I've read years ago that 8% of all Asian men and thus 0.5% of all men would be descendant of Genghis Khan.
Is there any truth to this? Or was this some trick to get their paper published?
Link to the original paper (pdf)
I love it when questions contain the research for their own answer.
The paper describes a particular set of genes:
It analyses it current populations statistically, using a couple of approaches to conclude:
It considers, and shows evidence to refute, a number of possible causes of this, e.g.
It searched for confirmatory evidence by looking at a population that are (putatively) direct male line descendents of Khan.
Looking through Google Scholar, I can see no examples of refutation, but many others citing their results positively (e.g.). The paper was published in a reputable peer-reviewed journal, and contains a number of authors from prestigious institutions that are working within their areas of expertise, so the idea that it might be exaggerated for publication is unlikely.
It appears to have a robust result, that it seems reasonably to provisionally accept unless counter evidence is produced.
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Let's work out whether the number mathematically makes sense. Genghis Khan has a large family, a long family line, and there are history of interracial marriage and the Mongols often raped people that they conquered. The Mongols campaign reaches a large part of Asia, Europe, and Russia. Therefore, we will assume that his descendants are not geographically or ethnographically isolated.
Assuming that the average "generation" is 30 years and Genghis Khan lived ~800 years ago, then an average Genghis Khan's descendant will be in their 25th generation.
Assuming that in each generation, for each Genghis Khan descendant there are two of their children that will intermarry with someone that is not a Genghis Khan's descendant, then there are 2^25 ≈ 30000000 Genghis Khan descendants or roughly 0.5% of the world's population.
While the model are rough and the approximations are coarse (and yes, I engineered the numbers to get 0.5%), the numbers could work out so the number 0.5% is not unreasonable.
How do I get this number?
It can be worked out backwards, if 0.5% of the world population is a Genghis Khan's descendant, then if N is the average number of a GK descendant's children that marries a non-GK descendant, and g is the number of generations needed to reach 0.5%, then assuming the growth follows the exponential function, it follows that N^g = 0.5*6000000000. There are a range of possible N and g that satisfies this:
the table is generated using the following python program:
All the numbers in the table fell within a fairly reasonable range that you would expect (I picked N=2 in the above answer since it's a round number), so I concluded that the paper's claim that 0.5% of the world population is a GK descendant is not necessarily exaggerated, i.e. it is plausible.
What this model does not take into account:
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