Update: Women and red hair

The online magazine Evopsy has posted a summary, in French, of the paper on red hair that I wrote with Karel Kleisner and Jaroslav Flegr. It can be found here.

The online magazine Cultura VRN has posted a summary, in Russian, here.

Please let me know about any other magazines that might be interested in this topic.

References

Frost, P. (2018). Pыжая женщина – уникальна, Cultura VRN, January 15

http://culturavrn.ru/world/23304 

Frost, P. (2018). La rousse est particulière, Evopsy, January 7

http://www.evopsy.com/abstracts/rousse-frost.html 

Frost P, Kleisner K, Flegr J (2017) Health status by gender, hair color, and eye color: Red-haired women are the most divergent. PLoS ONE 12(12): e0190238. 

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190238  

The people before the First Nations

Aeta woman (Philippines) – Wikipedia (Ken Llio)

Modern humans pushed out of Africa along two routes: a northern one through the Levant and into Europe and a southern one along the Indian Ocean coast and eventually into New Guinea and Australia. The southern route is said to have had two waves: an earlier one between 62,000 and 75,000 years ago that was ancestral to present-day Australian Aborigines and a later one between 25,000 and 38,000 years ago that was ancestral to present-day Negrito groups in Southeast Asia: the Andaman Islanders, the Semang of the Malayan Peninsula, and the Aeta of the Philippines, although these groups would have intermixed with the population already present from the first wave (Rasmussen et al. 2011; Reyes-Centeno et al. 2014).

Did this southern route end in Southeast Asia or did it swing north along the Pacific coast? We know that the Philippines was once inhabited by Negritos—the country still has over thirty such groups. In addition, there have been claims that a Negrito group used to live on Taiwan. In the early 20th century, the anthropologist Rolange Dixon argued that a Negrito population once occupied the whole of the South, Southeast, and East Asian littoral:

At this time the southern and eastern borderlands, from India around to Kamchatka, seem to have been occupied in the main by a dolichocephalic, dark-skinned, Negroid population which was a blend in varying proportions of the Proto-Australoid and Proto-Negroid types. There is some evidence which leads us to believe that this Negroid population extended farther westward than India, along the shores of the Persian Gulf and the southern coast of Arabia, so being continuous with the great area held by similar peoples in Africa. (Dixon 1923, p. 243)

In the late 20th century, interest declined in Negritos and their place in human prehistory, partly because anthropologists were increasingly taking an ahistorical approach hunter-gatherers and shunning anything that smacked of racial or evolutionary thinking. Though a student of Franz Boas, Dixon studied anthropology (1897-1906) at a time when Boas believed not only in the existence of human races but also in psychological differences between them, albeit in a statistical sense (Frost 2014, Frost 2015). Furthermore, genetic studies in the late 20th century seemed to show that different Negrito groups had little in common with each other. Clearly, Negritos are a very ancient population, and the time to the most recent ancestor for all of them is greater than it is for, say, present-day Europeans and present-day East Asians. They still look similar to each other only because they remained under similar climatic and cultural conditions.

Recent years have seen a renewal of interest in Negritos. Mitochondrial DNA studies have shown that they are indeed the remnants of a southern "Out of Africa" route, together with New Guineans and Australian Aborigines (Reyes-Centeno et al. 2014; Stoneking and Delfin 2010; Thangaraj et al. 2005). Of particular interest is the discovery of significant admixture from these peoples in Amerindians from Amazonia and the Central Brazilian Plateau (Skoglund et al. 2015). This admixture seems to be very old:

The genetic data allow us to say with confidence that Population Y ancestry arrived south of the ice sheets anciently: the fact that the geographically diverse Andamanese, Australian and New Guinean populations are all similarly related to this source suggests that the population is no longer extant, and the absence of long-range admixture linkage disequilibrium suggests that the population mixture did not occur in the last few thousand years.

As the authors note, this finding is consistent with ancient skeletal remains from the same region:

This discovery is striking in light of interpretations of the morphology of some early Native American skeletons, which some authors have suggested have affinities to Australasian groups. The largest number of skeletons that have been described as having this craniofacial morphology and that date to younger than ten thousand years have been found in Brazil6, the home of the Suruí, Karitiana and Xavante who in genetic data show the strongest affinity to Australasians.

