Category: Human Population Genetics

Turks are Anatolian under the hood, somewhat more Greek than Armenian

Posted on by Razib Khan

My post, Are Turks Armenians Under The Hood?, attracted a little bit of controversy. The main criticism, which was a valid one, is that I did not sample Anatolian Greeks. A reader passed on three Anatolian Greek samples. I also added a Cypriot data set. To my mild surprise, the Anatolian Greeks and Cypriots cluster together, at the end of the Greece cline toward West Asians. Therefore, for further analysis, I pooled the three Greeks with the Cypriots.

Additionally, there are two Balkan Turk samples. Even on the PCA it’s pretty clear that they’re genetically very different from the other Turks (one of them is from what has become Bulgaria), though the shift toward East Asians indicates that Turkification is very rarely a matter purely of religious conversion to Islam and assimilation of the Turkish language (obviously it initially is for many people, but these people then intermarry with those with some East Asian ancestry).

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Demographic replacement in Southeast Asia during the Holocene

Posted on by Razib Khan

Well sometimes you feel silly, and it’s not your fault. Yesterday our podcast on Sundaland went live (we talked about Doggerland and Beringia too!). Though I expressed a fair amount of skepticism, I took the argument that Stephen Oppenheimer presented in Eden of the East, that modern Austronesians are long-term residents of Southeast Asia, seriously.

The alternative view, most forcefully put by Peter Bellwood in books such as First Farmers, is that Austro-Asiatic and Austronesian people were agriculturalists issuing out of southern China that transformed the region over the past 4,000 years (the Austronesians from Taiwan specifically, though during the Pleistocene Taiwan was connected to the mainland).

I lean toward Bellwood’s view, and today a preprint came out which basically confirms it in totality, Ancient Genomics Reveals Four Prehistoric Migration Waves into Southeast Asia. The abstract:

Two distinct population models have been put forward to explain present-day human diversity in Southeast Asia. The first model proposes long-term continuity (Regional Continuity model) while the other suggests two waves of dispersal (Two Layer model). Here, we use whole-genome capture in combination with shotgun sequencing to generate 25 ancient human genome sequences from mainland and island Southeast Asia, and directly test the two competing hypotheses. We find that early genomes from Hoabinhian hunter-gatherer contexts in Laos and Malaysia have genetic affinities with the Onge hunter-gatherers from the Andaman Islands, while Southeast Asian Neolithic farmers have a distinct East Asian genomic ancestry related to present-day Austroasiatic-speaking populations. We also identify two further migratory events, consistent with the expansion of speakers of Austronesian languages into Island Southeast Asia ca. 4 kya, and the expansion by East Asians into northern Vietnam ca. 2 kya. These findings support the Two Layer model for the early peopling of Southeast Asia and highlight the complexities of dispersal patterns from East Asia.

The transition to full-fledged rice agriculture occurred in Vietnam ~4,000 years ago. In First Farmers Bellwood reports on an archaeological site dating to that period where skeletal evidence has been adduced to record the presence of both Northeast Asian and Australo-Melanesian types. These results make clear though that these hunter-gatherers in Southeast Asia are more similar to the Onge of the Andaman Islands, as well as the Negritos of the interior of the Malay peninsula. They’re totally in alignment with the earlier morphological results (also, readers might be curious to know that one site of the Hoabinhian culture is in Yunnan, China). This shouldn’t be surprising, as the Andaman Islands were a peninsula which extended from southern Burma during the Pleistocene.

Already the most accepted model for the introduction of intensive agriculture into Southeast Asia is that it was brought by Austro-Asiatic peoples. These results confirm that. Additionally, it seems clear that Austro-Asiatic ancestry made it to island Southeast Asia, whether directly or through Austronesian admixture before arriving in island Southeast Asia. Java and Bali have some of the higher fractions ancestries most closely associated with Austro-Asiatic groups on the mainland.

Deeper digging into the admixture distributions has long made it pretty evident that some areas had much higher Austronesian fractions in Indonesia than others, and it wasn’t just a function of distance from the Phillippines. Why? My own hunch is that Austronesians brought social and cultural systems which were better adapted to island Southeast Asia, and were more fully able to exploit the local ecology. Meanwhile, aside from a few fringe areas such as the Malay peninsula and coastal Vietnam, they were not successful on the mainland.

