The Unz Review: An Alternative Media Selection
A Collection of Interesting, Important, and Controversial Perspectives Largely Excluded from the American Mainstream Media
 TeasersGene Expression Blog
Descent and Selection Is a Bugger: Black Kurgans?
🔊 Listen RSS
Email This Page to Someone

 Remember My Information



=>

Bookmark Toggle AllToCAdd to LibraryRemove from Library • BShow CommentNext New CommentNext New ReplyRead More
ReplyAgree/Disagree/Etc. More... This Commenter This Thread Hide Thread Display All Comments
AgreeDisagreeLOLTroll
These buttons register your public Agreement, Disagreement, Troll, or LOL with the selected comment. They are ONLY available to recent, frequent commenters who have saved their Name+Email using the 'Remember My Information' checkbox, and may also ONLY be used once per hour.
Ignore Commenter Follow Commenter
Search Text Case Sensitive  Exact Words  Include Comments
List of Bookmarks
Ukraine

Citation: Wilde et al.

Credit: Igor Kruglenko

Credit: Igor Kruglenko

A new paper in PNAS, Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 years, uses ancient DNA to examine the possibility of very recent natural selection in Europeans. In particular, it focuses on eastern Europeans, and roughly a region coterminous with Ukraine ~6000 to ~4000 years ago. The sample seems somewhat biased toward the low end of the age range if you look the supplemental tables. In the paper itself (which is open access) I don’t see a map to get a sense of the distribution of the sites from which the DNA was extracted. So I took the supplemental table and used the latitude and longitude information, as well as the samples from each site, and produced a density map with a bubble plot overlain upon it with specific locations (size of bubble proportional to number of samples at site). Like the earlier ancient DNA from a few European hunter-gatherers one must keep in mind the limitations of the scope of sampling so few to infer about so many. Though the number here is far larger (N >20 or >40 depending on the SNP), the set of markers examined was much smaller, a few pigmentation loci and mtDNA. Nevertheless this is not a trivial geographic example, nor is the time frame, from the Early Eneolithic down to the Bronze Age.

Figure S1

Figure S1

The clearest illustration of the topline result is found in the supplements (I prefer figures to tables obviously). What you see here is that there is a large difference in allele frequencies between ancient samples and modern ones from the equivalent geographic region at specific markers diagnostic for variation in pigmentation in modern Europeans. HERC2 is well known for being one of the two loci which span a long haplotype strongly correlated with blue eyes in Europeans. SLC452 and TRY are part of the standard suite of pigmentation genes which show up as variable across Eurasia. I am confused as to why they did not focus on SLC24A5, a locus which is nearly totally fixed in modern Europeans for the A allele, but may not have been so in hunter-gatherers. But in any case the result is rather clear: the ancient populations sampled here are statistically differentiated from modern populations in the same region, and, seem to have been darkly complected in comparison. The natural inference then is that powerful sweeps of natural selection increased the allele frequencies of lightening alleles in Europeans within the last ~4,000-6,000 years. This is not a crazy proposition; tests for recent natural selection in Europeans are often enriched around pigmentation loci, which are genomically atypical (long homogeneous blocks are common). What this study does is intersect inferences from modern variation with the distribution of variants in an ancient population presumed to be ancestral.

The problem of course is whether these are truly ancestral. But recall I stated earlier that they had mtDNA. This is copious, and so rather easy (comparatively!) to get from ancient DNA. Comparing their samples with modern ones from the region they find there isn’t great discontinuity. Using a model of genetic drift they support the scenario of continuity, and that the F st of ~0.005 is what you would expect for a set of populations ~4,000-6,000 years in the past. To put this in perspective this is about the Fst using autosomal SNPs between Russsians and French, or Palestinians and Greeks. Considering the time depth separating these putative populations I think even without their coalescent simulation models I can accept continuity of mtDNA intuitively. Of course the key is to not forget this is mtDNA, only the maternal lineage. If you looked at modern South Asians you’d see they’re mostly not West Eurasian. But if you looked at their Y chromosomes they’d be mostly West Eurasian. The autosomal DNA gives a half & half picture. The issue of sex mediated gene flow is made even more stark in the case of Latin America.

