Portrait of Henriette-Marie de Buade-Frontenac, Claude Mellan (1640). Curly European hair isn’t a
holdover from Africa. Europeans initially had the thick, straight, black hair
of East Asians. They then evolved thinner hair with curly, wavy, and straight
forms, and equally diverse colors.
Today,
head hair is straight in ~45% of Europeans, wavy in ~40%, and curly in ~15%
(Medland et al. 2009). As with hair and eye color, this is an unusual level of
diversity for a population that is, overall, less genetically diverse than humans
in general.
Straight
hair is produced by different genetic pathways in Europeans and East Asians,
being due to a derived EDAR allele in
East Asians and to derived TCHH, WNT10A, and FRAS1 alleles in Europeans (Medland et al. 2009; Pospiech et al
2015; Tan et al. 2013). Many other alleles are likely involved (Liu et al.
2018). At first, it was thought that hair became straight in the two groups
independently of each other, i.e., through convergent evolution, but ancient
DNA now suggests a different scenario:
1.
In a population ancestral to Europeans and to East Asians, hair became thick,
straight, and long some 30,000 years ago via a derived allele at the EDAR gene (Kamberov et al. 2013).
2.
This ancestral Eurasian population differentiated into a western group that would
become Europeans and an eastern group that would become East Asians (Rogers
1986).
3.
Thick straight hair remained prevalent in the eastern group and gradually
disappeared in the western group. Nonetheless, as late as eight thousand years
ago it still prevailed in half of Europeans, as shown by ancient DNA retrieved
from Motala, Sweden (Mathieson et al. 2015). Today, it has an incidence of 87%
in Asians and about 1% in Europeans (McVean et al. 2012; Unterländer et al.
2017).
4.
In early Europeans, thick straight hair was apparently replaced by thinner hair
with diverse forms ranging from curly to straight. Curly European hair is thus
a derived trait, and not a holdover from ancestral Africans.
This
diversification must have coincided temporally and geographically with
diversification of hair and eye color, and the cause was probably the same:
sexual selection of women by men in a mate market with too many unmated women.
If the selection pressure is strong enough, preferences for novel visual
stimuli become decisive in mate choice (Frost 2006; Frost 2014). This kind of
preference was observed in a Viennese study, which found that women tend to
change their hair form to less common types (Schweder 1994).
As
with hair and eye color, hair form seems to have diversified in response to a stronger
selection pressure than the one that caused hair to lengthen at an earlier date
in ancestral Eurasians.
References
Frost,
P. (2006). European hair and eye color - A case of frequency-dependent sexual
selection? Evolution and Human Behavior
27(2): 85-103.
Frost,
P. (2014). The puzzle of European hair, eye, and skin color. Advances in Anthropology 4(2): 78-88.
Kamberov,
Y.G., S. Wang, J. Tan, P. Gerbault, A. Wark, L. Tan, et al. (2013). Modeling
Recent Human Evolution in Mice by Expression of a Selected EDAR Variant. Cell 152(4): 691-702.
Liu,
F., Y. Chen, G. Zhu, P.G. Hysi, S. Wu, K. Adhikari. (2018). Meta-analysis of
genome-wide association studies identifies 8 novel loci involved in shape
variation of human head hair. Human Molecular
Genetics 27(3): 559-575.
Mathieson,
I, I. Lazaridis, N. Rohland, S. Mallick, N. Patterson, S. Alpaslan, et al.
(2015). Genome-wide patterns of selection in 230 ancient Eurasians. Nature 528(7583): 499-503
McVean,
G.A. et al. (The 1000 Genomes Project Consortium) (2012) An integrated map of
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Medland,
S.E., D.R. Nyholt, J.N. Painter, B.P. McEvoy, A.F. McRae, G. Zhu, et al.
(2009). Common variants in the Trichohyalin gene are associated with straight
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R. A. (1986). Language, human subspeciation, and ice age barriers in Northern
Siberia. Canadian Journalof Anthropology
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B.I.M. (1994). The impact of the face on long-term human relationships. Homo 45(1): 74-93.
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J., Y. Yang, K. Tang, P.C. Sabeti, L. Jin, and S. Wang. (2013). The adaptive
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Unterländer,
M., F. Palstra, I. Lazaridis, A. Pilipenko, Z. Hofmanová, M. Gross, et al.
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