The authors also detect migrations into Southeast Asia besides that of the Austro-Asiatics and Austronesians. One element seems correlated with the Tai migrations, and another with Sino-Tibetan peoples, most clearly represented in Southeast Asia by the Burmans. The excellent book, Strange Parallels: Volume 1, Integration on the Mainland: Southeast Asia in Global Context, c.800–1830, recounts the importance of the great migrations of the Tai people into Southeast Asia ~1000 A.D. Modern-day Thailand was once a flourishing center of Mon civilization, an Austro-Asiatic people related to the Khmers of Cambodia. The migrations out of the Tai highlands of southern China reshaped the ethnography of the central regions of mainland Southeast Asia. The Tai also attempted to take over the kingdoms of the Burmans. Though they failed in this, the Shan states of the highlands are the remnants of these attempts (tendrils of the Tai migrations made it to India, the Ahom people of Assam were Tai). Vietnam, shielded by the Annamese Cordillera, came through this period relatively intact. It is also well known that Cambodia’s persistence down to the present has much to do with the shielding it received from France in the 19th century in the wake of Thai expansion.

There are two bigger issues that this paper sheds light on. One is spatial, and the other is temporal.

They detect shared drift between Austro-Asiatic people and tribal populations in northeast India. This is not surprising. A 2011 paper found that Munda speaking peoples, whose variant of Austro-Asiatic is very different from that of Southeast Asia, are predominant carriers of Y chromosome O2a. This is very rare in Indo-European speaking populations, and nearly absent in Dravidian speaking groups. Additionally, their genome-wide patterns indicate some East Asian admixture, albeit a minority, while they carry the derived variant of EDAR, which peaks in Northeast Asia.

One debate in relation to the Munda people is whether they are primal and indigenous, or whether they are intrusive. The genetic data strongly point to the likelihood that they are intrusive. An earlier estimate of coalescence for O2a in South Asia suggested a deep history, but these dates have always been sensitive to assumptions, and more recent analysis of O2a diversity suggests that the locus is mainland Southeast Asia.

Now that archaeology and ancient DNA confirm Austro-Asiatic intrusion into northern Vietnam ~4,000 years ago, I think it also sheds light on when these peoples arrived in India. That is, they arrived < 4,000 years ago. As widespread intensive agriculture came to Burma ~3,500 years ago, I think that makes it likely that Munda peoples arrived in South Asia around this period.

I now believe it is likely that the presence of Austro-Asiatic, Dravidian, and Indo-Aryan languages in India proper was a feature of the period after ~4,000 years ago. None of the languages of the hunter-gatherer populations of the subcontinent remain, with the possible exception of isolates such as Nihali and Kusunda.

The temporal issue has to do with the affinities of these peoples, and how they relate to the settling of Eastern Eurasia. All the Southeast Asian groups after the original Australo-Melanesians share more of an affinity with the Tianyuan individual than Papuans. The implication here is that Tianyuan is closer to the ancestors of various agriculturalists in Southeast Asia than just some random basal Eastern Eurasian. But, since Tianyuan dates to 40,000 years ago, and, is from the Beijing region, it is hard to make strong inferences from comparisons with only it. The heartland of ancient Chinese culture in Henan was to the south of the Tianyuan, after all. More samples are needed before one can truly tease out the pattern of isolation-by-distance vs. admixture that led to the emergence of the proto-farmer populations which settled Southeast Asia.

In the podcast above one thing that came up is that a lot of genetic data indicate decreased diversity as one moves from the south to the north in East Asia. This has long been taken to mean that humans migrated north, and so were subject to bottleneck effects. I pointed out that this may simply be a consequence of admixture between two very different groups of people in Southeast Asia, elevating diversity statistics.

And yet as the map at the end of the preprint suggests it is highly plausible that Pleistocene Asia was marked by a south to north dynamic of migration. The Austro-Asiatic peoples who migrated south during the Holocene may simply have been backtracking the migration of their ancestors. What these results, and ancient DNA more generally, tell us is that humans were often on the move. The Pleistocene world of climate change probably meant that humans had to be on the move.

White modern Northern Europeans are genetically more like brown South Asians than brown(ish) ancient Northern Europeans were

Posted on by Razib Khan

The Guardian has a piece by Arathi Prasad, Thanks to Cheddar Man, I feel more comfortable as a brown Briton. Dr. Prasad is a geneticist, so the science is pretty decent (she’s probably seen the documentary ahead of time too).

