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The Sex Ratio Is in the X
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k8488 In The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World the archaeologist David Anthony outlines the thesis that migrations from the west Eurasian steppe during the Bronze Age reshaped the culture of Northern Europe. When Anthony published the book, which you should really read if you are interested in this topic, it was a somewhat heterodox position. Though his intellectual pedigree is of long standing, arguably going back centuries, and extending down the present with J. P. Mallory’s In Search of the Indo-Europeans, in the past few decades diffusion of different sort has been paramount. In particular, the thesis that Indo-Europeans arrived with the first agriculturalists was of late ascendant, with some support being received from phylogenetic modeling of language evolution.

Anthony’s thesis in a way was a halfway house between early modern migrationism from the Eurasian steppe the newer theories. He proposes that the influence from the steppe via the Kurgan people was due to elite dominance and cultural emulation. An analogy here might be that of Hungary, where a Ugric speaking elite eventually imparted to the people a language, but very few distinct genes.

Eventually Anthony collaborated with some geneticists, and provided samples for DNA analysis. The results ended up resulting in a resurrection of migrationism, Massive migration from the steppe was a source for Indo-European languages in Europe. From what I have heard Anthony’s reaction was one of some shock as the magnitude of the genetic change.

5156rR+E2lL._SX326_BO1,204,203,200_ That’s the high level view. But what about the details? Over the past few years I’ve highlighted work that indicates that many Y chromosomal lineages are star-shaped. That is, they underwent recent demographic expansion. Recent as in on the order of ~5,000 years ago in the past. But the Y chromosome is just one locus. I’ve always been curious about results from the X because the X also gives you good sex specific dynamics; 2/3 of the time it is spent in females, and 1/3 of the time in males.

Amy Goldberg has done so, Familial migration of the Neolithic contrasts massive male migration during Bronze Age in Europe inferred from ancient X chromosomes:

Dramatic events in human prehistory, such as the spread of agriculture to Europe from Anatolia and the Late Neolithic/Bronze Age (LNBA) migration from the Pontic-Caspian steppe, can be investigated using patterns of genetic variation among the people that lived in those times. In particular, studies of differing female and male demographic histories on the basis of ancient genomes can provide information about complexities of social structures and cultural interactions in prehistoric populations. We use a mechanistic admixture model to compare the sex-specifically-inherited X chromosome to the autosomes in 20 early Neolithic and 16 LNBA human remains. Contrary to previous hypotheses suggested by the patrilocality of many agricultural populations, we find no evidence of sex-biased admixture during the migration that spread farming across Europe during the early Neolithic. For later migrations from the Pontic steppe during the LNBA, however, we estimate a dramatic male bias, with ~5-14 migrating males for every migrating female. We find evidence of ongoing, primarily male, migration from the steppe to central Europe over a period of multiple generations, with a level of sex bias that excludes a pulse migration during a single generation. The contrasting patterns of sex-specific migration during these two migrations suggest a view of differing cultural histories in which the Neolithic transition was driven by mass migration of both males and females in roughly equal numbers, perhaps whole families, whereas the later Bronze Age migration and cultural shift were instead driven by male migration, potentially connected to new technology and conquest.

Screenshot 2016-09-30 22.33.39 The figure to the left shows the inferences made in regards to the quantitative contribution of farmer males and females, and steppe males and females, to Bronze Age European populations. In short, it looks like the population of Northern Europe derives from a fusion of males from the steppe, and native females, who themselves arose out of a group of peoples which synthesized the ancestry of European hunter-gatherers and West Asian farmers.

But one of the more interesting things about this preprint is that the admixture can’t be modeled by a single pulse event. It seems that there were repeated migrations out of the steppe over multiple generations. But, these men did not bring women, at least in large numbers. The preprint lays out the common sense reason: these were mobile groups, probably bands of men with weapons. If your game is predation on other humans, having a baggage train of women and children is not optimal.

There is a historical analog to what might have happened. Argentina is a nation where mitochondrial lineages show a lot of Amerindian heritage. But the whole genome far less. This is because of male biased migration from Europe. One generation of this would result in a mixed population, but many generations would slowly replace the whole genome.

We will never know in concrete terms what social-political organizations the Indo-Europeans set up once they conquered the plains of Northern Europe, because we don’t have writing. But it seems unlikely that we’re talking about only band or clan level scales of organization. Rather, it was likely that a ‘Indo-European commonwealth’ of some sort existed initially, predicated on domination and extraction of value from the natives. In such a fashion one can imagine Europe being a draw for enterprising males from the steppe. This could also explain likely ‘back migration’ over time, leading to ‘European’ ancestry among later steppe cultures.

 
• Category: Science • Tags: Ancient DNA, Genomics 
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  1. This suggests that the impulse to empire and colonialism is rooted far back in IE history.

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    • Replies: @Tobus
    I think this "impulse" is really just a function of technological superiority. There are examples of empire and colonisation in Native Americans, East Asians, South Asians, Middle Easterners and Africans, it's not a unique trait of IE speakers.
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  2. @gruff
    This suggests that the impulse to empire and colonialism is rooted far back in IE history.

