Selection for fair skin in Europeans and North Asians

 

Selection for fair skin in different human populations (Huang et al. 2021)

Selection for fair skin was about four times stronger among ancestral Europeans than it was among ancestral North Asians or the earlier shared ancestors of both groups. So says a recent genome study.

 

Huang et al. (2021) examined genes that influence skin pigmentation to calculate the strength of selection for lighter skin among the ancestors of today’s Europeans and North Asians. They concluded that selection for lighter skin was strongest among the unique ancestors of present-day Europeans, with a selection pressure of 25.9. It was about four times weaker among the unique ancestors of North Asians (5.61) and the earlier shared ancestors of both groups (6.5). East Asians actually became darker after they split from North Asians, with a negative selection pressure of -5.53.

 

Our estimate shows that the modern European lineage had the largest selective pressure (s4=0.0259/generation) on light pigmentation than the other branches, suggesting that recent natural selection favoured light pigmentation in Europeans. Recent studies using ancient DNA could support our observation of recent directional selection in Europeans (Huang et al. 2021, p. 3)

 

This finding supports earlier findings. Modern humans remained dark-skinned in Europe long after they had spread north into northern latitudes some 45,000 years ago. It was not until 20,000 years ago that alleles for white skin made their appearance (Beleza et al. 2013; Canfield et al. 2014; Norton and Hammer 2007). As a Science correspondent concluded: "The implication is that our European ancestors were brown-skinned for tens of thousands of years" (Gibbons 2007).

 

Those ancestors were initially proto-Eurasians, and it was only later that they differentiated to become respectively Europeans and North Asians. Only then, and only in the European lineage, did skin color begin to lighten at a fast rate. This rapid evolution seems to have been confined to a relatively small area that stretched from the Baltic to central Siberia. Elsewhere, in western and southern Europe, people remained dark-skinned until almost the dawn of history, as shown by DNA dated to 11,000 years ago from England, 8,000 years ago from Luxembourg, and 7,000 years ago from Spain (Brace et al. 2019; Lazaridis et al. 2014; Olalde et al. 2014).

 

The fair skin phenotype, together with a variety of hair and eye colors, would later spread throughout all of Europe, while going extinct east of the Urals. In the latter region it would persist into historic times. At sites in south-central Siberia, dating from the third millennium BC to the fourth century AD, genetic analysis has shown that most of the buried individuals had blue or green eyes, light hair (blond, red, light brown), and light skin (Bouakaze et al. 2009). South Siberian peoples were, in fact, described as having "green eyes" and "red hair" in old Chinese records (Keane 1886, p. 703).

 

It seems that Europeans acquired their current appearance very fast, perhaps ten to twenty thousand years ago during the last ice age. Initially confined to northeastern Europe and parts of Siberia, the new phenotype would in time spread to the rest of the continent ... on the eve of recorded history. Only then did all Europeans come to look “European” (Frost 2014; Frost 2020).

 

References

 

Beleza, S., A.M. Santos, B. McEvoy, I. Alves, C. Martinho, E. Cameron, et al. (2013). The timing of pigmentation lightening in Europeans. Molecular Biology and Evolution 30(1): 24-35. https://doi.org/10.1093/molbev/mss207

 

Bouakaze, C., C. Keyser, E. Crubézy, D. Montagnon, and B. Ludes. (2009). Pigment phenotype and biogeographical ancestry from ancient skeletal remains: inferences from multiplexed autosomal SNP analysis. International Journal of Legal Medicine 123(4): 315-325.

https://doi.org/10.1007/s00414-009-0348-5

 

Brace, S., Y. Diekmann, T.J. Booth, Z. Faltyskova, N. Rohland, S. Mallick, et al. (2019). Ancient genomes indicate population replacement in Early Neolithic Britain. Nature Ecology & Evolution 3(5): 765-771. https://doi.org/10.1038/s41559-019-0871-9

 

Canfield, 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(11): 2059-2067. https://doi.org/10.1534/g3.113.007484

 

Frost, P. (2014). The puzzle of European hair, eye, and skin color. Advances in Anthropology 4(2): 78-88. http://www.scirp.org/journal/PaperInformation.aspx?PaperID=46104

 

Frost, P. (2020). White Skin Privilege: Modern Myth, Forgotten Past. Evolutionary Studies in Imaginative Culture 4(2): 63-82. https://doi.org/10.26613/esic/4.2.190

https://www.jstor.org/stable/10.26613/esic.4.2.190

 

Gibbons, A. (2007). American Association of Physical Anthropologists Meeting: European skin turned pale only recently, gene suggests. Science 20 April 2007, 316(5823): 364.

https://doi.org/10.1126/science.316.5823.364a

 

Huang, X., S. Wang, L. Jin, and Y. He. (2021). Dissecting dynamics and differences of selective pressures in the evolution of human pigmentation. Biology Open 15 February 2021; 10(2): bio056523. https://doi.org/10.1242/bio.056523

 

Keane, A.H. (1886). Asia with Ethnological Appendix. London: Edward Stanford.

 

Lazaridis, I., N. Patterson, A. Mittnik, G. Renaud, S. Mallick, K. Kirsanow, et al. (2014). Ancient human genomes suggest three ancestral populations for present-day Europeans. Nature 513(7518): 409-413. https://doi.org/10.1038/nature13673

 

Norton, H.L., and M.F. Hammer. (2007). Sequence variation in the pigmentation candidate gene SLC24A5 and evidence for independent evolution of light skin in European and East Asian populations. Program of the 77th Annual Meeting of the American Association of Physical Anthropologists, p. 179.

 

Olalde, I., M.E. Allentoft, F. Sanchez-Quinto, G. Santpere, C.W.K. Chiang, M. DeGiorgio, et al. (2014). Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European. Nature 507 (7491): 225-228. https://doi.org/10.1038/nature12960