But there is a curious quirk here and it reveals something about human psychology: modern Britons are genetically much closer to South Asians, like Arathi Prasad, than these ancient darker-skinned Britons. The plot to the left illustrates this (it’s using the Dystruct package). The far right of the top panels represent South Asians. You can see Europeans pretty clearly. Let’s note two things:

1) Modern Europeans (except for Sardinians) share an orange “steppe” component with most South Asians (these are no doubt Indo-European migrations of the Bronze Age)

2) The brown element represents European hunter-gatherers. This element is found at varying quantities across Europe, with the lowest fractions in Sardinians. Though present in South Asians (this may or may not be an artifact to be honest), it’s not present at very high frequencies.

One always has to be careful about taking these proportions as literal representations of ancestral populations. They are not. But what they show is that modern Northern Europeans and South Asians have been touched by the same population movements over the past 5,000 years, and so are genetically much closer than the people who lived in Northern Europe and South Asia 5,000 years ago.

Humans are a visual species. In a pre-modern environment, physical cues were important for group identity, though I suspect just as much due to scarification and tattooing as phenotypic differences due to biology. The fact that Cheddar Man, and Paleolithic hunter-gatherers in Western Europe more generally, probably resembled modern South Asians more than they do modern Northern Europeans (I think they were more likely to be olive-brown than dark-brown, but I’m not confident), is more salient to human folk biology than the fact that modern Northern Europeans are much closer genetically to South Asians than the more “brown” ancient Northern Europeans.

Stuff like this always reminds me of the deep wisdom in Artur C. Clarke’s Childhood’s End. The ultimately benevolent alien species which mentored humanity shielded us from their physical appearance because the knew we’d find it horrifying. The substance of what they did for us, who they were, was going to be less important to immature humans than the fact of what they looked like.

Note: Fst between Sindhi from Pakistan and WHG (Cheddar Man was one) is 0.087. Sindhi from Pakistan and English is 0.023. English to WHG is 0.058 (source). Fst can not be naively interpreted as “genetic distance.” But, this gets at the fact that Mesolithic European hunter-gatherers were very distant from modern South Asians. And widespread gene flow and admixture over the past 5,000 has compressed a lot of genetic differences which were starker across geography in the past.

Ancient DNA and Dystruct

Posted on by Razib Khan


There’s a new preprint, Inference of population structure from ancient DNA, which uses explicit demographic models to make inferences about ancestry. I haven’t dug into the guts of the math, but, the outputs are quite interesting.

What seems to be obvious is that Western Eurasia has a much richer set of models to choose from than elsewhere. European, Middle Eastern and South Asian populations exhibit the greatest difference between Dystruct and Admixture.

Five things paleogenetics tells us about the human past

Posted on by Razib Khan

Since I’m flogging Enlightenment Now, I thought perhaps I should remind readers that Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past by David Reich is out in 1.5 months. For years people have asked me about a book to read to understand what genetics has to say about human history. This is that book.

And yet before you get there, what do you need to know?

Here are five things you should know. Five things that we know with a very high degree of certitude.

  1. Many (most?) modern populations clusters we perceive as clear and distinct date to the last 5,000 years. To give a concrete example, the genetics that we find to be typical of Northern Europeans only comes into being ~5,000 years ago, with the Corded Ware populations. To my knowledge none of the prior populations along the North European plain exhibit the mix of characteristics and ancestries typical of modern Northern Europeans in any way, shape, or form.
  2. Concomitantly, many of the physical characteristics we find typical of modern populations are probably relatively recent configurations due to natural selection.
  3. Non-African populations, whether European, Middle Eastern, South Asian, (South)East Asian, Amerindian or Oceanian, derive from a population expansion that dates to ~50,000 years BP. These populations experienced a bottleneck on the order of 1,000 to 10,000 breeding individuals.
  4. Modern humans are old. Population structure within Africa of modern humans dates to at least 200,000 years before the present, and perhaps even earlier.
  5. Population turnover was ubiquitous. Change was the only constant.

When Western Near Eastern Farmers carried North Eurasian Y chromosomes into Central Africa

Posted on by Razib Khan


Whenever you look at a map which shows the distribution of Y chromosomal haplogroup R1b you see two areas where the frequency seems very high. First, Western Europe has a very high frequency. Before 2010 it was commonly assumed that R1b was the heritage of late Pleistocene European hunter-gatherers. Around 2010 deeper analysis suggested perhaps that this was not so, and that the deepest divisions in the phylogeny of Eurasian R1b could be found to the east. The high frequency of this haplogroup then may have been an artifact of the Holocene.

