Why Genghis Khan won’t have had 16 million descendants.

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Last Thursday, I posed the mystery of whether there are in fact 16 million direct male descendants of Genghis Khan. This factoid came from a 2003 study of some 2000 Central Asian men, of which 8% were found to share a common male ancestor around the year 1000 AD, give or take a century.

The adherents of this factoid basically point out what a stud Genghis Khan and his sons were. He had many wives himself and some of his sons and grandsons shagged everything they could lay their hands on in the territories conquered by the Golden Horde  led by his grandson Batu Khan. Some of them, like Kublai Khan, would easily have had hundreds of sons and Genghis himself probably had dozens.

The first hint of doubt that you should have is this whole business of the direct male line and what that implies: if you believe that 8% currently is directly from Genghis then you by implication believe they were not by his 3 brothers  and 2 half-brothers, who also were high-up in the Mongol hierarchy. You by implication believe they were not by the many uncles on his father side, nor indeed from any of the Mongol men who will have had the same male ancestor as Genghis Khan earlier in the line. You see, the Y-Chromosome attributable to Genghis is close to the one of his own father, his grandfather, his great grandfather, etc. You basically have to believe that there are relatively large and unusual genetic differences between his Y-chromosome and that of all the other male offspring of his own male ancestors to pick him as the sole source. Only then could you say the 8% were his and not the result of himself and a whole group of male  Mongols who shared a very similar Y-chromosome of an earlier male ancestor. Just on the genetic side, the odds of such a thing are pretty slim already.

Consider how many male Mongols you would thus have to ‘wish away’: Genghis came from an important family. Up his family tree were prolific male shaggers. What are the odds then that the contribution all the other men coming from the same male line would be outside the 8%? Miniscule, absolutely miniscule.

Consider further how little Genghis could actually himself have done during the conquest of the Khwarezmian Empire around 1219. Yes, he apparently reserved the most beautiful women for himself. But he led an army of up to 250,000 men, all raping and siring as well. Now, I don’t care what kind of super-stud Genghis was and how often he got first dibs on the prettiest women: he will not have been able to out-shag his fellow conquerors by much more than a factor of 10 (at best). Yes, he will have had many more women, but he will have had them once, whereas all his commanders and soldiers would have taken wives and concubines and looked after them for years, protecting the sons that came from those unions.

Consider moreover how the male descendants of Genghis would have been treated. Certainly his official sons had great status and protection. But any son he bore as a result of rape or one-night arrangements will have subsequently stood out like a sore thumb: the women would go back to their families and get other men who would not have looked kindly upon raising the son of someone else. You can be sure that many an illegitimate son of Genghis would have met an unfortunate and untimely death. It thus seems very likely that all the ‘illegitimate’ sons of Genghis would have had much less further genetic success than the average male in that time. The same goes for all the other illegitimate children of the recognised direct off-spring of Genghis.

It is this aspect of no special treatment for all but the recognised off-spring of Genghis that is crucial: the average male around at that time has 10 to 20 living male ancestors now. In order to get a higher success rate one needs some real advantage. For Genghis to have had 16 million if all the illegitimate ones had no special procreation advantage (and quite likely a big disadvantage) truly means that he and his recognised male offspring must have personally sired close to a million sons in that era. That is just beyond all reason. Even if 5 generations of his official descendants shagged themselves silly day and night, they couldn’t get close to that kind of number.

The only remaining possibility would then be that there was something special about Genghis’ chromosomes giving him and all his male descendants a true advantage in terms of procreation, even if they were illegitimate and had no help in terms of wealth or position at the start of life. That would not only imply that the current human race has supermen amongst it with some advantage that one should be able to measure, but in order to attribute them to just Genghis you then still need to believe this distinct true advantage was due to a mutation when the Y-chromosome was copied from Genghis’ father to Genghis himself. Very, very far fetched.

Put all this together and think of what happened in that time: up to 250,000 men raiding through Central Asia, making examples out of whole cities by slaughtering everyone and occupying huge territories with a population in the tens of millions. To the victor the spoils, with all the desirable young women married to or raped by the Mongols and their allies, of which Genghis Khan was but a single man. And the other men in the region of course were not all dead either, so it is not just the other 250,000 that vie for the 8% supposedly starting with Genghis. Various other waves of conquerors have swept through the region since.

What are the odds that Genghis Khan and his direct male descendants then managed a whole 8% for themselves? Or even Genghis Khan and his 10 closets male relatives? I would say pretty slim. What, on the other hand, are the odds of a fairly large slice of the Mongol horde managing 8% for themselves as a block of men? Pretty good, you would have to say.

What does this mean? Well, it means that the common male ancestor of whom 8% of all East Asian men derive is most likely not Genghis Khan but rather a male ancestor further up in his male line and the male line of a whole slice of Mongol men. Some guy living around the year 1000 or even earlier who will, by the time of the Khwarezmian Empire and the Golden Horde that swept through East Asia, had hundreds or thousands of male descendants in prominent places in the Mongol genetic pool, poised to take advantage of the raping and other female-acquiring possibilities that came with that massive conquest.

You should hence not be surprised to know that after writing this I was alerted by my research assistant Miriam Carter to two genetic studies doubting the 8% number, though purely on the basis of genetics. A 2012 study by Russian geneticists suggests the direct male descendants of Genghis Khan have all but died out (which I don’t believe either). Perhaps more importantly, another study (Abilev et al. in Human Biology 2012) attributes the 16 million to a whole tribe currently living in Kazachstan, the Kerey, who functioned as elite units in the Mongol armies and were indeed exceedingly well poised to spread their genes around during the Mongol conquests. That tribe and the Khan family were close so it is possible that the earlier male ancestor spawned both the males from the Khan family and much of the Kerey.

One has to wonder whether the authors of the original study were fully aware of how unlikely it was that Genghis Khan was really the direct male ancestor of the 8%. After all, they labelled their study ‘The Genetic Legacy of the Mongols’ and not ‘The genetic legacy of Genghis Khan’. In their study they are furthermore quite careful to acknowledge that their best-guess for the period in which the common male ancestor lived was the year 1000, not the year 1200 which was when Genghis Khan was still around. He is on the outer fringes of their confidence bands. Yet, the authors do say explicitly that Genghis Khan fits the bill for the kind of person they are looking for and it is that what was taken up by the world’s media. The factoid that went into the world media certainly helped to get more attention for their study. It made their careers.

So, once again champagne for the many who had similar doubts. Diet water for the rest.

3 Responses to "Why Genghis Khan won’t have had 16 million descendants."
  1. I did some back of the envelope calculations and I found that ghengis and every one of his descendants will have needed to have on average ~1.5 sons (or three kids) per generation to have 16 million descendants. This assumes that he was born in 1162 and his lineage procreated once every 20 years. I’m not very confident in these results as they were done on the move.

  2. Matthew,
    The difficulty in seeing whether the 16 million is realistic is finding a way to count the likely lineages. Taking an ex ante approach would ignore actual circumstances, ie how do you know that 1.5 is reasonable all those generations? Centuries of plagues and wars combined with eras of prosperity. Its virtually impossible to say 1.5 is reasonable without truly going through the circumstances of every generation along the way. Forget it.
    One has to find another way to count them.
    The ‘trick’ I employ is to separate the lineages of the legitimate and the illegitimate and then relate them to what happened to the average lineage. That way I don’t have to argue whether 1,5 is realistic in the 18th century or other periods but can use the fact that we know the average population increase over that long period.

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