How did this population reach the Amazonian basin? Perhaps the same way the Paleo-Amerindians did: across the Bering Strait and down through North America. If Negrito groups had reached south China and the Philippines, they could have continued up the East Asian shoreline and then down the west coast of North America. One problem with this model, raised by Greg Cochran and Steve Sailer, is that the "Australasian" admixture is absent from native North Americans. Keep in mind, however, that at least three waves of migration entered North America: the latest one corresponding to the Inuit-Aleut peoples, an earlier one corresponding to the Na-Dene peoples, and the earliest one corresponding to all other Amerindian groups. Only this earliest wave reached South America. There has consequently been much more population replacement among native North Americans than among native South Americans.

Population replacement is widely seen as something that has been done by European peoples (and, more recently, which is being done to them). In reality, the world was not a static place before Columbus. Human populations have been replacing each other for a very long time.

References

Cochran, G. (2018). Beringians, West Hunter, January 4

https://westhunt.wordpress.com/2018/01/04/beringians/

Dixon, R.B. (1923). The Racial History of Man, New York: Charles Scribner's Sons.

https://archive.org/stream/racialhistoryofm01dixo/racialhistoryofm01dixo_djvu.txt 

Frost, P. (2014). The Franz Boas you never knew, Evo and Proud, July 13 http://evoandproud.blogspot.ca/2014/07/the-franz-boas-you-never-knew.html 

Frost, P. (2015). More on the younger Franz Boas, Evo and Proud, April 18

http://evoandproud.blogspot.ca/2015/04/more-on-younger-franz-boas.html 

Rasmussen M, et al. (2011) An Aboriginal Australian genome reveals separate human dispersals into Asia, Science, 334(6052), 94-98.

http://europepmc.org/articles/pmc3991479

Reyes-Centeno, H., S. Ghirotto, F. Détroit, D. Grimaud-Hervé, G. Barbujani, and K. Harvati. (2014). Genomic and cranial phenotype data support multiple modern human dispersals from Africa and a southern route into Asia, PNAS, 111(20), 7248-7253.

https://s3.amazonaws.com/academia.edu.documents/40683950/Reyes-Centeno_et_al_2014.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1515619505&Signature=vu3uoN4c27lg0S3KhEsSWQw%2B4S4%3D&response-content-disposition=inline%3B%20filename%3DGenomic_and_cranial_phenotype_data_suppo.pdf 

Sailer, S. (2018). Were There People Already in the New World When the Indians Arrived? The Unz Review, January 6

http://www.unz.com/isteve/were-there-people-already-in-the-new-world-when-the-indians-arrived/

Skoglund, P., S. Mallick, M.C. Bortolini, N. Chennagiri, T. Hunemeier, M.L. Petzl-Erier, F.M. Salzano, N. Patterson, and D. Reich. (2015). Genetic evidence for two founding populations of the Americas, Nature, 525, 104-108

https://reich.hms.harvard.edu/sites/reich.hms.harvard.edu/files/inline-files/nature14895_Skoglund_2015.pdf

Stoneking, M. and F. Delfin (2010). The Human Genetic History of East Asia: Weaving a Complex Tapestry, Current Biology, 20(4), R188-R193 

http://www.sciencedirect.com/science/article/pii/S0960982209020673

Thangaraj, K., G. Chaubey, T. Kivisild, A.G. Reddy, V.K. Singh, et al. (2005). Reconstructing the origin of Andaman Islanders, Science, 308(5724), 996

https://www.researchgate.net/profile/Gyaneshwer_Chaubey/publication/7850233_Reconstructing_the_Origin_of_Andaman_Islanders/links/09e41508a88bf4dc2a000000.pdf

Red-haired women are special

The Damsel of the Sanct Grael – Dante Gabriel Rossetti (1828-1882)

It's known that red-haired women, but not red-haired men, are more sensitive to pain. Red hair is also associated with a higher risk of developing endometriosis, Parkinson's disease, and decreased platelet function.

A study in the latest issue of PLoS One has confirmed that red hair, especially in women, is linked to certain health issues. According to a survey of over seven thousand participants, red-haired women do worse than other women in ten health categories and better in only three, being especially prone to colorectal, cervical, uterine, and ovarian cancer. Red-haired men seem to be as healthy as other men, doing better in three categories and worse in three. Reproductive success, i.e., number of children, is the only category where redheads of both sexes do better than other participants.