Ancient DNA has confirmed this hypothesis. The high frequency of R1b in Western Europe seems to date to the Bronze Age. Though R1b is not found exclusively in Indo-European peoples and existed at low frequencies in Pleistocene Europe, its current ubiquity in Europe seems likely related to demographic turnover between 3 and 5 thousand years ago.

If I had to bet I think R1b, like R1a, originates among the North Eurasian people who mixed with West Eurasians and Amerindians. The Ma’lta boy, for example, seems to have been a basal R.

But notice a secondary mode of R1b in Africa. This is R-V88. The highest frequencies of this Y chromosomal haplogroup are found in Chadic speaking populations. Chadic is a basal group in the Afro-Asiatic language family. A few years ago a paper was published using autosomal DNA on Chad populations and suggested that Eurasian backflow occurred in deep antiquity. From that paper:

We estimate that [autosomal] mixture occurred 4,750–7,200 ya, thus after the Neolithic transition in the Near East…In Chad, we found a Y chromosome lineage (R1b-V88) that we estimate emerged during the same period 5,700–7,300 ya

A new paper, The peopling of the last Green Sahara revealed by high-coverage resequencing of trans-Saharan patrilineages, really gets to the origin of R-V88, with a massive Y data-set. There’s a lot of other Y lineages that are surveyed in this work, but in the supplements, the figure makes it clear that Sardinian R-V88 is basal to star-like African topologies. The implication here is that the African lineages derive from European ones.

The autosomal paper found Chad populations (though the one in question was not Chadic speaking) seem to share drift from Sardinians in particular. Looking at ancient genomes Early European Farmers seem to have been the primary donor population. Additionally, the coalescence of the African lineages seems to date to 5 to 6 thousand years before the present.

Though not definitive, the association of Afro-Asiatic populations with R-V88 is strongly suggestive to me of the possibility that some western Near Eastern Farmers spoke Afro-Asiatic languages.

No one understands the targets of selection in humans (except disease)

Posted on by Razib Khan

I’m proposing on an upcoming episode of The Insight that we should talk about natural selection in the context of humans. The reason is that there seems to be a lot of it. It may even be ubiquitous. But, in most cases which aren’t trivial, we have no good idea what’s going on.

By not being trivial, I mean when there is selection on loci implicated in immunological variation in response, it’s pretty clear what’s going on. Infection by pathogens is arguably the reason that humans have sex, where some sort of frequency-dependent selection is obvious.

When it comes to something like lactose tolerance (lactase persistence), the genomic evidence seems indisputable that there was natural selection (a very long haplotype in Eurasia sweeping up in frequency recently). And there’s a reasonably plausible story. The adoption of agro-pastoralism by disparate populations across the world has produced similar adaptions, albeit via different genetic pathways. But, it isn’t as if we have experimental or ecological evidence as to the differential fitness of humans “in the wild” on this trait. Does milk sugar really make that huge of an impact? (disease kills, its selective power is clear)

Then, you have cases like pigmentation where there are numerous explanations which part of the story, but not most of it. And finally, you have situations like the EDAR variant among East Asians and Amerindians where selection seems likely, but there is zero plausible explanation of what the target of selection is.

The genome of “Cheddar Man” is about to be published

Posted on by Razib Khan

If you are American you have probably heard about “Cheddar Man” in Bryan Sykes’ Seven Daughters of Eve. If you don’t know, Cheddar Man is a Mesolithic individual from prehistoric Britain, dating to 9,150 years before the present. Sykes’ DNA analysis concluded that he was mtDNA haplogroup U5, which is found in ~10% of modern Europeans, and which ancient DNA has found to be overwhelmingly dominant among European hunter-gatherers. But for years there has been controversy as to whether this result was contamination (after all, if it’s found in ~10% of modern Europeans it wouldn’t be surprising if the DNA was contaminated).