    I think this “impulse” is really just a function of technological superiority. There are examples of empire and colonisation in Native Americans, East Asians, South Asians, Middle Easterners and Africans, it’s not a unique trait of IE speakers.

    Read More
    • Replies: @gruff
    That just pushes the question back to "where does technological superiority come from". And no Jared Diamond does not have the Endtheorie.
  3. Lipka Tatars of Belarus for their part show a balance of eastern Turkic-like mtDNA and genome-wide contribution (they’re actually more eastern than Volga Tatars). One could speculate there was less sex bias in the Turkic expansions.

    http://www.nature.com/articles/srep30197

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  4. Huh. It’s weird to think that an explanation I read for warrior aristocracy possibly back when I was in middle school and just looking at books in the library (that they were violent wanderers and raiders who conquered farming areas) turned out to be right after all.

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  5. I’m not going to say that it wasn’t a male biased migration, but the same genetic result would occur if the migration was half male, but these men took many additional local wives in the new land.

    The genetics would be amplified if the 2nd generation sons also did the same, and took many local wives. Their (steppe) Y chromosome would be passed on to all sons, along with their purely local (non-steppe) X chromosome to all of their daughters.

    I think this requires polygyny and a male dominated society to make sense.

    Read More
    • Replies: @Dmitry Pruss
    My thought too. I checked the preprint and they don't use polygamy hypothesis anywhere.

    Another case in point. Steppe Pontic populations were significantly taller and more robustly built than late Neolithic Europeans with their smaller body sizes and short stature (and the ancestors of the invading early agriculturalists were generally shorter in stature than the hunter-gatherers). Isn't there a strong correlation between polygamy-like mating patterns and stronger sexual dimorphism of body sizes / increasing male-to-female body size ratio? Across species?

    Perhaps the polygynous mating patterns of the Steppe migrants are biological rather than purely social in origin, enabled by unusually small relative body sizes of the available females?

    (And conversely, the relatively small male body size of the early farmers would have agreed with smaller harem sizes even if it was culturally favored to take multiple wives)

  6. Has anyone checked for the a similar genetic pattern in Hutu populations? Tutsi intermarried with the horticultural populations they dominated. It might be useful to look for similar patterns in the case of other outward spreading predatory pastoral economies. In fact. the entire prehistory of the Bantu-language agro=pastoral expansion southward through central Africa might be another example of this kind of phenomenon.

    Read More
    • Replies: @Razib Khan
    ideological reasons hard to get some samples from those two populations.
    , @Erik Sieven
    so do I understand this comment right: Bantus might have been the equivalent of "native" Europeans in Ruanda and the equivalent of IE´s in the rest of central/south-west Africa?
  7. @Helga Vierich
    Has anyone checked for the a similar genetic pattern in Hutu populations? Tutsi intermarried with the horticultural populations they dominated. It might be useful to look for similar patterns in the case of other outward spreading predatory pastoral economies. In fact. the entire prehistory of the Bantu-language agro=pastoral expansion southward through central Africa might be another example of this kind of phenomenon.

    ideological reasons hard to get some samples from those two populations.

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    • Replies: @Helga Vierich
    I don’t see why- there have been many researchers through that region even since the genocides took place. Forensic work alone would provide a pile of interesting DNA results.
  8. Helga Vierich [AKA "Helga Vierch"] says:     Show CommentNext New Comment
    @Razib Khan
    ideological reasons hard to get some samples from those two populations.

    I don’t see why- there have been many researchers through that region even since the genocides took place. Forensic work alone would provide a pile of interesting DNA results.

    Read More
    • Replies: @Razib Khan
    my understanding is that the current rwandan gov. wants to deemphasize hutu/tutsi differences. years ago i looked at the 23andMe genotype of someone who was 1/2 tutsi. they were shifted strongly toward cushitic populations in proportion to their admixture.

    yes, there are samples.
  9. @Helga Vierich
    I don’t see why- there have been many researchers through that region even since the genocides took place. Forensic work alone would provide a pile of interesting DNA results.

    my understanding is that the current rwandan gov. wants to deemphasize hutu/tutsi differences. years ago i looked at the 23andMe genotype of someone who was 1/2 tutsi. they were shifted strongly toward cushitic populations in proportion to their admixture.

    yes, there are samples.

    Read More
  10. @Helga Vierich
    Has anyone checked for the a similar genetic pattern in Hutu populations? Tutsi intermarried with the horticultural populations they dominated. It might be useful to look for similar patterns in the case of other outward spreading predatory pastoral economies. In fact. the entire prehistory of the Bantu-language agro=pastoral expansion southward through central Africa might be another example of this kind of phenomenon.

    so do I understand this comment right: Bantus might have been the equivalent of “native” Europeans in Ruanda and the equivalent of IE´s in the rest of central/south-west Africa?

    Read More
  11. @Rick
    I'm not going to say that it wasn't a male biased migration, but the same genetic result would occur if the migration was half male, but these men took many additional local wives in the new land.

    The genetics would be amplified if the 2nd generation sons also did the same, and took many local wives. Their (steppe) Y chromosome would be passed on to all sons, along with their purely local (non-steppe) X chromosome to all of their daughters.

