Wyld Stallyns, Part Deux

A while ago, I wondered if modern stallions are a male morph adapted to domestication, one in which the strategy is mediated via the Y chromosome.

Looks as if I was right*. Check out “Decline of genetic diversity in ancient domestic stallions in Europe”.

Selection favored one particular kind of Y-chromosome. This had to be based on phenotype, not genealogy. Most likely it was favored under the new environment of domestication. Somehow, these stallions performed better, or were easier to get along with (my bet).

We already knew that Y-chromosomes could do things: Haplogroup I increases the risk of heart disease by about 50%, while the particular variant of Y chromosome influences aggression in mice.

Which means you have to re-examine the starburst phylogeny of R1b and R1a: it’s probably biology, rather than history, that drove those expansions. Some kind of selective advantage. Possibly one reason that those particular Y chromosomes far outraced steppe autosomal contributions. Most likely, R1a and R1b induce specific morphs – their carriers are somehow different. Maybe they’re born to be mild, or born to be princes of the universe. Maybe an R1b guy just finds it easier to cooperate with other R1b guys… Or maybe they’re resistant to typhoid.

* correct predictions mean nothing in biology. Ask any biologist.

Advertisements
This entry was posted in Uncategorized. Bookmark the permalink.

34 Responses to Wyld Stallyns, Part Deux

  1. Couldn’t Y chromosome expansion be explained due to patrilinear aristocracy?

  2. Lee Wang says:

    Congratulations on a (truly!) remarkable prediction.

    Some time ago on this blog during the revelations about the Indo-Europeans, a commenter brought up ‘Early Riders’ by Robert Drews. This commenter brought up a lot of other stuff, mostly inane and rightly got burned for it but I nevertheless found the argument interesting. Drews also wrote the excellent ‘ the End of the Bronze age’ so I thought I might give it a read.

    The argument goes as follows: traditionally, it is supposed that somewhere ~4000 BC, somebody domesticated the horse in the steppe. Nowadays, we would probably suspect the Proto-Indoeuropeans/Yamnaya. However, a couple facts don’t quite sit right; some horseriding was attested 4000-2000 BC but it looks very rare. The mid and late bronze age are instead characterized by kingdoms ruled by chariot-elites, some Indo-European derived (Mitanni…), some indigenous. Drews makes the argument that the chariot archer (they were all chariot archers) became obsolete ~1200 BC, which inaugurated the End of the Bronze age.
    From a military point of view, chariots are inferior to horses, so it seems that cavalry was unknown at this time.

    Furthermore, it seems we see widespread agriculture across the steppes in this period. Then in the 8th-6th century it suddenly disappears and is replaced by some form of pastoralism; attested horseriding becomes common, and various empires rise and fall due to the power of cavalry (Persians, Medes probably).

    Drews tries to argue that early people (4000-2000BC) knew the horse but surprisingly did not engage in serious horseriding. People might occasionally ride horses, but more as an extreme sport; apparently horseriding was seen as extremely dangerous in the Middle East at this time.
    For instance, he interprets early Yamnaya culture primarily as horse breeders for food and pulling wagons.

    It’s a funny and perhaps questionable argument for sure. Greg has made the very reasonable argument earlier that PIE-peoples might not have fought on horseback, but they probably used them for raiding etc. Nevertheless, it seems very peculiar that widespread horseriding and combat from horseback took so long. It seems such an obvious and extremely useful thing to do.

    From the paper linked in the OP:
    ” Moreover, among European horses, the haplotype representing modern Przewalski horses (Y-HT-2) was very abundant during the two older periods and even constitutes the most frequent one before 2200 BCE (oldest time bin). Haplotype Y-HT-1, on the other hand, which dominates in present-day stallions, was only detected later than 2200 BCE. Although its estimated age roughly correlates with the onset of domestication (3500 BCE; Fig. 4), this haplotype only started to become more frequent during later periods. All analyses indicate low Y-HT-1 frequency before 2200 BCE (fig. S1). However, the first time bin (>2200 BCE) only includes samples from Europe, with the easternmost samples falling on the longitude of the Black Sea (Fig. 2). Accordingly, Y-HT-1 could have been present with higher frequencies at that time in populations from further East. In the Iron Age (time bin 3, 900 BCE–400 CE), Y-HT-1 already represented the most frequent haplotype.”

    It seems to match the timeframe quite nicely. Drew doesn’t mention any possible biological causes in his book. Perhaps it can be argued that before tame male morphs were widespread, it was very difficult to make pastoralism/widespread horseriding work. On the other hand, what about mares?

