Tătăroaice – Petre Iorgulescu-Yor (source). Today, the steppes north of the Black Sea lie within the European world—politically, culturally, and demographically. Not so long ago, they were home to nomads of Central Asian origin.
A new study shows that Europeans underwent strong selection for white skin, non-brown eyes, and non-black hair … during historic times!
Here we present direct estimates of selection acting on functional alleles in three key genes known to be involved in human pigmentation pathways—HERC2, SLC45A2, and TYR—using allele frequency estimates from Eneolithic, Bronze Age, and modern Eastern European samples and forward simulations. Neutrality was overwhelmingly rejected for all alleles studied, with point estimates of selection ranging from around 2-10% per generation. Our results provide direct evidence that strong selection favoring lighter skin, hair, and eye pigmentation has been operating in European populations over the last 5,000 y.(Wilde et al., 2014)
If true, this finding would contradict other recent findings. Two studies have found a much earlier time frame for the whitening of European skin: 11,000 to 19,000 years ago (Beleza et al., 2013) and 7,600 to 19,200 years ago (Canfield et al., 2014). Two studies of ancient DNA indicate that non-brown eyes were already in existence 7,000 years ago in Spain (Olalde et al., 2014) and 8,000 years ago in Luxembourg (Lazaridis et al., 2013). Moreover, the genes responsible are the same as the ones in above quote.
So who is right and who is wrong? All of these studies are probably right, but only for some early Europeans and not for all. In the latest study, the samples come from a very small part of Europe—the steppes north of the Black Sea:2
Ancient DNA was retrieved from 63 out of 150 Eneolithic (ca. 6,500-5,000 y ago) and Bronze Age (ca. 5,000-4,000 y ago) samples from the Pontic-Caspian steppe, mainly from modern-day Ukraine. […] We also genotyped the three pigmentation-associated SNPs in a sample of 60 modern Ukrainians (28) and observed an increase in frequency of all derived alleles between the ancient and modern samples from the same geographic region (Table 1 and Fig. S1). This implies that the pigmentation of the prehistoric population is likely to have differed from that of modern humans living in the same area.
[…] Inferring natural selection based on temporal differences in allele frequency requires the assumption of population continuity. To this end we compared the 60 mtDNA HVR1 sequences obtained from our ancient sample to 246 homologous modern sequences (29–31) from the same geographic region and found low genetic differentiation (FST = 0.00551; P= 0.0663) (32). Coalescent simulations based on the mtDNA data, accommodating uncertainty in the ancient sample age, failed to reject population continuity under a wide range of assumed ancestral population size combinations. (Wilde et al., 2014)
The authors are placing the burden of proof on the wrong null hypothesis when they state that their simulations “failed to reject population continuity.” The null hypothesis should be population discontinuity. For example, Swedes and Greeks differ in skin tone and eye color, and if we compare their autosomal DNA we get a comparable FST of 0.0084 (Genetic History of Europe, 2014). Admittedly, FST is different with mitochondrial DNA.
I suspect the authors ruled out population discontinuity because their FSTseemed incompatible with a non-European population giving way to a European one. If so, they forgot one thing. They were comparing a population of the present with one that existed some 5,000 years ago. If you go farther and farther back in time, any human population will look more and more ancestral to a present-day population. This is especially so in northern Eurasia, where a population ancestral to both Europeans and Amerindians existed some 20,000 years ago. Yes, the FSTdoes seem incompatible with a non-European population giving way to a European one, but this is because the ancient DNA comes from a non-European population that was closer to the time of common origin for all northern Eurasians.
This ancient DNA may come from a mixed European/Central Asian population or an intermediate and now extinct population, perhaps similar to the Lapps. If we look at the derived (European) alleles for the three genes in question (HERC2, SLC45A2, TYR), the frequencies fall halfway between those of Europeans and Asians (see Table 1 in the paper). In any case, this population does not have to be of non-European origin to be noticeably darker in skin color. As shown by the recent Mesolithic findings from Luxembourg and Spain, there used to be apparently native dark-skinned populations in the heart of Europe.
Historical background
The hypothesis of population discontinuity becomes even more plausible if we look at the history of this region. Today, the steppes north of the Black Sea lie within the European world—politically, culturally, and demographically. Not so long ago, they were home to nomads of Central Asian origin. The latest of them, the Tatars, held sway until the 18th century.
The Tatars intermixed extensively with Slavic wives and concubines, so much so that they now look almost as fair as other Europeans. But they were originally quite swarthy, as attested by medieval sources. In a 14th-century romance, The King of Tars, a Tatar Khan converts to Christianity and turns white in the baptismal water. Two other chronicles of the same period describe how a Tatar Khan's Christian concubine bears him a son white on one side and black on the other. When baptized, the child emerges from the water white on both sides (Hornstein, 1941; Metlitzki, 1977, p. 137).
Medieval writers often noticed this difference in skin color. Genoese notaries usually described Tatar slaves as olive-skinned (Plazolles Guillen, 2012, p. 119). Florentine acts of sale give the following numerical breakdown of Tatar slaves by skin color: black 2, brown 18, olive 161, fair 11, reddish 5, white 45 (Epstein, 2001, p. 108). During a trial, a slave tried to regain her freedom by claiming to be Russian and, hence, Christian. Her owner rebuked her, saying: “You’ve lied to me. You look more like a Tatar, not at all like a Russian” (Plazolles Guillen, 2012, p. 119).
