The short answer is that nobody knows exactly, but the most cited modern estimate is that somewhere between 8 and 16 million men alive in 2003 — about 8% of men in the region of the former Mongol Empire — carry a Y-chromosome haplotype that is consistent with descent from a single male ancestor who lived around 800 years ago, and that the most likely such ancestor is Genghis Khan. The figure is real, the interpretation is contested, and the number has been revised down by later studies.
The 2003 Study
The headline finding comes from a 2003 paper by Tatiana Zerjal and 17 co-authors at the University of Leicester, published in the American Journal of Human Genetics (Zerjal et al., 72, 717–721, 2003). The paper identified a Y-chromosome haplotype — a particular pattern of mutations on the male sex chromosome — that was present in about 8% of men in a sample of more than 2,000 men from across Eurasia. The haplotype was strikingly concentrated in the region of the former Mongol Empire (Mongolia, Manchuria, the Caspian region, Central Asia), and was most common in Mongolia itself, where 25–30% of men carry it.
The paper’s central inference was that the most likely explanation for the pattern was a single male ancestor who lived around 800 years ago — that is, around 1200–1300 CE — and who had an exceptionally high number of descendants. The paper did not claim to prove that the ancestor was Genghis Khan; it argued that Genghis Khan was the most plausible candidate, given the dates and the geography.
The Controversy
The Zerjal et al. paper was controversial from the start, and the controversy has not gone away. Three classes of objection have been raised.
First, the dating: the estimate of “around 800 years ago” is necessarily approximate, and could fit other major Mongol-era founders, including Jochi, Chagatai, or Ögedei. Several critics have pointed out that the ilkhanate and the Golden Horde ruling classes also produced Y-chromosome lineages of this kind, and that the Genghis-Khan-specific identification is, at best, a best guess.
Second, the haplotype identification: a 2007 paper by Miroslava Derenko and colleagues and a 2011 paper by Boris Malyarchuk have argued that a non-trivial portion of the Zerjal haplotype is in fact derived from non-Mongol sources — for instance, from the Qin and Han Chinese populations of the 2nd–1st centuries BCE — and that the Mongol-era expansion is smaller than the Zerjal estimate suggests.
Third, the social-selection hypothesis: an alternative explanation for the spread of any elite male haplotype is not the number of children a particular khan had, but the social premium on being descended from him, which led to a long-run advantage in reproductive success across many generations. This is broadly compatible with the Zerjal result, but it weakens the “Genghis Khan had thousands of children” version of the story that has become common in popular accounts.
The Geographic Distribution
The distribution of the haplotype is broadly consistent with the territorial extent of the Mongol Empire, and most concentrated in Mongolia itself (about 25–30% of men) and in the Central Asian populations that were politically subordinate to the Mongol empire (5–10% of men). The haplotype is also found in low but non-zero frequencies in the regions of the former Yuan Dynasty, the Ilkhanate, the Golden Horde, and the Chagatai Khanate.
A separate, smaller, similar cluster of Y-chromosome lineages is found in the Manchu population and is associated with the Aisin Gioro imperial house of the Qing dynasty. It is a parallel phenomenon — produced by a different elite lineage in a later period — but it confirms that elite male reproductive advantage is a real demographic pattern in the region.
The Implications
The genetic legacy of the Mongol Empire is a real and documented phenomenon, and the 8% / 16 million figure is a reasonable summary of the Zerjal et al. result. It is not a settled count, and it should not be cited as a precise number. The honest modern statement is: roughly 1 in 12 men in the region of the former Mongol Empire carries a Y-chromosome haplotype that is consistent with descent from a single male ancestor who lived around 800 years ago; the most likely such ancestor is Genghis Khan; the actual identification is not proved; and the social-selection mechanism is at least as plausible as the reproductive-capacity mechanism.
Sources
- Tatiana Zerjal et al., “The Genetic Legacy of the Mongols,” American Journal of Human Genetics 72 (2003): 717–721.
- Miroslava Derenko et al., “Distribution of the Male Lineages of the Y-Chromosome Haplogroup C in the Populations of Eastern Eurasia,” Russian Journal of Genetics 43 (2007): 840–848.
- Boris Malyarchuk, “The Y-Chromosome C3* Star-Cluster Attributed to Genghis Khan’s Descendants Is Present at High Frequency in the Kerey Clan from Kazakhstan,” Human Biology 83 (2011): 109–117.