    Second unrelated question: you have argued earlier for higher mutation rates in sub-Saharan Africans to explain higher deleterious mutation load in these populations. Possible reasons could be higher paternal age (Yoruba..? 5 year higher paternal age long term could give 20% elevated mutation rate) or some other cause – I like mitochrondial uncoupling here (especially as it jives with known differences in sperm motility). However, a more naive explanation would ascribe higher mutational load to genetic incompatibilities due to archaic introgression in Africans. I suspect that there are ways to tell these causes apart and you must already have thought about it: what is the solution?

    • gcochran9 says:

      I think the higher mutational load in Africa doesn’t really exist, barring malaria defenses. Thing is, even a slight increase in the extent of truncation selection is enough to remove quite a bit of load: it may well cancel out the mild increase in mutation rate from polygamy/older fathers.

    • Anonymous says:

      Horses were probably yoked quite early on by analogy to donkeys (donkeys and onagers were both used as draft animals in the Caucasus and Mesopotamia, and the Proto-Indo-Europeans had intimate connections to Caucasian groups for a good chunk of their early history – the Russians have done some good work on this). I privately suspect they were originally ridden in an attempt to make herding them easier – with raiding being the natural evolution of that as it allows you to get rustled cattle back home in an orderly fashion.

      Combat from horseback only seems obvious now because people spent a lot of time breeding horses that could be trained to ride straight into a dangerous situation and carry heavy enough loads. Early horses were quite small by modern standards, and I can’t imagine they’d have been overjoyed to have people climbing on top of them. Herodotus mentions that Medeans were breeding exceptionally large horses that could carry fully armoured men, but they were considered exceptional even in the 5th century BC.

      Also, for the first 4000 or so years of domestic horses, there were no saddles, stirrups, or spurs. The only thing the rider had to control the horse were reins and the bit, which made fighting from horseback a dangerious prospect at best – spears or clubs were your best bet, shooting would’ve been impossible. The Neo-Assyrians (who probably learned the technique from the Scythians or Parthians or some other Indo-Iranian group, who would’ve been living in a horseback nomadic culture for a long time by then) would have riders go out in pairs, with one shooting while the other took is reins to control the horse’s movement. Eventually they developed saddle cloths; probably another Scythian/Iranian invention. Virtually all early cavalry warfare techniques are Indo-Iranian in origin, because the Indo-Iranians were the ones who stayed with their horses on the steppe and came to rely on them more than any other group; everyone else was too much of a fucking casual.

      So chariots were a much more sensible proposition for actual fighting from horseback – one man controls the movement, one or more others can shoot. Even then, Chariots didn’t even show up until around 2000BC (another Indo-Iranian innovation), at which point people on the steppes had been living with horses for well over 1000 years. iIt spread very rapidly as soon as it was invented, but took a long time to be invented. Presumably it took people quite a long time to breed horses complacent enough/controllable enough to make this work, to say nothing of the training methodologies that would have to go with it. Interestingly, the 2000 BC date matches up just after the ‘modern’ haplotype starts to become more abundant – perhaps this is the point at which horses’ behaviour became predictable/controllable enough to make them useful for these purposes?

      • Lee Wang says:

        I agree. These things are also mentioned by Drews in his book. Another important point is that it is apparently very hard to get a horse to charge an infantry line. Early horses might have been even more unwilling to do so. He also mentions horses being ridden in the Middle East without bit but with a nose-ring (must be painful!).
        Indeed, the timeline is very striking; the Y-chromosome only becoming dominant in the Iron Age, exactly when widespread horse-riding, nodamism&pastoralism, cavalry appeared. Another point: apparently (chariot) horses were imported from the Iranian plateau& Caucasus and kings regularly complained about lack of supply; seemingly there were no local sources of horses, suggesting again that good breeding was paramount.

        • Anonymous says:

          This is borne out by modern day experiences. Horses from different lines within the same breed can be completely different in temperament. One line will consistently turn out good quality horses that are a joy to work with. The next will turn out jumpy, unbiddable uselessness, time and again.

          I suspect training was also as big a factor as distribution – one of the Mitanni horse training manuals is written in Hurrian with a lot of Indo-Ayran influence. Training horses would have had a near religious significance and would be unlikely to be shared widely. My best guess would be that the Hurrians and Urartians/ other Alarodian caucasians acted as the initial traders of high quality horses between the Indo-Iranians and the near east before picking up the techniques themselves (which would explain why the Sumerians referred to horses as ‘mountain donkeys.’)

