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
genetic variation from 1,092 human genomes. Nature
491: 56-65.
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
hair in Europeans. The American Journal
of Human Genetics 85(5): 750-755.
Pospiech,
E., J. Karlowska-Pik, M. Marcinska, S. Abidi, J. Dyrberg Andersen, M. van den
Berge, et al. (2015). Evaluation of the predictive capacity of DNA variants
associated with straight hair in Europeans. Forensic
Science International: Genetics 19: 280-288.
Rogers,
R. A. (1986). Language, human subspeciation, and ice age barriers in Northern
Siberia. Canadian Journalof Anthropology
5(1): 11-22.
Schweder,
B.I.M. (1994). The impact of the face on long-term human relationships. Homo 45(1): 74-93.
Tan,
J., Y. Yang, K. Tang, P.C. Sabeti, L. Jin, and S. Wang. (2013). The adaptive
variant EDARV370A is associated with straight hair in East Asians. Human Genetics 132(10): 1187-1191.
Unterländer,
M., F. Palstra, I. Lazaridis, A. Pilipenko, Z. Hofmanová, M. Gross, et al.
(2017). Ancestry and demography and descendants of Iron Age nomads of the
Eurasian Steppe. Nature
Communications 8(14615)
23 comments:
Do you suppose male pattern baldness is a side effect of this selection on hair? Or do you think there is some other explanation for MPB?
"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.
I do not suggest that it was the origin of curly hair, but the current prevalence of curly hair may stem from a third wave of extremely intense selection in the early Bronze Age.
Curly and colourful hair is commonest in Ireland (most Irish hair has a bit of curl to it) and Irish hair also has almost the highest prevalence of red hair. What rewarded the curly often colourful hair was male attraction at a time when there was a shortage of husbands, but what was this time and why are curls found so much more in Ireland more than in other places? A particularly intense androcide by a relatively small number of male invaders would explain the stronger selection for eye-catching curly hair in Ireland. You cannot get more noticeable that curly red locks. IRELAND has the highest concentration in the world of men who carry the R1b DNA marker and its sub-groups"
The extreme bottleneck of male ancestry in Ireland, and the appearance of Irish hair being so diversified converges on the conclusion that the selection was not quite so rooted in the Ice Age as previously theorized, but sexual selection is the explanation for the unique features of European appearance, as you have long said.
The proximal explanation is testosterone (DHT to be precise). One theory I want to explore is that a microbe may cause or aggravate MPB by stimulating sensitivity to DHT. In doing so, the microbe may be creating a more friendly environment for itself (more nutrients? protection from immune response?). This is one of those ideas that simmer on my back burner.
I know it sounds weird, but dermatologists once widely believed that MPB in young men is due to a scalp infection.
Anon,
It could be regional selection during the late Paleolithic/early Mesolithic. Red hair is likewise more common in Ireland and Scotland.
Anon was me. Razib Khan says of derived (white skin) SLC24A5 “there are very very very few copies of the ancestral allele across so much of europe. this seems to be a recent feature of the last 5,000 years“. There seems to be a sudden Europe-wide dearth of dark skinned people starting from the early Bronze age, and one would wonder if that was contemporaneous with an increase in the gene that produces red hair (which also confers very pale skin). Regional selection it may have been, but whenever the people who now live in Ireland developed such a lot of curly hair, there was a shortage of husbands at that time.
Peter,
Interesting theory.
I have heard that DHT stimulates oily sebum production. Sebum is produced around the base of hair follicles. In MPB, the hair follicles don't actually die, but just miniaturize to a very small size. The extra sebum at the base of the follicle may crowd out and stunt the growth of the follicle. Perhaps the microbe feeds on the excess sebum or the excess sebum is a better environment for it?
Itchiness is a very common symptom of MPB. I've noticed that in areas where my hair is receding, the hair that sheds or comes off from scratching tends to consist of very small follicles with enlarged bases that seem to be made up of sebum. This contrasts with when I was younger or with the normal parts of my scalp where the hair that sheds is longer and the base is simply the hair follicle base with no sebum.
The general treatment of MPB today consists of "the big three": a DHT inhibitor called Propecia or generically Finasteride, a hair growth stimulant called Rogaine or generically Minoxidil, and an anti-dandruff shampoo that contains ketoconazole, which is an antifungal drug. Dandruff is generally believed to be caused by some bacteria or fungi. Perhaps the antifungal properties of ketoconazole also are affecting a microbe that causes MPB?
I doubt the derived condition in Motala is from common descent with East Asians, but it does remind me of Fu and his co workers claiming an East Asian connection to Loschbour and La Brana. They don't know how that got there but not all their Villabruna cluster have it and they think it it arrived 13,000 years ago. They're a bit confusing about Motala though...
http://www.nature.com/articles/nature17993
I doubt the derived condition in Motala is from common descent with East Asians
I wonder what makes you think so, I was not aware that parallel evolution was a default assumption when the same derived gene is found in two populations. Amerindians also have derived EDAR though not at the high level of East Asians.