    I think this requires polygyny and a male dominated society to make sense.

    My thought too. I checked the preprint and they don’t use polygamy hypothesis anywhere.

    Another case in point. Steppe Pontic populations were significantly taller and more robustly built than late Neolithic Europeans with their smaller body sizes and short stature (and the ancestors of the invading early agriculturalists were generally shorter in stature than the hunter-gatherers). Isn’t there a strong correlation between polygamy-like mating patterns and stronger sexual dimorphism of body sizes / increasing male-to-female body size ratio? Across species?

    Perhaps the polygynous mating patterns of the Steppe migrants are biological rather than purely social in origin, enabled by unusually small relative body sizes of the available females?

    (And conversely, the relatively small male body size of the early farmers would have agreed with smaller harem sizes even if it was culturally favored to take multiple wives)

    Read More
  12. This phenomenon here is quite discernible because of the deep divergence between the two populations involved and we have the adna, but it seems fairly thinkable that similar phenomena (male biased expansions) to some degree could’ve happened between two populations who were less readily discernable, especially without adna. Like different Native American populations or within Africans or within East Asia.

    Read More
  13. @Tobus
    I think this "impulse" is really just a function of technological superiority. There are examples of empire and colonisation in Native Americans, East Asians, South Asians, Middle Easterners and Africans, it's not a unique trait of IE speakers.

    That just pushes the question back to “where does technological superiority come from”. And no Jared Diamond does not have the Endtheorie.

    Read More
    • Replies: @Sean
    Don't write off Diamond. Wars are won by concentrating force against weakness, in other words you need local superiority in numbers to win. Diamond's book has"germs" in the title. Neolithic Farmers were no strangers to organised warfare and raiding, and surly far more numerous than those who conquered them. One would think that as the Yamnaya pushed into farmer territory they would face ever greater concentrations of farmers. Yet the farmers must have been always outnumbered at the point of contact to lose so constantly. Maybe Diamond has a point and it was germs ( plague brought by the Yamnaya) that thinned out the farmers and sealed their fate.
  14. What did diamond say when asked “why do you have so much cargo”?

    He wasn’t ready with an answer but he KNEW it couldn’t be genetic!

    Turns out that was the null hypothesis.

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  15. @gruff
    That just pushes the question back to "where does technological superiority come from". And no Jared Diamond does not have the Endtheorie.

    Don’t write off Diamond. Wars are won by concentrating force against weakness, in other words you need local superiority in numbers to win. Diamond’s book has”germs” in the title. Neolithic Farmers were no strangers to organised warfare and raiding, and surly far more numerous than those who conquered them. One would think that as the Yamnaya pushed into farmer territory they would face ever greater concentrations of farmers. Yet the farmers must have been always outnumbered at the point of contact to lose so constantly. Maybe Diamond has a point and it was germs ( plague brought by the Yamnaya) that thinned out the farmers and sealed their fate.

    Read More
  16. But one of the more interesting things about this preprint is that the admixture can’t be modeled by a single pulse event. It seems that there were repeated migrations out of the steppe over multiple generations. But, these men did not bring women, at least in large numbers. The preprint lays out the common sense reason: these were mobile groups, probably bands of men with weapons. If your game is predation on other humans, having a baggage train of women and children is not optimal.

    Obviously the women were not taken on actual raids, but that is a very different thing from saying the migrations (lasting a generation) were only 7% female. This wasn’t a case of a desperately perilous sea journey such as was required to reach the new world. The Yamnaya migrated while they were continuing their lifestyle as herders and warriors, and women have much work to do in such societies. It’s more likely there were lots of women on the migrations but they didn’t reproduce as much as the men.

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  17. @ Dmitry – height stuff seems like this at the moment – https://pbs.twimg.com/media/CSQAwPGXAAAPo69.jpg. Neolithic farmers of Northern Europe more similar to steppe groups than Neolithic farmers from Iberia. Bronze Age groups not intermediate to the two.

    Using the heights of present day people to calibrate Sardinians 5’7″ and CEU (British) 5’10″, so that would imply Iberian Neolithic 5’5″, North European Neolithic 5’9″, North European Bronze Age 5’9″, Steppe 5’11″ or 6″. In itself you would not expect that difference to matter so much between North European Neolithic and steppe groups, but could have a role, also if reinforced by higher nutrition among Yamnaya pastoralist groups. And anyway, maybe the Yamnaya conquered South European Neolithic on the way in to Europe, and not the North European ones.

    Here – http://www.nature.com/nature/journal/v528/n7583/images/nature16152-f4.jpg -the Euro HG group (a gaggle of different HG from Scandinavia and the rest of Europe) would probably be placed at around 5’9″ as well – or at any rate at a similar height to the North European Neolithic group.

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  18. Mr Khan,

    it would be interesting to speculate on how migrations from the British Isles and France to Eastern Canada and United States ”reshaped” the life of Native Americans (mainly hunter-gatherers).

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  19. […] fall I bloggeda preprint which eventually came out as a paper in PNAS, Ancient X chromosomes reveal contrasting […]

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