Today that is a moot point. On February 18th Channel 4 in the UK will premier a documentary that seems to indicate genomic analysis of Cheddar Man’s remains have been performed, and he turns out to be exactly what we would have expected. That is, he’s a “Western Hunter-Gatherer” (WHG) with affinities to the remains from Belgium, Spain, and Central Europe. These WHG populations were themselves relatively recent arrivals in Pleistocene Europe, with connections to some populations in the Near East, and with unexplored minor genetic admixture from an East Asian population. Their total contribution to the ancestry of modern Europeans varies, with lower fractions in the south of the continent, and the highest in the northeast.

Overall, the consensus seems to be that in Western Europe the genuine descent from indigenous hunter-gatherers passed down through admixture with Neolithic farmers, and then the Corded Ware and Bell Beaker groups, is around ~10%. This is the number that shows up in the press write-ups. But, there are some researchers who contend it is far less than 10%, and that that fraction is misattribution due to early admixture with relatives of these hunter-gatherers as steppe and farmer peoples were expanding.

Phylogenetics aside, one of the major headline aspects of the Cheddar Man is that reconstructions are now of a very dark-skinned and blue-eyed individual. Some of the more sensationalist press is declaring that the “first Britons were black!” As far as the depiction goes, this is literally true. The reconstruction is of a black-skinned individual in the sense we’d describe black-skinned.

But on one level it is entirely expected that this is what Cheddar Man would look like. The hunter-gatherers of Mesolithic Western Europe were genetically homogenous. They seem to derive from a small founder population. And, on the pigmentation loci which make modern Europeans very distinctive vis-a-vis other populations, SLC24A5, SLC45A2 and HERC2-OCA2, they were quite different from anything we’ve encountered before. First, these peoples seem to have had a frequency for the genetic variants strongly implicated in blue eyes in modern Europeans close to what you find in the Baltic region. The overwhelming majority carried the derived variant, perhaps even in regions such as Spain, which today are mostly brown-eyed because of the frequency of the ancestral variant. Second, these European hunter-gatherers tended to lack the genetic variants at SLC24A5 and SLC45A2 correlated with lighter skin, which today in European is found at frequencies of ~100% and 95% to 80% respectively.

The reason that one of the scientists being interviewed stated that there was a “76 percent probability that Cheddar Man had blue eyes” is that they used something like IrisPlex. They put in the genetic variants and popped out a probability. The problem is that the training set here is modern groups, which may have a very different genetic architecture than ancient populations. Recent work on Africans and East Asians indicate that the focus on European populations when it comes to pigmentation genetics has left huge lacunae in our understanding of common variants which affect variation in outcome.

East Asians, for example, lack both the derived variants of SLC24A5 and SLC45A2 common in Europeans but are often quite light-skinned. A deeper analysis of the pigmentation architecture of WHG might lead us to conclude that they were an olive or light brown-skinned people. This is my suspicion because modern Arctic peoples are neither pale white nor dark brown, but of various shades of olive.

As far as blue eyes go, it is reasonable that these individuals had that eye color because that trait seems somewhat less polygenic than skin color. There are darker complected people with light eyes, from the famous “Afghan girl” to the first black American Miss America, Vanessa Williams. The homozygote of the derived HERC-OCA2 variant seems relatively penetrant. From what I recall the literature indicates many people with blue eyes are not homozygotes on this locus for the derived haplotypes, but those who are homozygotes for the derived haplotypes invariably have blue eyes.

Addendum: It isn’t clear in the press pieces, but it looks like they got a high coverage genome sequence out of Cheddar Man. They refer to sequencing, and, they seem to have hit all the major pigmentation loci. This indicates reasonable coverage of the genome.

Neanderthal introgression in the ancient DNA age

Posted on by Razib Khan

Over the past ten years or so the idea of “adaptive introgression” in the human context has gone from seeming ludicrous to banal. When I first began entertaining this idea in 2006 some commenters literally heckled me, because the idea of admixture with Neanderthals seemed so ludicrous. Then, in 2010 the maturation of the field of ancient human DNA confirmed that it was likely non-Africans had Neanderthal admixture. Over the next few years, specific instances of introgression were discovered (e.g., EPAS1 from a Denisova-relative).

Today the whole landscape of adaptive introgression from other lineages is now being mapped. An open access paper in Molecular Biology and Evolution, Disentangling Immediate Adaptive Introgression from Selection on Standing Introgressed Variation in Humans, examines the distinction between the immediate sweep of an introgressed allele after admixture, and later selection on alleles which are segregating neutrally within the absorbing population.