This study has also confirmed that red hair is naturally more frequent in women than in men. To a lesser degree, the same is true for blond hair and green eyes. These bright colors seem to result from a selection pressure that mainly targeted women, i.e., sexual selection. In other words, among early Europeans there were too many women and not enough men; hence, competition between women for mates favored those who could better catch the attention of men, such as through a palette of bright hair and eye colors.

Because women are overrepresented among redheads, it may be that estrogen promotes synthesis of red pigments by hair follicles, particularly during fetal development. Thus, if a baby is born red-haired and female, estrogenization of its body tissues should be, on average, near the top end of the normal range. It will therefore be more at risk of developing certain health issues.

Another hypothesis can be put forward. If red hair was the last hair color to evolve, the underlying alleles may not have finished adapting to the rest of the genome, and vice versa. This reciprocal adaptation is all the more necessary because one of the five alleles for red hair seems to be of Neanderthal origin. The hypothesis of incomplete adaptation does not exclude the hypothesis of high estrogenization. In fact, there may be interaction between the two factors. Although it's likely that sexual selection did produce new hair and eye colors, we must still explain why, in this palette of colors, red hair seems to show the greatest difference between men and women both in population frequency and in associated health effects. 

Reference

Frost P, Kleisner K, Flegr J (2017) Health status by gender, hair color, and eye color: Red-haired women are the most divergent. PLoS ONE 12(12): e0190238. 

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190238

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La rousse est particulière

On sait que les rousses, mais pas les roux, sont plus sensibles que les autres à la douleur. La rousseur est également associée à un plus grand risque de développer l'endométriose, la maladie de Parkinson, ainsi que des troubles de l'agrégation plaquettaire.

Une étude publiée dans le dernier numéro de la revue PLoS ONE confirme que la rousseur, surtout chez la femme, est reliée à certains problèmes de santé. Selon une enquête menée auprès de plus de sept mille participants, les rousses se classent pire que les autres femmes dans dix catégories de santé et mieux dans seulement trois, étant surtout susceptibles de développer des cancers du gros intestin, du col utérin, de l'utérus ou des ovaires. Quant aux roux, leur état de santé ressemble à celui des autres hommes : mieux dans trois catégories et pire dans trois. Le succès reproducteur, soit le nombre d'enfants, est la seule catégorie où les têtes rouges des deux sexes font mieux que les autres participants.

Cette étude confirme également que la rousseur est naturellement plus fréquente chez la femme que chez l'homme. Dans une moindre mesure,  c'est le même constat avec la blondeur et les yeux verts. Ces couleurs vives semblent être le résultat d'une pression de sélection visant surtout la femme, soit la sélection sexuelle. Autrement dit, il y aurait eu trop de femmes et pas assez d'hommes chez les premiers Européens, avec pour résultat une concurrence entre les femmes favorisant celles qui attiraient mieux les regards des hommes, comme par exemple par une palette de couleurs vives décorant les cheveux et les yeux.

Les femmes étant surreprésentées parmi les têtes rouges, on peut émettre l'hypothèse que l'œstrogène favorise la synthèse de pigments rouges dans les follicules pileux, particulièrement au cours du développement fœtal. Alors, si un enfant nait à la fois roux et de sexe féminin, l'œstrogénisation de ses tissus organiques doit être, en moyenne, vers la limite supérieure de la normale. La rousse sera donc plus à risque de connaitre certains problèmes de santé.

Une autre hypothèse est possible. Si la rousseur a été la dernière couleur de cheveux à paraître, il se peut que les allèles sous-jacents n’aient pas encore fini de s'adapter au reste du génome et vice versa. Cette adaptation réciproque est d'autant plus nécessaire parce que l'un des cinq allèles pour la rousseur semble être d'origine néandertalienne. Notons que l'hypothèse d'adaptation incomplète n'exclut pas celle de forte œstrogénisation. En fait, il pourrait y avoir une interaction entre les deux facteurs. S'il est vraisemblable que la sélection sexuelle ait produit de nouvelles couleurs des cheveux et des yeux, il faudra toujours expliquer pourquoi, dans cette palette de couleurs, la rousseur semble montrer la plus grande différence entre les hommes et les femmes, autant en termes de fréquence dans la population que sur le plan de la santé.