The Tatars were preceded by other nomads of Central Asian origin. The Scythians (8th to 2nd century BC) were likewise described as dark-skinned. Hippocrates wrote: “The Scythian race are tawny from the cold, and not from the intense heat of the sun, for the whiteness of the skin is parched by the cold, and becomes tawny” (Hippocrates).
One can find references to the contrary (Scythians, 2014). Keep in mind that the word “Scythian” was often used in the ancient world to encompass all northern peoples:
To the ancient Greeks the Scythians, Sarmatians, Germans, and Goths were the remote northern races of antiquity. Geographically near to one another, they were often grouped together under the term “Scythians,” which by the third century B.C.E. no longer had an ethnic or national connotation and had come to designate the peoples of the remote north.(Goldenberg, 2003, p. 43)
The term “Scythian” may also have subsumed different peoples north of the Black Sea, some of whom came from Central Asia and others from areas farther north and west.
Conclusion
Because this region is on the periphery of the European world and has been exposed to migrations from Central Asia, population change is a likelier explanation for the findings of Wilde et al.
These findings are nonetheless interesting. Together with the ancient DNA from Mesolithic hunter-gathers in Spain and Luxembourg, we have further proof that many early Europeans were brown-skinned. Indeed, this seems to have been the physical appearance of all Europeans during their first 20,000 years in Europe. Only later, within the time frame of 20,000 to 10,000 years ago, did some of them become white.
This may seem surprising to those who believe that white skin is an adaptation to weak sunlight at high latitudes. It was thought that Europeans became white because their ancestors no longer needed dark pigmentation to protect themselves against sunburn and skin cancer. Meanwhile, light pigmentation became necessary to maintain synthesis of vitamin D. There was admittedly the example of dark-skinned peoples who have long lived at similar latitudes in Asia and North America, but that counterfactual was attributed to the availability of vitamin D from a marine diet, such as among the Inuit of northern Canada.
Wilkes et al. do, in fact, address the apparent contradiction between their findings and the hypothesis that ancestral Europeans became white to maintain adequate production of vitamin D in their skin. In their Discussion section, they suggest that the shift from hunting and gathering to farming led to a decrease in dietary vitamin D (from fatty fish and animal liver). The main problem with this explanation is that farming came late to many parts of Europe: about 2,000 to 3,000 years ago for East Baltic peoples and less than 3,000 years ago for Finnish peoples (and incompletely at that). This leaves a very narrow time frame for evolution from brown skin to white skin. Ultimately, this question will be resolved with retrieval of ancient DNA from these populations.Notes
1. Although Wilde et al. mention hair color, they did not study the main hair-color gene, MC1R.
2. Razib Khan has a great map of the ancient DNA samples.
References
Beleza, S., Murias dos Santos, A., McEvoy, B., Alves, I., Martinho, C., Cameron, E., Shriver, M.D., Parra E.J., and Rocha, J. (2013). The timing of pigmentation lightening in Europeans. Molecular Biology and Evolution, 30, 24-35.
http://mbe.oxfordjournals.org/content/30/1/24.shortCanfield, V.A., A. Berg, S. Peckins, S.M. Wentzel, K.C. Ang, S. Oppenheimer, and K.C. Cheng. (2014). Molecular phylogeography of a human autosomal skin color locus under natural selection, G3, 3, 2059-2067.
http://www.g3journal.org/content/3/11/2059.full Epstein, S.A. (2001). Speaking of Slavery. Color, Ethnicity, & Human Bondage in Italy, Ithaca: Cornell University Press.
Genetic History of Europe. (2014). Wikipedia
http://en.wikipedia.org/wiki/Genetic_history_of_Europe Goldenberg, D.M. (2003). The Curse of Ham. Race and Slavery in early Judaism, Christianity, and Islam, Princeton: Princeton University Press.
Hippocates. On Airs, Waters, and Places, part 20. Translated by Francis Adams
http://classics.mit.edu/Hippocrates/airwatpl.20.20.htmlHornstein, L.H. (1941). New analogues to the King of Tars, Modern Language Review, 36, 433-442.
Khan, R. (2014). Descent and selection is a bugger: Black Kurgans, March 12, The Unz Review: An Alternative Media Selection
http://www.unz.com/gnxp/descent-and-selection-is-a-bugger/Lazaridis, I., Patterson, N., Mittnik, A., Renaud, G., Mallick, S., et al. (2013). Ancient human genomes suggest three ancestral populations for present-day Europeans, BioRxiv, December 23.
http://biorxiv.org/content/early/2013/12/23/001552.full-text.pdf+html Metlitzki, D. (1977). The Matter of Araby in Medieval England, New Haven and London, Yale University Press.
Olalde, I., M.E. Allentoft, F. Sanchez-Quinto, G. Saintpere, C.W.K. Chiang, et al. (2014). Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European, Nature, early view
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12960.html Plazolles Guillen, F. (2012). “Negre e de terra de negres infels …”: Servitude de la couleur (Valence, 1479-1516), in R. Botte and A. Stella (eds.) Couleurs de l’esclavage sur les deux rives de la Méditerranée (Moyen Âge – xxe siècle), pp. 113-158, Paris: Karthala.
Scythians. (2014). Wikipedia
http://en.wikipedia.org/wiki/Scythians Wilde, S., A. Timpson, K. Kirsanow, E. Kaiser, M. Kayser, M. Unterländer, N. Hollfelder, I.D. Potekhina, W. Schier, M.G. Thomas, and J. Burger. (2014). Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 y, Proceedings of the National Academy of Sciences, published ahead of print.
http://www.pnas.org/content/early/2014/03/05/1316513111.full.pdf+html