        • Smithie says:

          Interesting to consider what traits may have been useful for warhorses. Seems like you would have to breed for aggression. Probably similar to some types of dogs, but try jumping on the back of a pitbull.

          From what I understand, horses would sometimes collide with each other on the battlefield. I don’t know if it involved blind spots or blinders, but, if not, it is hard to conceive that such a behavior could be induced by training alone,

          I remember seeing a Western where one character claimed it was safe to jump into the path of a horse, as a horse would try to avoid a person. He or a stuntman actually did it, but it was probably a trained horse.

      • myb6 says:

        I think we underestimate dragoon tactics.

      • Weren’t chariots using bows to flood enemy infantry with arrows and then retreat?
        Wasn’t it spoked wheel invention that made it possible?

  3. Douglas Knight says:

    Doesn’t the star-like phylogeny mean that the variant had a dramatic advantage in a narrow window of time, and doesn’t that suggest historical forces, rather than biological ones? Whereas the domesticable horse had a constant advantage over millennia.

    I suppose R1 could produce an inclination to or skill at a risky strategy of conquest. The risk paid off in a couple of historically contingent ways, R1a and R1b.

  4. M says:

    Could the later development of horse-riding be because:
    a) the horses were often too small to ride quickly (enough), but could still be used (in pairs etc) to pull chariots?
    b) the skills for horse archery are more difficult to create/learn than the skills for chariot archery (this might be tested empirically)
    c) if armor was a factor, then armoring someone in a chariot is a lot like armoring a foot soldier. Armoring a cavalryman has different requirements and these would have to be worked out.

    Not stating these as fact, but as questions.

    • Lee Wang says:

      a) Yes, this seems reasonable. Also, without this male morph tameness gene (and possibly related genes) they might be much harder to control. A chariot is safer and the horses are easier to control.

      b) Yes, very likely. A chariot is a stable platform in a way that a horse isn’t. I’ve heard it said that some Scythian bows (or was it Huns… I don’t quite remember) were asymmetric, the bottom being cut off to facilitate horse-riding.

      The rise of this horse archer is also strongly related to the introduction of the composite bow (Wikipedia mentions 2100-1700 BC in the Asiatic steppes, strikingly in a chariot burial!). In fact, the great bow of Odysseus is specifically mentioned to contain horn (i.e. be a composite bow). Composite bows are much better than self-bows but far harder to make and susceptible to humidity. I’ve heard conflicting evidence on how difficult it is to make a composite bow. Another very large cost is the archers training; archery is primarily strength based.

      c) In fact, chariot archers wore very heavy specialized armor; something like a very long bronze skirt that went down to the ankles (attested from Minoan Greece), very difficult to walk in and most likely too heavy for & impractical to ride with. Horses might also be armored.
      Other advantages of a chariot include the ability to carry large arrow supplies. OTOH the biggest disadvantage of a chariot archer is their cost: composite bow + 2 horses+ chariot+ lifelong training for archer + driver + attendant crew etc. They are also somewhat less maneuverable and slower than cavalry. Another big disadvantage of chariots is their susceptibility to javelineers. Possibly pioneered by the Hittites javelineers would try to hit the horses or the wheels, crashing the chariot. Drews thinks this was one of the reasons behind the decline of chariot archers – and by extension the hierarchical Late Bronze age societies on which they were based.

      • DRA says:

        …Scythian bows (or was it Huns… I don’t quite remember) were asymmetric, the bottom being cut off to facilitate horse-riding.

        I read an article that speculated on who developed the asymmetric bow, with the Scythians the authors best guess. Then I visited a museum in Arizona, near the Dragoons, and Cochise evidently had an asymmetric bow, which was prominently displayed. Don’t know that he ever met a Scythian.

  5. Arterial vigor says:

    What advantage could an allele or a number of alleles increasing cardiovascular disease confer? Back in the day, when the average life expectancy was 30 years, I guess it didn’t matter so much as it does nowadays, since you would probably die from whatever before your arteries clogged.
    Is it aggression? Increased testosterone levels? Higher sperm count? Or just a glitch?

    • GAGCAT says:

      Speculating here – there might be a tradeoff between disease in later life and better recovery from a bleeding wound from hunting or warfare.

  6. Anonymous says:

    The change in Y-chromosomes wasn’t gradual but effectively instant so the Indo-European invasion might be a bad example? The explosive growth of I1, heart disease or no heart disease might be a better example as it’s not linked to an invading population in Northern Europe.
    In theory, populations which are large have a deeper pool of competing Y-DNA/mtDNA while small populations with regular bottlenecks might have issues.

