Yann commented on a new paper, Association of the SLC45A2 gene with physiological human hair colour variation:
Pigmentation is a complex physical trait with multiple genes involved. Several genes have already been associated with natural differences in human pigmentation. The SLC45A2 gene encoding a transporter protein involved in melanin synthesis is considered to be one of the most important genes affecting human pigmentation. Here we present results of an association study conducted on a population of European origin, where the relationship between two non-synonymous polymorphisms in the SLC45A2 gene -- rs26722 (E272K) and rs16891982 (L374F) -- and different pigmentation traits was examined. The study revealed a significant association between both variable sites and normal variation in hair colour. Only L374F remained significantly associated with hair colour when both SNPs were included in a logistic regression model. No association with other pigmentation traits was detected in this population sample. Our results indicate that the rare allele L374 significantly increases the possibility of having black hair colour (OR = 7.05) and thus may be considered as a future marker for black hair colour prediction.
Photo credit: John Donegan
Other SNPs at this locus have been associated with skin color variation. But this is looking at a Polish population. Other studies looked at a more diverse array of populations. Also, I know some people will attribute the existence of darker-skinned Poles to the influx of Tatars from the east. First, I'm generally skeptical of this argument because it doesn't seem like they were numerically very significant. After all, it is difficult (though not impossible) to detect the historically much more significant Magyar and Turkic settlement within the boundaries of modern Hungary via genetic techniques. Most of the inhabitants of Hungary seem to be not too dissimilar genetically from their neighbors. Secondly, this locus seems to have been subject to a selective sweep relatively recently:
The maximum-likelihood estimate of t is 10,965 years. Ninety-five percent confidence intervals for this age can be...This produces the values...1,328 and...39,609 years.
In other words, the ancestral variant of SLC45A2 in the Polish population may be indigenous to the Polish population, and not due to exogenous genetic inputs within the last few thousand years. Unlike at SLC24A5 Europeans are not totally fixed for the derived variant. A closer look at the pattern of variation around this locus on individuals who carry the ancestral allele of SLC45A2 in Poles could probably answer this narrow question.*
Below the fold is a Google Map from ALFRED which plots the frequencies of the two alleles in the SNP implicated in black hair prediction in this study:
Related: Other posts mentioning this locus....
Postscript: Poland has 15-50,000 Roma ("Gypsies"). This is probably an underestimate, and there is a fair amount of admixture between Roma and their host populations. Because the host are much more numerous the impact on the Roma is more significant, but it seems more likely that if Marzena Cielik's appearance is due to recent exogenous genetic input it is Roma rather than Tatar (H/T to the spammer/troll "Levi Johnston," who put it a bit more crudely).
* Also, as in much of eastern Europe immigrant Turks were a warrior caste who were generally assimilated into the nobility. So if there are differences in complexion by class origin, that might be indicative of a large genetic input.
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I'm confused a bit by this map. I take it that blue is the "black hair" allele, and that it is also the ancestral allele. Which makes yellow the derived allele. I see the UK, and I realize that the derived allele is nearly fixed in Scotland and Britain. But those places have a huge proportion of black-haired people. So that means there are two different black-hair genes bouncing around Europe? Very interesting. Also, I assume, one copy of the black-hair gene is enough to produce the phenotype, right?
this is a specific case where allele X against genetic background Y can predict a particular proportion of a phenotype Y. remember the definition for heritability: it's explaining the proportion of phenotypic variation attributable to genetic variation. so there isn't a *necessary* connection between this allele and black hair, though there is somewhat a *sufficient* one (in this population context).
IOW, there are almost certainly other ways to get very dark hair.
Damn, someone beat me to the Gypsy angle! I seriously thought you'd caved and finally posted a picture of a Brown babe.
But yeah, we don't need the "imported" hypothesis to account for why people aren't all the same in a population. Frequency dependence! Pigmentation is associated with behavior -- darker types being more aggressive and more sexual. In a frequency dependent scenario, some fraction of Poles will pursue a more domesticated strategy (and have light hair), while others will be more wild (and have dark hair).
Same for elsewhere, the equilibrium fractions being determined by "the ecology" -- like pathogen load, which is higher in Poland than England, with more bugs leading to higher payoffs for the more promiscuous strategy (maximizing diversity of offspring, etc.).
"Come on Genghis, we only need one more to make up a horde"
I have read that the Mongols forced the Polish peasants to sow for them, therefore they spent a year there. What did they do to while away the evenings; all very consensual of course.
However you are undoubtedly correct that the dark haired gene is native to Poland. My understanding of Peter Frost's work is that he places a lot of emphasis on the negative frequency dependent selection of hair colour, I think he would be surprised if the native black hair allele was eliminated. Black haired girls would be considered "hot", where they were rare.
agnostic said
"pathogen load which is higher in Poland than England, with more bugs leading to higher payoffs for the more promiscuous strategy (maximizing diversity in offspring)"
That is the usual explaination for polygamy in Africa I believe. John Manning* takes a different veiw, he points out than some men are going to be excluded from reproduction and that the diversity of the poulation will decrease. He thinks that polygamy raises testosternisation and that this costs in terms of testosterone depressing immunity. He gives a list of tropical diseases that are more prevalent in men. The load of the River blindness parasite is greater in cases of male infection for example. He suggests polygamy is the cause of higher rates of infectious disease. The corollary of this is lower rates of atopic disease.
* The Finger Book(2008)
Pigmentation is associated with behavior -- darker types being more aggressive and more sexual. In a frequency dependent scenario, some fraction of Poles will pursue a more domesticated strategy (and have light hair), while others will be more wild (and have dark hair).
I see this assertion bandied about a bit, and I'm biased in favor of it because it conforms somewhat to my own anecdotal experiences, but what study or studies is it based on?
Also, is it just within-group variation that correlates with agression and sexuality, or is the correlation evident between groups as well? And please, don't anyone reply with data showing that white Americans are more "domesticated" than people of African descent here in the United States. It's not that those social statistics (e.g. marriage rates, incarceration rates, STD rates, etc...) aren't valid, or that I think it's impossible that they may reflect real underlying biologcal differences. It's just that I want data from more than two population groups!
"Cieslik" if you want more pictures.
Are there any studies or any more information about Roma/Gypsy admixture into the host populations?
Mutation History of the Roma/Gypsies
Origins and Divergence of the Roma (Gypsies).
these photos of prominent czech and slovak roma. some could pass as pure south asian, and some could pass as eastern european. most in the middle.
Prominent Roma would be the rom baro who deals with the gadji (non Roma)* on behalf of the community. Not looking too much like a "Gypsy" would be a asset, they may be rather untypical.
Romanian Roma are said to be genetically distictive
*gadz is a Scottish expression of great disgust, gadjies for dirty people amusingly, Dad is a originally a Romani word I believe