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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)

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"Trick to get their paper published" - One would expect from proper peer review that gimmicky exaggerated claims would not get published. A simple "order of magnitude" calculation that would take into account the total number of earth's inhabitants at a given time allows you to roughly estimate how many ancestors there are. –  Lagerbaer Aug 13 '11 at 0:28
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I cannot comment the exact genetic lineage of Genghis Khan, but a few years ago I read this piece from John Allen Paulos abcnews.go.com/Technology/story?id=2019650&page=1 . He claims that a genetic line(Jesus for shock value) either dies out fast in a few generations or grows a lot. So if there are descendants of the mongol ruler there will be lots of them. So it is plausible. –  Daniel Iankov Aug 13 '11 at 1:06
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@Lagerbaer “One would expect from proper peer review that gimmicky exaggerated claims would not get published.” – You wish! Alas, it’s all too common. Authors try to pimp their papers by whatever way possible to get into a high-profile journal and all too often reviewers don’t care enough to filter this out. –  Konrad Rudolph Feb 15 '12 at 23:09
    
There was a segment on QI which states: "Mathematically speaking, everyone in Europe is related to Charlemagne. This is because everyone has two parents, four grandparents, eight great-grandparents and so on. By the time you get to the 13th century, you have more direct ancestors than have ever been human beings - about 80 billion." –  coleopterist Oct 4 '12 at 20:24
    
The claim they make in the paper is a lot stronger than just being descendants. They claim that 8% of asians are descendants of Genghis Khan through the male lineage. That means in practice that they claim that >90% of human are descendents of Genghis Khan if you would say that you are a descendent of your grandmother. –  Christian Oct 5 '12 at 9:38

2 Answers 2

up vote 23 down vote accepted

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.

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Note: if the research is done with Y chromosome only, it limits descendency line to male only. Such limiting leads to interesting statistical effects, like en.wikipedia.org/wiki/Y-chromosomal_Adam. –  Suma Aug 15 '11 at 9:09
    
@Suma, could you please elaborate? I skimmed that Wikipedia article, and didn't see any "interesting statistical effects" (unless you mean the concept of Y-chromosomal Adam, itself, which hardly affects the legitimacy of this paper.) –  Oddthinking Aug 15 '11 at 10:08
    
Yes, I mean the concept itself. The "interesting statistical effect" is that whenever you take a feature which is inherited by a male only or female only line, you will always end with something like a "single common ancestor" (Chromosomal Adam, Mitochondrial Eve) when looking far enough into the past. This is because such features can only disappear (and never appear again). Whenever the populations meet and breed, you will see something like this. That said, I admit I did not read the paper and I do not know how this affects its validity. –  Suma Aug 16 '11 at 10:41
    
@Suma, this is basically the subject of the paper - whether the Chromosomal Adam lineage for this particular sequence passes through Khan. It doesn't affect its validity so much as form the essence of it. –  Oddthinking Aug 16 '11 at 12:36
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It only establishes that 8% are descendent of Mongol folks that were related by paternal lineage to an ancestor of Genghis Khan--- not that they are descended from him personally. For this, you would need Y markers unique to his specific descendents, and look for their prevalence, and this is exceedingly difficult. –  Ron Maimon Oct 7 '12 at 16:55

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.
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Answers should be referenced. We do not accept "logical" answers. See meta: meta.skeptics.stackexchange.com/questions/1019/… –  Ebenezer Sklivvze Aug 13 '11 at 7:03
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Of course, 30 years per generation is an exaggeration from modern times. Sixteen to twenty years is a better approximation. Call it 20 to be fair, that gives us 2^40 ≈ 1.1 x 10^12, or 16,200% of the world's population are descendants! Now, remind me again why speculation is not accepted on Skeptics.SE :-) –  Oddthinking Aug 13 '11 at 7:34
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@Oddthinking: Your argument is flawed since as problem #2 stated: "as the world's population is saturated ...". To be more rigorous, when the population is saturated, the growth function is no longer exponential, instead it becomes Logistic Function. In any case, my calculation is a lower bound, so it still answers the question that the number 0.5% is definitely not unreachable (given the appropriate circumstances, such as no genocidal targeting only Genghis Khan descendants or Sudden Generation Death Syndrome). –  Lie Ryan Aug 13 '11 at 7:52
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@Oddthinking: I think you'd agree that I can trivially prove that it is impossible for a person (with normal birth rate expected of a human) born in 1950 to have 1000000 descendant by 2000. That's just implausible. However, it is plausible for that person to have 30 descendants; although I do not necessarily claim that that person actually makes 30. If we extend such calculation over 25 generations, we can show that 0.5% is plausible for people living in GK's time, although not necessarily proving that GK actually do has 0.5%. –  Lie Ryan Aug 13 '11 at 8:36
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@lie I am opening a discussion on meta about this. meta.skeptics.stackexchange.com/questions/1080/… –  Jeff Atwood Aug 14 '11 at 9:56

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