  7. A mutation on the Y chromosome that skews the sex ratio toward males (e.g. killing X bearing sperm) can spread very quickly, but will also set up selection for modifiers in the rest of the genome that have the opposite effect, so the effect will probably be transient. I’m not sure how plausible this is for either horses or Indo-Europeans. Of course, “selfish” DNA mutations like this are more common in large populations, just like garden-variety beneficial mutations.

      • RCB says:

        Fisher’s argument originally treated autosomal genetic variants. The Y chromosome case is one exception to the generalization that selection favors 50-50 sex ratios. Basically, for Y chromosomes, females are a waste of energy. And yes, once the ratio is off of 50-50, there will be selection for variants in the rest of the autosomal DNA that bring it back to 50-50. Intragenomic conflict. No general reason why one should be winning at any given time – except, I guess, that the Y chromosome is very small compared to the rest of the genome.

        Similarly, there are lots of known mitochondrial DNA mutations in plants that lead to suppression of male function. Same principle working in the other direction. To a mitochondrion, males are a waste of energy.

  8. Smithie says:

    I have one of those old names, and I remember feeling oddly disappointed when the current thinking seemed to move to the theory that the gene for hairy ears isn’t on the Y-chromosome.

  9. sprfls says:

    And perhaps G2a bestows those magic eastern Mediterranean mercantile skillz. :’-)

  10. Smithie says:

    Will it hold up for camelids?

  11. zig says:

    I am R1b and have been told I have “super” sperm with excellent motility.

    Just one data point

    • Denis Anderthal says:

      I’m R1b also and have been told I have “super’ sperm as well, with excellent shape and motility. I also think I’m relatively mild. Maybe our line in northern Asia went through some kind of bottleneck there, with few surviving, and then R1b-M269 really expanded with the bell beakers in Germany.

  12. Reziac says:

    How do you know all the ancient male horses examined were stallions? The narrow Y diversity may simply indicate when humans discovered gelding them to improve tractability. If they’re gelded after sexual maturity, that negates the skeletal differences. (At present probably 98% of male horses are gelded.)

  13. Magus says:

    Random thoughts: was there also some effect from R1A? just eyeballing a map it seems R1b societies have higher social trust on avg than R1A. Historical quirk from Middle Ages or is causation reversed? And if R1b só great why did R1A Chase us West? Do we have different advantages? They’re tougher but less social (Ruskies), we are more social but less tough, or is that just cultural evolution from last few hundred years ie R1B was equally ferocious 500 years ago if not less?

    And is it curious how R1A and R1B popped up roughly same time? What conditions twice led to such massive advantages? Inherited from ANE?

  14. crew says:

    In line with recent findings indicating that the Przewalski and domestic horse lineages remained connected by gene flow after they diverged about 45,000 years ago, we present evidence for Y chromosomal introgression of Przewalski horses into the gene pool of European domestic horses at least until medieval times.

    Wait. Are they saying that domestication commenced sometime around 45,000 years ago, or that domestication occurred using a lineage that diverged around 45,000 years ago?

  15. R1 Selection says:

    R1b qua R1b as an advantaged variant, is kind of a weird idea, because we see R1b-V88 around at fairly low but persistent frequencies among early EEF, in at least Spain and possibly the Balkans, and probably with enough effort in ancient Anatolia, and among various WHG in Europe as well.

    Indeed this is V-88 is the lineage of Chadian R1b, which also undergoes a late starburst expansion, after getting there from either Iberia or the Near East.

    But no major starburst expansion of R1b among the Atlantic Neolithic, or European Neolithic at all; instead we see the dominance of I2, possibly from WHGs.

    (Cites: R1b V-88 has a nice steady state expansion in general since the Neolithic, at about 10kya – https://link.springer.com/article/10.1007%2Fs00439-017-1773-z. No special recent starburst.

    But R1b V-88 variants frequent in North Africa do have a star-like expansion, much more recently – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5809971/).

    So if there is something selectively special about R1, it probably has to happen later in history and independently in three lineages; the lineage ancestral to R1a variants that later become frequent in Eastern Europe and India, the lineage ancestral to R1b lineages that become important in Western European, and probably this African subtree of R1b-V88. And it has to happen at points which are exactly aligned with the general demographic expansion of early Eurasian steppe pastoralists and of pastoralists into the Sahara.

    And at the same time, it has to not happen in all the basally diverse R1b-V88 that’s about in the Near East and expanding on a steady, slow, state since the Neolithic…

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s