Y-chromosome crash

A recent paper on  Y-chromosome phylogeny  found that a big fraction of Y-chromosomes  fall into a few star-cluster lineages that are a few thousand years old.  You’ve  already heard of some of these (R1a and R1b, for example).

I might be wrong, but I get that the impression that some people have gravely misunderstood what this means.  For example, something at Slate  writing about this work seems to think that back in those old times, only one man passed on his DNA for every 17 women.  Others apparently got the same impression.

Let’s think about it. If only 1 in 17 men reproduced, Y-chromosome diversity would be reduced, all right – but overall genetic diversity, autosomal diversity, would also decrease, which apparently has not actually happened, as Alan Rogers has pointed out.  More than that: is such a society, one in which 94% of men never reproduce, very plausible?  Would it be stable? Reminds of a case in which some drunken soldiers wandered into a hard-core Baptist church service, and after an inspired sermon on the torments of Hell,  objected: “There couldn’t be no sich place! People wouldn’t stand for it !”

Such a society would be like the famous car-wash scene in Cool Hand Luke – all the time.

Here is a more plausible scenario, one that fits the facts. Some conqueror has an inordinate number of kids (because he can).  His sons, and his sons’ sons,  rule for a long time – eventually most of the aristocracy are their male-line descendants.  That first generation had a huge reproductive advantage, but we’re only talking one guy:  if our hero had 100 wives,  that doesn’t make much difference in the overall fraction of men that reproduce.  As the generations pass, his patrilineage gets bigger but their average  reproductive advantage becomes smaller (they can’t ALL be kings). The conqueror’s autosomal contribution is cut in half each generation ( at least while this patrilineage doesn’t make up much of the total population) , unlike his Y chromosome: his genes never make up much of the overall autosomal ancestry, even when most of the men in the population have his Y-chromosome.   Autosomal genetic diversity is hardly reduced, effective Ne does not drop noticeably, while the Y chromosome is almost fixed – would be, except for continuing mutations.

Let’s suppose that this process (one  Y chromosome becomes dominant in this Genghis-Khanish way) takes place over a thousand years.  I think at the worst point, the fraction of guys having offspring is probably 80% as large as it was back in the egalitarian days of old.

Genetic inequality may have increased some. The rich may well have out-reproduced the poor, although with cities as population sinks, you can’t be sure. In Europe, this process surely involved conquest, likely with a lot of indigenous old-farmer men getting whacked.

But only 5 0r 10% of guys fathering kids in a given generation?  Never happened.


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60 Responses to Y-chromosome crash

  1. Good argument.

    Just to note that in pre-industrial times, the crucial factor (although not the only one) was not fertility/ births (which were probably high all round) but child mortality – i.e. whether or not these children who were born survived to sexual maturity.

    So in the above alternative scenario; among the Y-chromosome dynasty, the crucual factor would probably have been the handing-on, down the male line of descent, of the ability to raise sons to adulthood.

    (This inheritance would have to include material advantages, I think, implying patrilineal inheritance among a ruling class able to extract the lion’s share of resources from those they ruled).

    I agree it is implausible that asociety could for long restrict sex/ fertility to a tiny minority; but there are several lines of evidence to suggest that the ability to raise significantly above-replacement numbers of surviving children was (in most historical times and places) restricted to a small minority of men. One in eight seems not-implausible.

    By contrast, the average number of surviving children for the majority of men was probably somewhere between zero and one – despite that they were having sex and babies.

    • MawBTS says:

      By contrast, the average number of surviving children for the majority of men was probably somewhere between zero and one – despite that they were having sex and babies.

      Pardon the question, but how did you arrive at this number?

      In sub-Saharan Africa we see huge families of 4-5 children, even in impoverished regions. Why would a feudal peasant in Lancashire find it harder to have kids than a subsistence farmer in the Horn of Africa?

      • ursiform says:

        During the Ethiopian famine in the 80s Ethiopia managed one of the highest population growth rates in the world. Hundreds of thousands starved to death, millions were born.

      • Dale says:

        I want to note that “4-5 children” is not huge by historical standards. J.S. Bach was one of eight children (of one mother) and Queen Victoria had 9 children.

      • mossrichjals says:

        In sub-Saharan Africa we see huge families of 4-5 children, even in impoverished regions. Why would a feudal peasant in Lancashire find it harder to have kids than a subsistence farmer in the Horn of Africa?

