Is one in two hundred men a descendant of Genghis Khan?

Question

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?

EDIT:

Link to the original paper (pdf)

Answer 1

I love it when questions contain the research for their own answer.

The paper describes a particular set of genes:

We have identified a Y-chromosomal lineage with several unusual features. It was found in 16 populations throughout a large region of Asia, stretching from the Pacific to the Caspian Sea, and was present at high frequency: ∼8% of the men in this region carry it, and it thus makes up ∼0.5% of the world total

It analyses it current populations statistically, using a couple of approaches to conclude:

The origin was most likely in Mongolia, where the largest number of different starcluster haplotypes is found (fig. 1). Thus, a single male line, probably originating in Mongolia, has spread in the last ∼1,000 years to represent ∼8% of the males in a region stretching from northeast China to Uzbekistan.

It considers, and shows evidence to refute, a number of possible causes of this, e.g.

Could biological selection be responsible? Although this possibility cannot be entirely ruled out, the small number of genes on the Y chromosome and their specialized functions provide few opportunities for selection (Jobling and Tyler-Smith 2000). It is therefore necessary to look for alternative explanations.

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.

Answer 2

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:

N   g             generation period (800 / g)
1.5 42.4616264022 18.8405406901
1.6 36.6310106312 21.8394192848
1.7 32.44589391   24.6564327128
1.8 29.2907426583 27.3123836201
1.9 26.8234068696 29.8246976564
2.0 24.8384591649 32.2081170449
2.1 23.2050698916 34.4752247564
2.2 21.8359404137 36.636846632
2.3 20.6705719334 38.7023640457
2.4 19.6657027316 40.6799599749

the table is generated using the following python program:

>>> for i in range(15, 25, 1): 
...     g = log(0.005 * 6000000000) / log(i / 10.)
...     print i/10., g, 800 / g

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:

1. That GK and his male relatives has a large harem, and the recent global trend to have a smaller family unit.
2. That as the world's population is saturated, it will be more and more difficult to find a non-Genghis Khan descendant to marry to. This effect can be be modeled using logistic function, but given that the final value (0.5%) is relatively small, the difference between the logistic function and the related exponential function would not be significant (a logistic function is an exponential growth with an upper bound; given the same starting condition they start closely but will quickly deviate above 10-30% saturation, our target value 0.5% is well below that).
3. The descendants of a descendant that does not intermarry may intermarry.