k8488 A model like is made more plausible by the fact that many of these individuals were of the Yamna culture, Kurgans. The thesis forwarded by some scholars is that it is these Kurgans, a patriarchal nomadic society, who brought Indo-European languages to central and western Europe ~5,000 years ago (their eastern cousins becoming Tocharians and Indo-Iranians, their southern ones Hittites and perhaps Armenians). Probably the best recent outline of this thesis is by David Anthony in The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World. I found it so engrossing that I finished it in one sitting in 2008. If these data are correct the Kurgans did not look like blonde Aryan Übermensch, rather, they became that (though to be fair, in this case we are talking about them becoming Slavs, who the Nazis labelled Untermensch). But one of the general assumptions about Kurgans is that they were groups of mobiles males. In that case one wouldn’t be surprised if their mtDNA tended to reflect subject peoples, while the whole genome was more mixed and cosmopolitan, reflecting their migrations.

So the crux then is whether to trust this mtDNA evidence as representative of the whole genome. If I simply had the mtDNA, along with the information about provenance in terms of time and place, I’d probably accept the argument for continuity. But the phenotypic markers are so different, either there’s been population replacement, or, we’ve had a lot of in situ selection. Replacement seems like the more boring hypothesis, especially in light of the fact that many of the sites sampled were not in classically Slav zones of habitation, but were occupied by Iranian or Uralic peoples, or more recently Turks. Though the researchers are using contemporary East Slavs to compare to the ancient samples, across many of these sites Slavs only become dominant in the area with the rollback of the Ottomans in the 18th century.

Ultimately I’m very unsure that the assumption of genetic continuity in this case will hold, so let’s simply take that as a given for now. Then what? You have lots of selection. The question naturally moves to why. What drove the selection? In the discussion the authors the go over many of the hypotheses rather thoroughly. Roughly they fall into two classes, the ecological/environmental and the social/sexual. The former generally has do with a combination of a switch to agriculture and the need to synthesize vitamin D due to the shift away from fish in the far north. The latter focuses on sexual selection, and favoring particular markers due to heightened paternity certainty. In particular the sexual selection hypothesis would seem to be able to explain the rise of HERC2, which is associated with light eyes, as that may be a favored trait. The immediate rejoinder is provided in the text: many of the pigmentation loci have pleiotropic effects. In other words, they tune overall pigmentation, skin, hair, and eyes, though perhaps to different extents. So if the selection was environmental due to skin it would not be totally surprising if hair and eyes changed as a side effect. Of course, as suggested in the comments here one need not posit that there was one singular selection event, as opposed to a sequential composite. Perhaps it was both environmental and sexual selection?

This again is another area where I’ll throw my hands up the air. If selection is the answer, and not population replacement, then it’s very strong. It seems that these loci were subject to sweeps in the same range of power as that around LCT, for lactase persistence, the Tibetan high altitude adaptations, as well as the various malaria resistance alleles (which have different selective dynamics, some of them balancing). One can actually still detect differential fitness at high altitudes based on phenotype, and the same with malaria, at least before modern medicine. The problem I have is that I’m just not aware of studies on the extent of differential fitness in human populations due to sexual selection. In theory sexual selection is very powerful, especially in contexts of hyper-polygyny, but to have it be realized in humans would require very particular social structures. The environmental selection arguments by their nature tend to be simpler, and therefore more attractive. But we’ve reached a point where there’s a lot of confusing stuff coming out of ancient DNA, and we need to go back to first principles, and reexamine everything. This includes sexual selection, as more than simply a deus ex machina to throw out there when we don’t have a better model on hand. That necessitates a serious examination of patterns of variance in reproductive output by phenotype, and plugging these back into models of selective sweeps.

Citation: Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 years

Note: Yulia Tymoshenko has very dark eyes. So I assume she’s not a natural blonde.

 
Hide 11 CommentsLeave a Comment
Commenters to Ignore...to FollowEndorsed Only
Trim Comments?
  1. Off-topic: Yulia’s daughter was in my class and I remember she was a very statuesque lithe blonde, easily the most eye-catching girl in the class visually.

  2. Dark eyed blond people are pretty common in Ukraine.

  3. Dark eyed blond people are pretty common in my family. But the pretty blond hair turns brown with age and the women dye it, just as Yulia has, look at her eyebrows.