        He didn’t. Both areas had large families for a variety of practical reasons. In the absence of a food or material surplus, children are not only extra producers of output via the farm or herd, but over time serve as an old age insurance in that they take care of or help their parents. Elsewhere near Lancashire, in Northern Europe, the Irish were known for their large families.

        • MawBTS says:

          Yes, that seems key. A child’s only a fitness burden until about 6-7 years of age, then you gain an extra laborer that you don’t have to pay. And if it’s a girl, you can hope for a favorable union with a man of means – thus winning the Spamalot version of the lottery. And the more kids you have, the more lottery tickets.

          Many children throughout the world (especially in China) are growing up with parents who look on their offspring as investments. One way or another, they will be expected to repay the cost of their upbringing with compounded interest.

    • gcochran9 says:

      “By contrast, the average number of surviving children for the majority of men was probably somewhere between zero and one – despite that they were having sex and babies.”

      Fuck me, that’s obviously ridiculous. In real life, take a peasant village in England: if your model were correct, you’d have surname turnover every couple of generations. But that didn’t happen.

      Here’s a model that’s at least in the ballpark: there was some class differential in fitness. The poorest, landless laborers, had a TFR below replacement, but not by a tremendous amount: 1.6? Most peasants were close to break-even, upper farmers did better than break-even, Other groups were mostly too small in number or too urban (population sinks) to matter. Overall TFR was of course break-even over the moderately long haul, in a sloppy way, with occasional epidemics and crop failures.

      • peppermint7889 says:

        I don’t know how anyone can ever believe that only ⅓ of men reproduce when they went to school with kids who had parents. But there are a lot of men today who have only 1 kid. I’m guessing most men have 1 or 2; maybe some government statistics somewhere can be mined for a histogram.

      • Bruce Charlton says:

        @Greg – You really should learn to argue about (or, preferably, discuss) principles sometimes – stick to the point at issue, avoid quibbling over inessential precision etc . In these discussions, numbers are always approximate, and always will be.

        Such rhetorical tactics are intellectually disreputable and self-corrupting when engaged in habitually. I mean it.

        The real discussion is about the relative importance of fertility compared with child mortality rates in determining reproductive success.

        I really cannot understand why you should so consistently avoid engaging this extremely important point – but I herewith give-up on trying to communicate it to you.

        • gcochran9 says:

          The example you suggested was crazy. Do it again and I’ll call it crazy again. I think you don’t know anything at all about this.

          In most circumstances, typical Malthusian circumstances, neither fecundability nor child mortality determines population growth. On average, every human population is capable of producing lots of children, ten or more, and thus population can increase very rapidly when people choose that path and have no other limiting factors (such as disease or limited resources). See Amish, or colonial Americans.

          If you had six kids in medieval Europe, in typical circumstances, four didn’t make it, due to disease or insufficient food. If you were a typical peasant, having 10 wouldn’t help: you could still only feed about two. If you lost more than usual to disease or famine, you could usually catch up later, since people are capable of having far more than that six, and since most child mortality happened fairly early in life (which means that you hadn’t invested that much of your very finite resources into them). The rich did worse than you would expect: living in towns and cities was dangerous. If you were a Lancastrian or Yorkist, your life expectancy wasn’t good either… Still, the upper middle classes probably exhibited population growth, the landless had sub-replacement fertility (but not drastically so).

          The question is whether there was ever a society in which only a small fraction of men fathered children. Or you could phrase it differently, say one in which a small fraction of men father the great majority of children.

          We have to define “small fraction” Was there ever a society in which half of the men fathered 3/4ths of the children? Yes: not even unusual. What about one in which half of the men never had any children: fairly extreme – might possibly be true of some polygamous regions of sub-Saharan Africa. But obviously not the case in Europe, or China: we have records.

          In most of the cases we know, reproductive differences between different economic classes were not too big, although they could exist. If they had been very big, you’d see fast turnover. They would be a new set of last names for the people in the less successful classes every couple of generations – didn’t happen.

          Was there ever a situation in which only 1 in 17 men had children? No. That’s crazy talk. How about one in which 1 in 17 men accounted for the majority of births? Never happened.

          You can have a situation in which a particular subset of the population outbreeds the population as a whole – for a while. Ashkenazi Jews were 1% of the population of the Polish-Lithuanian Commonwealth in 1500 and 10% in 1800: they averaged about 3 kids. Polish nobility took about the same path, and they too were something like 10% by 1800. Of course growth stalled out: the marginal Ashkenazi Jews were now peddlers, the marginal Polish nobles were now farmers with a famous last name.