The authors developed a statistic which detected “immediate adaptive introgression (iAI).” Instances where alleles increased in frequency immediately after the admixture in the modern human background from Neanderthals (or possibly other archaics?).

One interesting gene was LYPD6B. This seems to have been subject to selection immediately, and it’s widely distributed in modern non-Africans. This locus controls “cholinergic signaling in the brain” and the authors suggest that the “results suggest that selection on this introgressed haplotype may have been due to beneficial behavioral and/or physiological traits.” The other possible cases of iAI seem mostly involved immune response, not entirely surprising.

But perhaps the bigger issue is that there may be a lot of selection on segregating variants that came in from Neanderthals. That is, introgression may be more important for selection on standing variation. This is is probably the dominant mode of adaptation in humans in any case. Think of it is portfolio diversification.

Speaking of variation, there’s a paper in the works which suggests that admixture with Neanderthals replenished some of the genetic diversity that the Out-of-Africa modern lineage lost:

“They left many beneficial variants behind in Africa,” says evolutionary genomicist Tony Capra of Vanderbilt University in Nashville, who reported the results. “Interbreeding with Neandertals provided an opportunity to get back some of those variants, albeit with many potentially weakly deleterious Neandertal alleles as well.”

Why the Chinese don’t buy deodorant

Posted on by Razib Khan

 
In human populations a SNP in ABCC11 is correlated with two salient traits: 1) wet or dry earwax 2) body odor. When I had my first son sequenced before his birth the main variant of phenotypic consequence that I noticed (aside from him being a heterozygote on KITLG), was that he carried a derived mutation on this position. Meaning that he was going to have dry earwax and fewer issues with body odor.

My wife and I are both heterozygotes. This is not too surprising. The derived variant is actually greater than 50% in Bengalis in the 1000 Genomes (in South India the derived variant is also around ~50%), while about ~25% of Northern Europeans are heterozygotes.

This genetic story came to my mind again because of this article in The New York Times, Aiming at China’s Armpits: When Foreign Brands Misfire:

There’s another reason few Chinese consumers buy deodorant: basic biology.

Scientists in recent years have shown that many East Asians, a group that includes China’s ethnic Han majority, have a gene that lowers the likelihood of a strong “human axillary odor” — scientist-speak for body stink.

That lowers the likelihood that they will use deodorant to begin with, according to a 2013 study by researchers at the University of Bristol and Brunel University in Britain, after a survey of nearly 6,500 women of various backgrounds.

“It is likely that deodorant usage is not widely adopted because there is, for much of the East Asia population, no need for it,” it said. (For those curious about such matters, that same genetic difference also leads to drier earwax.)

A friend of mine in undergrad of East Asian background told me once that she had never worn deodorant. So this shouldn’t be very surprising.

Today I found a paper, A missense variant of the ABCC11 gene is associated with Axillary Osmidrosis susceptibility and clinical phenotypes in the Chinese Han Population, which explicitly probes the correlation between body odor (“Axillary Osmidrosis”) and the SNP in question in the Han Chinese population.

The chart below makes the association obvious:

The correlation between carrying the G, ancestral, allele, and body odor is very strong. Though it is imperfect. Going through this literature human smells are clearly a polygenic trait (see The effect of ethnicity on human axillary odorant production). That being said, this case-control study in a Han population shows ABCC11‘s importance in at least East Asian populations (earlier work in Japan showed that those with body odor tended to have wet earwax and carry the G allele as well).

In regards to the genotype proportions the authors observe:

The excessive heterozygosity observed in AO individuals is probably due to the effect of selection, particularly nonrandom mating against AO phenotype.

This doesn’t make sense to me. Wouldn’t people who have body odor tend to pair up in a society where they are a minority? The authors note that the excess of heterozygotes was observed in earlier studies too.

If you dig into the frequencies it seems that the derived mutation is absent among populations in Africa without recent Eurasian back-migration. I looked it up, and it’s segregating in ancient Eurasian samples, with Ust Ishim being a heterozygote. It is curious that in no population has the derived frequency swept to fixation, nor has the ancestral variant fixed in other groups (such as in Europe).

I strongly doubt that there is any selection on this locus due to earwax or body odor. It is a pleiotropic locus, there are other effects from the mutation. One of those other effects is probably the target of any selection. And in regards to selection, it seems likely that that would be a balancing sort since neither the ancestral nor the derived variant are fixed in most populations.