings and the generalized observation that East Asians are highly neotenous (compared to other groups). It’s not clear whether there’s any connection between neoteny and the EDAR locus, and then there’s the added complexity of possible sexual selection working as a confounding factor.

    I agree that it’s a really difficult task to come up with hypotheses to *explain* these results convincingly. It’s like we’ve now successfully discovered *what* has probably happened to a first approximation, and the real challenge then becomes explaining how and *why* it happened to a deeper level. Evolutionary psychologists need not apply though.

  • UncleTomRukusInWhiteHeaven

    My experience living in East Asia, where I will return in less than a month is that most Asian men don’t pay much attention to women’s breast size or bodies, other than “fat or skinny”, they prefer skinny and tend to prefer longer hair. Men in the region (and I’ve lived in Singapore, Taiwan, China, and Japan) will call a woman beautiful almost solely based on her face. Western men definitely focus more on a woman’s body. The only Asians I know who seem to love large breasts are Japanese, but that is mostly in porn, but if you look at pop-stars most do not have large breasts at all, and neither does the average woman.

    As far as sweat glans, I found this weird, because it is a common stereotype in Japan that foreigners (in the Japanese context this is usually white people and maybe black) sweat a lot and when they sweat they smell like “meat or milk”, and that Japanese do not sweat. My ex-wife was Japanese, and I can tell you for a fact she rarely sweat, and Japanese think intensive sweating, the way you see a lot of white people sweat in the summer when doing outdoor activity is considered an potential “illness” in Japan. I also noticed that East Asians don’t sweat much, whereas many white Euro types look like you someone threw a bucket of water on them, black Americans (not sure about Africans) tend to be in-between in my experience.

    We lived in Tokyo, but my ex was from Nagano, which has a mountainous temperate climate, not like the sea-level humidity of coastal Eastern Japan.

  • UncleTomRukusInWhiteHeaven

    I don’t wish to get into crass detail, but Gong Li does not exactly qualify as having small breasts…although I do agree with you most popular East Asian actresses do. Gong Li was never very popular in China anyway. She is probably more famous for being a “xiaosan” (mistress) than an actress, but that’s another story.

    http://www.outie.net/forums/attach/xinsrc_3410012715200932349148.jpg

  • anonymous.commenter

    Or maybe the first settlers of the Americas — and the Amerindian-like population that admixed with ancient Europeans — lacked/had very low frequencies of the derived EDAR variant, and it only subsequently swept to high frequency, following its introduction in a later wave of movement from East Eurasia and/or some pronounced (continent-wide?) shift in selective regime … whatever that would be.

    EDAR’s sole skeletally-evident effects, so far as I can tell, are in dentition. And what do we see there?

    According to Turner and colleagues, modern Amerindians have very high (he says the world’s highest) frequencies of winging (50% — hasn’t been explicitly EDAR-associated at present), shoveling (85-90%), and double shoveling (55-70%) in the maxillary central incisors. These same features are frequently either absent or much less pronounced in degree in Paleoamerican remains, which also have elevated incidence of things like Cusp of Carabelli that are notably rare in contemporary Amerindian pops. Some workers would go so far as to see these Paleoamerican remains as largely “Sundadont” but that whole Sino-/Sunda- dichotomy is shaky … unambiguous assignment is often impossible.

    So the picture’s ambiguous. Let’s get direct EDAR info for some guys older than Saqqaq.

  • Luis Aldamiz

    I for one agree that the selection sweep proposal seems very inconsistent with the trait’s distribution and would think instead of an ancient founder effect at the origins of East Asians as macro-population (or, if you wish, the “Mongoloid race”).

    I also agree that the apparent lack in Europeans including, it seems from the map, Northern Russians, whose low level Siberian affinities are well know, is very strange. Very tentatively, instead of lack of admixture, what seems unsustainable for those populations on light of other data, I’d suggest to explore a different kind of sociological selective mechanism that I’d call “racist selection”. I.e. internalized racist prejudices in an admixed population could cause the individuals with phenotypes approaching the disliked one to suffer greater levels of marginalization (everything else equal) along millennia, even within their families, gradually pushing out those traits (but not really affecting that much the overall level of admixture in the genome). Sexual selection would be part of it but not exclusively. It’d be a selection against this trait, not for it obviously. Food for thought at least.

    It’d be interesting to know the EDAR frequencies among Finnic peoples who retain language and identity for example. If my idea is correct, it may have begun within them or be also something more recent only affecting Russian-speaking populations (or both).

  • ChuckRamone

    Is dry-type ear wax connected to EDAR? That too is a trait I’ve read is mostly found in East Asians and Native Americans.

    • anonn

      No connection demonstrated. ABCC11 is the more obvious determinant of dry earwax (and low axillary odor).

  • http://socioproctology.blogpost.com windwheel

    I don’t understand why male preferences would put selection pressure on female morphology. Surely, by Bateman’s principle, only female preferences would be relevant? Perhaps, smaller breasts meant quicker weaning which meant more kids, so that the small breasted out bred the large breasted?

    Alternatively, on the hypothesis that ugly women only get lucky with drunk men, perhaps alcohol intolerance is to blame!

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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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