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
6 comments:
"East Asians actually became darker after they split from North Asians". I would have thought it unlikely that a lost character eg one of the genes for melanin, could be re-evolved. Isn't population replacement a more likely explanation? The original Great Wall of China was built to keep out the Xiong-nu, horse riding barbarians from the steppes, who were described as auburn haired. (In contrast, the Chinese called themselves the "black haired people".) The use of the horse for riding, as distinct from drawing chariots, began among white people on the Russian steppes, of which the Scythians were a good example. This would have given them the opportunity to move east and become the Xiong-nu. But eventually, the "black haired people", such as the Tatars and the the Mongols learned how to ride horses, and push the auburn haired people back where they came from.
"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)."
Where did they go?
Malcolm,
New mutations arise all the time, and not all alleles are totally lost. I don't see how population replacement could be used as an explanation for an analysis done on present-day East Asians and North Asians.
John,
Not all populations get to live forever. They went extinct.
Where is the line drawn between North Asian and East Asian people in this instance?
The two mutations that influence skin color in the most drastic way we know, one in the SLC24a5 gene and the other in the SLC45a2 gene, were already present in Anatolia, during the Neolithic period (something like 10,000 years ago). One of these mutations was also present in individuals from the Natufian culture! When Lazarids releases the 25000 yrs Dzudzuana hunter sequence, I believe it will reveal that they had at least one of these mutations. The mutation of the SLC24a5 gene appears to radiate from the Caucasus.
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