  2. Matt says:

    One previous interpretation of these patterns was a period of large scale polygyny. But it seems to me this is a less persuasive argument than pervasive father-son and to a lesser extent uncle-brother advantages.

    Looking at their figures in their paper, between S4A and S4B and Table S4 (as reposted on Dienekes blog entry – http://dienekes.blogspot.co.uk/2015/03/bottleneck-in-human-y-chromosomes-in.html)

    Europe seems to dip slightly more than the Near East (3000 BC, around the time of Corded Ware and post-Corded Ware culture vs 5000 BC in the Near East) a little later then then expand in diversity more. The Near East dip is still well after the first farmers though.
    East Asia shows a greater long term size of male lineages, and less of a dip than Europe, overall. It also expands less. The dip there is timed between the European and Near Eastern one, closer to the European dip.
    Overall male-specific effective population size is highest in the Near East now – the dip was earliest there as well, but there is no regional relationship between time of the dip, size at time of dip and level of modern variation.

    Europe has seen the largest magnitude of change since the dip, suggests it changed more than another other region from having high male reproductive variance to low (makes sense it terms of how star like the main European y lineages are).

    Male effective population size, to-day, is lowest in Central Asia followed by Africa.

  3. If it is your job to correct bad science reporting you sir have job security. Can you imagine that poor first farmer with 17 wives, he never could have left his hut for the fields.

  4. RCB says:

    Is there an N_e model in the literature for a process like this? I.e. sex-specific, culturally-transmitted inheritance of fitness?

    • gcochran9 says:

      I haven’t seen it, but that’s pretty obviously what happened with Genghis Khan and the Golden Family. And the Manchu, and the descendants of Neill of the Nine Hostages (himself R1b). It’s not hard to model.

  5. Dale says:

    I haven’t modeled it, but it seems that for there to be a strong reduction in Y-chromosome diversity without much reduction in autosomal diversity, the culture must have a strong tradition of patrilineage. Which is true of a lot of cultures.

  6. j says:

    Slate’s article suggests that only 1 man in 17 effectively reproduced and in the very long term that is so. The “journalist” aimed to exploit this piece of data to write something that would attract attention, that is clicks. Maybe she is paid by clicks like Steven Sailer at Unz. The famous car-wash video clip would have served well in her quest for clicks.

    I cannot dispute your suggestion that the strong reduction in Y-chromosome diversity without much reduction in X-chromosome diversity is consequence of bloody wars. The Bible documents those events, as well the Quran and some Nordic sagas. I only wish to suggest that in the last centuries the same process continues – sans massacres. In Western societies the percentage of females that has children is always higher than of males. While females around 35 – 40 get desperate to get pregnant, males are indifferent. Sperm banks have difficulties to recruit donors, and they have to pay royally to get men to donate. The fact that females pay to the banks even more reflects that it is not so easy for a woman in our society to get laid by a middle class professional. I see in the office the competition for any potential father – single or married. I could mention also homosexuality, that knocks out maybe 5% of males from the ranks of the reproductors. To save you the ink for “You are wrong” or “you are crazy”, I’ll admit beforehand that I may be wrong.

    • gcochran9 says:

      ‘1 in 17’ – It is not so. Nothing like that, anywhere.

      True that Amanda Marcotte should have put in that YouTube video of Joy Harmon washing the car in front of the chain gang.

      Although Slate hires worms, that’s not the problem: the researcher told a number of reporters the same confused thing.

      • j says:

        Sir, to make myself even more odious, I’ll point out that male gangs massacring vanquished males and raping the females have become rather scarce lately. There is not one documented case in the Western world of a male gang lkilling off the males of the neighboring village and raping the females. In my opinion the rate of homicides and rapes are exceedingly low in Western (and East Asian) societies. It is possible that the stories of the Bible, theQuran, the sagas, are … phantasies, just literature. The current anti-rape hysteria everywhere is based on phantasies. I believe that a girl wishing to be raped today has to drink to pass out and lay down on bed in a male fraternity, with the legs wide open. And she may not succeed.

        • Greying Wanderer says:

          “There is not one documented case in the Western world of a male gang killing off the males of the neighboring village and raping the females”

          You don’t need to kill the other males though. The gang ruled parts of the urban blight are similar to this in that the most violent males form into a group and effectively claim the young girls coming up in their patch. Other males are kept away by the threat of violence or violence that falls short of killing.

          They basically herd the females.

          It’s not absolute because
          – they only claim the most attractive 1/2 or 1/3
          – the preferred age range is teen
          – they mostly lose interest after a girl has had one kid.