If straight hair remained prevalent in the eastern group and gradually disappeared in the western group then fine curly hair was selected for in the Western group. The increased prevalence of derived EDAR in east Asians as compared with Amerindians may have been the result of demographic processes in East Asians not selection. See Chang (2018). A possible additional reason for derived EDAR being selected against in the West is that it reduces mammary gland size.
@ Sean, just one mutation can appear in more than one population/location. The reason its not usual to assume parallelism when the same derived gene is found in two populations, is those populations are not usually so different as Asians/Amerinds are from Motala. That difference involves both time and space.
If Amerinds have less derived EDAR in Asians no less than three explanations might explain that. 1) the Mal'ta-Burets component already in the Paleoindians, 2) recent colonial admixture, and 3) the Andamanese-like component in Brazil.
Sean,
I really don't understand Razib's position on this. Five thousand years ago, white skin was not prevalent across all of Europe, but it was in Scandinavia and the East Baltic at least as far back as Mesolithic times.
I suspect that the high incidence of red hair and curly hair in the Celtic fringe (Ireland, Scotland) has its origins in a Doggerland population from the early Mesolithic. But that's just speculation on my part.
Anon,
I'll discuss this issue in my next post. I suspect that MPB is aggravated by a fungal pathogen (a form of yeast). Unfortunately, an infection of the hair follicle cannot be eliminated by a shampoo. I'm also wary of ketoconazole because of its toxicity.
Anon,
"The reason its not usual to assume parallelism when the same derived gene is found in two populations, is those populations are not usually so different as Asians/Amerinds are from Motala."
For Amerindians and Motala, the time to a common origin is about 8,000 to 13,000 years. That's more than enough time to produce the differences in physical appearance.
Peter,
Looking forward to your next post.
I had heard ketoconazole can be toxic when taken orally. Can it be dangerous when applied topically as well?
@Peter, my problem is that it feels less parsimonious to have a common origin when Mongoloid traits are thought to arrive in Europe thousands of years later with the Lapps. Though if what Fu said is correct I could be swayed.
Re derived EDAR, Motala in known from a tiny group of skulls that bore the hallmarks of a massacre of indigenous population by invaders.
"Re derived EDAR, Motala in known from a tiny group of skulls that bore the hallmarks of a massacre of indigenous population by invaders."
Do you suppose there are parallels with the European conquest of the Americas, which would have reduced derived EDAR prevalence in areas of significant or total replacement?
Anon,
In theory, topical treatments do not have systemic effects because the skin acts as a barrier. This barrier, however, can be compromised if the skin is infected. Twenty years ago I was prescribed a ketoconazole ointment for a seborrheic infection. After a month I began to feel sickish, and I went to see my physician, who reassured me that an ointment could not have systemic effects. I week after I became violently ill and I stopped using the ointment. I returned to normal.
Anon,
The Sami (Lapps) are better understood as an intermediate population and not as a mixed European/East Asian population. Gene flow from East Asia has occurred at different times, e.g., the Huns, the Golden Horde, etc.
Sean,
A massacre? No. They seem to have been buried as part of an elaborate ceremony:
"Archaeological excavations in 2009-2011 at Kanaljorden in the town of Motala, Ostergotland
in central Sweden have unearthed a complexMesolithic site with ceremonial depositions
of human crania in a former lake. The human skulls have been treated in a complex ceremony that involved the display of skulls on stakes and the deposition of skulls in water. The
rituals were conducted on a massive stone packing (14 x 14 m) constructed on the
bottom of the shallow lake."
http://www.academia.edu/3122672/Mesolithic_skull_depositions_at_Kanaljorden_Motala_Sweden
@Peter, I disagree re: the Lapps, because they seem pretty obviously European Hunter Gatherer save for the slight East Asian admixture they possess: they must be hybrids but predominand Caucasian of Mesolithic origins. People forget how late the Lappish migration to the Arctic was - the Kjelmöy Ware is the most plausible candidate.
Anony, you could know a population of dogs originated when bloodhounds and greyhounds interbred in equal numbers, but if you could see the hybrids generation later were long eared and had their heads down sniffing the ground all the time, you would know they had not been selected for catching rabbits. Modern Swedes don't have the straight thick hair (and small mammary glands) of derived EDAR, because it was selected against. To me, determining what the admixture originally was is a side issue, the interesting thing is how the selection worked.
Peter, "HALGREN also explained that most examples of this practice pertain to the historic period, in which colonial representatives mounted the skulls of murdered natives on wooden stakes."
Mesolithic head cults sounds like Ofnetholen, and Motala plots close to Ofnet in Fu's scattergram.