  4. Dave
    Thanks for that clarification. In fact I had noticed in recent pictures of Julia that the bottom hair was brown and the braids still blond.
    To explain why this happens is a question that seems to relate to Razib’s discussion. Is the blonding genetic? Then why does it first turn brown and then grey? Is it only during child bearing age? Etc.

  5. To get an idea of the pigmentation of early people from this area, I looked at the percentages of these three genes in ALFRED. Some populations in North Africa and Pakistan have the same percentages for two of the genes as the ancient Ukranians , but they had more of the derived TYR gene. The only population with about the same percentages of all three genes as the ancient Ukranians seem to be the Mayan people from Mexico who generally have brown skin with dark eyes and hair. Obviously , pigmentation has changed a lot in South East Europe in 5000 years. I wonder if there is a parallel with Oceania where Polynesians are lighter than the Melanesians they are derived from.

  6. than the Melanesians they are derived from.

    polynesians have a minority melanesian admixture, but they are mostly derived from SE asian populations with roots in taiwan.


    To explain why this happens is a question that seems to relate to Razib’s discussion. Is the blonding genetic? Then why does it first turn brown and then grey?

    pigmentation changes over lifetime. ppl tend to get darker as they age. many ppl blonde at 5 are not at 15, and many ppl blonde at 15 are not as 35.

  7. Blond hair color is strongly affected by testosterone over time. Both male and female blonds tend to darken with age, but males more so. It is very rare to see a middle aged man with the same color blond hair he had as a child or even a teenager. Most are a light brown color by age 40. Women darken with age too, but they are more likely to ‘enhance’ their blonde color!

  8. With regard to the strength of the selective effect, it is useful to compare the selective strength of the lactase persistance gene (0.008-0.018), with the one quoted by the study assuming that selection has happened continuously from the date of the remains to the present (0.02-0.10).

    Moreover, Dienekes notes that classical Greek sources regarding the very light complexioned Indo-Iranian Scythian people in this region, who were recent arrivals as of the 8th century BCE, suggests, at a minimum, that all of the phenotypic shift took place between the date of the remains to about 2800 BCE (less than half the time period). With that timing assumption, the selection strength would be (0.04-0.20), i.e. five to ten times as strong as for LP.

    There is very good evidence to suggest that a light complexion has an intrinsic biological benefit at high latitudes where sunlight exposure is less intense (allowing for better Vitamin D production in a context where skin cancer isn’t as big a concern, etc.)

    But, the notion that a lighter complexion could have that intense of an intrinsic biological advantage between the early Bronze age and the early Iron Age in that part of Europe is profoundly implausible. Complexion ought to be more weakly selected for than LP in any case. And the location and timing (right around the time of Indo-European expansion at the geographic epicenter of the place where that occurred) provide a very plausible alternative explanation for a major, male dominated population genetic shift in the region as the original post notes.

  9. Looking at the eyebrows to determine natural hair color doesn’t work. My Dad’s eyebrows have always been darker than his hair. When he was younger, his roots came in chestnut and then people like me accused him of getting in a fight with a bottle of bleach when he was in need of a haircut. My Dad’s hair began to gray at 60, five years later he still doesn’t have true gray hair.

    My Dad does have brown eyes, tans at the sight of sun and white blond hair on his arms.

    He never put blond streaks in his hair. So far, DNA doesn’t account for the fact that some of us have hair that gets lighter from the sun and doesn’t have the ability to hold pigment.

    And as to eyebrows with women that have dirty blond eyebrows and white blond streaks. Often, we darken them. I do. Even if it is just vaseline. My eyebrow hair is lighter than my Dad’s and I want to look like I have eyebrows. And as to other areas of detection, my under arm hair is red. My uncles have red beards and dirty blond hair with white blond streaks.

  10. Yulia Tymoshenko’s real name is Yulia Abramovych Hrihyan. She likes to wear traditional Ukrainian clothes and fake hair.

  11. @ohwilleke: all of the phenotypic shift took place between the date of the remains to about 2800 BCE (less than half the time period)

    The data makes it clear that the phenotypic shift was well underway at the date of the earliest samples, and the authors suggest “the selection pressures that initiated the selective sweep during
    the Late Pleistocene or early Holocene were still operative”… so we’re talking about the tail end (or 2nd half) of a process that took maybe 10,000 years.

Comments are closed.

Subscribe to All Razib Khan Comments via RSS