          As status comes from the number of girls who’ve had one of their kids rather than the total number of kids that means there are plenty of females still available
          – less attractive teens
          – older i.e. 20s
          – already had a gang member’s kid
          otherwise I don’t think the majority of non-gang males would put up with it.

          So although I think the massacre thing happened as well, you can get the same effect over multiple generations with something less drastic, especially if attractiveness ~ health and fertility.

          An historical example of this might be aristocrats and their droit de seigneur.


          So a lot of the time maybe you start with for example 90 ydna C and 10 ydna G and n generations later it’s become 10 ydna C and 90 ydna G.

        • setstamov says:

          ” The current anti-rape hysteria everywhere is based on phantasies.” – Then what did Boco Haram do to all those 274 girls and women that they kidnapped on April 14th, 2014 from Chibock? (of course, they killed the men from the village first – at least those that did not obey to the new rules – which were “kill everyone and rape the women”. Otherwise you are right. But I doubt that nearly biblical proportion of the event is a singularity in human history.

          • Toddy Cat says:

            “There is not one documented case in the Western world of a male gang lkilling off the males of the neighboring village and raping the females.”

            Does the Red Army of 1945 count as a “male gang”, and does Berlin count as a “neighboring village”? It’s all in the definitions…

        • mossrichjals says:

          You sure about that no documentation thing? To the contrary, there is plenty of documentation. The Vikings were known to often kill men and take their pick of the women when they raided various coasts of Europe. In fact the Vikes retained the females they wanted and sold the rest, relying heavily on female captives for both sexual and reproductive work. The medieval traffic in slaves was overwhelmingly a traffic in women. (Bennett J, Medieval women in modern perspective. 2015 in Women’s History- a Global Perspective vol 2, 2015).

          If the killers are an armed force dispatched under a particular political authority, you are wrong as well. After the battle of Leuctra, 371 BC, the Thebans became undisputed masters of Boetia, and burned the city Orchomenus to the ground, killed all the male inhabitants and sold the women and children into slavery.


  7. j says:

    The scenario of Western Hunters massacring males and raping females in prehistory may be phantasy. You dont need violence to produce the 1 to 17 (or whatever) relationship detected..

    • Greying Wanderer says:

      If lactose tolerance went from 1% to 70%+ along the Atlantic coast then maybe all they needed was the ability to get off their horse and drink their milk.

  8. dearieme says:

    Here’s an empirical fact for your amusement. I’ve found that whenever I mention on the web that Neill of the Nine Hostages’s mother was Anglo-Saxon, irate, racist Irishmen respond saying that it can’t be true. But insofar as anything in the Dark Ages can be taken as true, it is.

  9. The fourth doorman of the apocalypse says:

    And that’s only in the mitochondrial DNA, I am sure:

    Wayne established that every dog’s mitochondrial DNA is 99.9% the same as a gray wolf’s — so close they are the same species. One-third of that 0.1% difference is in the genes for fat and carbohydrate digestion. Half is in the brain and the tiny remainder — so little it surprised even Wayne — controls the time and rate of physical development and accounts for the vast differences in size and shape between breeds. Basically, dogs are wolves that adapted to eat rice and be nice.

    It’s amusing when they try not to be morons.

  10. Bultare says:

    Y-chromosomes are not equal and that probably explains half of things, with Conan being the other half.

    There seems to be a trend of K2(ancestor of R,N,O,Q and a few others) supremacy over other haplogroups throughout Eurasia. Genghis Khan did a good job spreading his branch of C, but what if it was all for nothing and it’s doomed to once again lose ground to K2?

  11. Ilya says:

    Sorry, I’m asking an off-topic question. But I just have to. I am referring to a recently published results on CRISPR, referred to

    So, we have the CRISPR methods that allow one to modify one of the chromosomes in the pair of some organism. We’ve all head of that. However, the article describes a method based on CRISPR to modify both chromosomes on the pair simultaneously (thus making the carrying organism/embryo homozygous for that gene).
    Still, one would expect that, in case of crossing of the above organism with a second one, which (for the sake of the thought experiment) might be homozygous for a different allele on the same locus, that we’ll get the offspring to be homozygous on the first allele with 25% probability, according to Mendel’s laws of inheritance (and 50% as heterozygous).
    But apparently, that’s not the case here… The actual probability of the offspring being heterozygous on the first allele (effectively, a “super allele”) is a whopping 97%! Meaning that heterozygocity likelihood is < 3%…

    The thing that’s unclear to me is how they achieved the ability to override the contribution of the other parent’s gene.