Mmm... https://www.researchgate.net/publication/275542043_Mesolithic_%27skull_cults%27
"One suggestion for the evidence of cutmarks, defleshing and dismemberment is that it relates to preparation of the body for transport to an appropriate burial location by mobile hunter-gatherers (Haverkort & Lubell 1999), an argument that has also been made in relation to secondary burial and ‘skull’ removal in the Natufian (Hershkovitz & Go-pher 1990)."
"While ‘skull cups’ do not appear to feature in the Mesolithic, other practices involving crania are reminiscent of those seen in the Late Upper Palaeolithic (this need not imply any direct continuity of the tradition, nor uniformity of meaning)."
"Cutmarks consistent with scalping have also been noted on Late Mesolithic remains, including a child’s cranium from Dyrholmen (Jutland, Denmark) as well as examples from Ålekistebro (Sjælland, Denmark) and Drigge (Rügen, Germany) (Brinch Petersen 2006; Degerbøl 1942; Terberger 1998). Probable cases of scalping that have survived have been found at Skateholm in southern Sweden (Ahlström 2008) and Zvejnieki in Latvia (Jankauskas 2012). Presumably most or all of these examples relate to trophy taking, as the hair is widely believed cross-culturally to be a powerful bodily substance."
"The issue of differentiating between a ‘venerated ancestor’ and a trophy head is not seen as problematic in itself (though identifying which is in play in any particular instance of course remains difficult), since they can be in-terpreted as two sides of the same coin, an outcome of the belief that the head holds or concentrates the life force (Hoskins 1989, 1996a, 1996b). The ways in which this is harnessed are diverse, but often involve corporeal re-mains. In some ethnographically known instances, however, heads were simply discarded in the bush after being taken on raids, it being the act of taking the head that was of paramount importance – it is unlikely that evidence of such practices would be forthcoming archaeologically. But in many other cases, heads, whether of ancestors (however defined) or enemies, were retained, sometimes only for a short period, and sometimes for many decades. Here again, the division between the two can be blurred, as among the Naga hill tribes of north-east India, who took the heads of enemies but converted them into their own ‘ancestors’ who were meant to sustain fertili-ty of both people and crops (Hoskins 1996b)."
"And while only a small proportion of individuals may be involved, the application of clay ‘masks’ and amber or slate discs on the eyes of the deceased seems to be a distinctive feature of the eastern Baltic. Given the millennia separating Zvejnieki and the Finnish Corded Ware sites, this tradition may be a longstanding one."
Anthropology is keen on complex rituals, it construed the death of Otzi in that way, wrongly. After the Restoration, Oliver Cromwell's tomb was opened and his head publicly impaled on a spike. It was a ritual--of degradation and humiliation against a despised enemy.
@Sean, the whole paper addresses such matters and takes care to point out the complexities of interpretation. The severed head thing was found in Natufian Syro-Palestine and Iberomaurusian North Africa, but also in Magdalenian Europe: this is not surprising considering the universal cultural symbolism surrounding the human head, but there are not known Aurignacian or Gravettian examples. It at least helps to put Motala in a context.
Sean, perhaps more apropos is the example from King Philip's War, the conflict between the New England Indians and the colonists:
http://www.historynet.com/king-philips-war-indian-chieftains-war-against-the-new-england-colonies.htm
"The great King Philip–the most feared Indian in New England–was dead. The shot had been fired by John Alderman, one of Church’s trusted Indian friends. Like Crazy Horse 200 years later, King Philip was slain by a fellow Indian.
Church inspected the body of the fallen sachem and in disgust called him a doleful, great, naked, dirty beast. The captain’s men let out a loud cheer. Then Church ordered the body to be hacked to pieces, butchered in the manner of the standard English punishment for treason. As a reward, Alderman received Philip’s head and one hand. The rest of the sachem’s body was quartered and hoisted on four trees. Later Alderman sold the severed head to the Plymouth authorities for 30 shillings, the going rate for Indian heads during the war, and it was placed on a stake in Plymouth town, where the gruesome relic remained for the next 25 years."
https://gizmodo.com/human-skulls-mounted-on-stakes-found-at-8-000-year-old-1822936885
"As for the handling of the bodies after death and the mounting of heads on wooden stakes, that’s definitely weird. Mesolithic hunter-gatherers are not known to remove body parts like this; their grave sites show a respect for bodily integrity after death. That said, groups that appeared much later in history did decapitate their enemies, sometimes using the skulls of the vanquished as a trophy or warning. Historical examples include European colonists mounting the skulls of murdered indigenous peoples, or indigenous peoples using skulls in both burial rituals and as trophy displays."
White settlers picked up scalping from the Algonquians, but did the Algonquians take whole heads? I found a great book that says the Inuits collected whole heads but the Algonquians didn't, they took scalps.
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