    Question 1: Is it because of the new allele’s inherent characteristics? Or is it because CRISPR added some “payload” molecules that will propagate the “yellow” gene to perpetuity?

    Question 2: Also, I’m struggling to find any examples of where being a homozygote would confer any direct advantages to humans, if anyone thought of applying this to humans in future.

    I’d welcome anyone’s input/opinion on that. Especially, Dr. Cochran’s.

    • Ilya says:

      Change: “The actual probability of the offspring being heterozygous on the first allele” to
      “The actual probability of the offspring being homozygous on the first allele”

  12. ohwilleke says:

    I’ll add another voice to the likely importance of child mortality. In the absence of contraception, lifetime children per woman averages somewhere around eight per lifetime. There are long stretches of time where populations were barely above replacement. The “state of nature” for human child mortality is ca. 75%. Slight tweaks up or down from 75% with social class make a huge difference over a dozen generations, and lots of factors can generate those kinds of tweaks.

  13. The fourth doorman of the apocalypse says:

    Kinda OT here but I am looking for some good books/literature on the topic of the evolution of religious inclinations among humans. Basically, expensive signalling doesn’t do anything for me so I am looking for other ideas.

    • The Monster from Polaris says:

      If you’re interested in currently on-going evolution, take a look at Eric Kaufmann: Shall the Religious inherit the Earth?

      At the rate certain religious groups are breeding, they can be expected to consitute a large fraction of humanity some centuries from now, regardless of whether they have any success in proselytizing.

      • JayMan says:

        @The Monster from Polaris:

        That’s assuming the current fertility pattern remains unchanged until then, when there’s absolutely nothing demanding that that will be the case.

        • The Monster from Polaris says:

          There is, at least among Conservative Laestadians. Their dogma makes it clear that it’s their duty to bear as many children as possible, so that souls waiting to be born can be accommodated.

          Of course, even religious dogmas can change, but they do tend to be rather resistant to change. Moreover, if we imagine a situation where some Laestadians start questioning that dogma while others remain faithful to it, the latter group is likely to become dominant simply by outbreeding the former.

          It’s simply evolution in action — mainly cultural rather than genetic evolution, but the result is likely to be much the same.

          I hope I’ll be proven wrong, but the situation doesn’t look good.

    • The fourth doorman of the apocalypse says:

      Surely there has to be something better than this:

      The key, argues Wilson, is to think of society as an organism, an old idea that has received new life based on recent developments in evolutionary biology. If society is an organism, can we then think of morality and religion as biologically and culturally evolved adaptations that enable human groups to function as single units rather than mere collections of individuals?



      • setstamov says:

        Wilson has been referring to H. Spenser’s notion of “superorganic”. Spenser is the guy who first employed terms as “fitness” in its contemporary meaning, so I guess we own him some respect; unfortunately, just as his contemporary, Darwin, he was not a mathematician and I doubt Spenser’s arguments about group selection would stand today. However, if one day in the far future 1/17 (or less) of the men father all children (say homosexsuality +cellibacy picks to 99% of living male population), Spenser’s and the two Wilsons theories might become evolutionarily stable realities and then humanity would make the turn that ants once made.

    • The fourth doorman of the apocalypse says:

      This looks more interesting:

      Click to access Bulbulia–EvoPsychRel.pdf

  14. John Hostetler says:

    Greg, their mistake seems to stem from this, in the WaPo article:

    “For every 17 women who passed on their DNA, researchers could find genetic evidence of only one male whose lineage stretched to modern times.”

    It seems someone has conflated ’17 times more mitochondrial lineages than Y-chromosome lineages still survive from that time’ with ’17 times more women than men at that time reproduced.’

    Of course WE know it’s not the same thing at all, but when you only have a gazillion-dollar budget like Slate, whaddya gonna do?

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  17. Yeyo says:

    1 in 17 is ridiculously high though polygyny was probably far more common than today. We can get a clue by looking at patterns of violence. Widespread polygyny results in lots of single men who go on wars and raids, bronze age Scandinavia springs to mind, do we have any data from there?

    • gcochran9 says:

      What little we know [from linguistics] about Indo-European society suggests that it was monogamous, but who knows? it is certainly the case that some of the historically documented societies in Europe were monogamous before Christianity: the Greeks and Romans, for example.

      • Yeyo says:

        Not denying that, since most of the new rules implemented by the church were simply roman customs. It’s possible they helped erasing remnants of polygamy among the ruling classes across the rest of the continent as well.

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