The Y-chromosome is one that geneticists love to study. Because it is passed on from father to son with no matching chromosome to confuse the issue it’s possible to study lines of descent in a much more direct way than is usually possible. Mitochondrial DNA, another favorite for study, provides a similar line of descent for women. In both cases since the inheritance is direct and unadulterated, it makes certain kinds of studies much easier (or even possible). The headlines from a decade ago about locating “Eve”, the earliest common mother of humankind, stemmed from studies of mitochondrial DNA.

Recently geneticists studying the Y-chromosome in Asiatic populations came upon an interesting result. Approximately 8% of the male population in large portions of Mongolia and the surrounding areas has the same Y-chromosome, indicating a shared common ancestor. The number works out to approximately sixteen million direct male descendants all sharing one common ancestor – but who is he?

Random mutations, neutral in effect, happen at a fairly consistent rate over time and they can be used much like a clock. This allowed the researchers looking across this population to work out an approximate time frame. They concluded that the lineage of this Y-chromosome converged at around 1,000 years ago – near the time of the first millennium.

The time frame eliminated the first candidate, Genghis Khan, who was born in 1162 – or did it? The researchers thought that the originating man might be a male ancestor of the Khan’s, perhaps a great-grandfather.

Certainly the hypothesis is plausible. Genghis Khan regularly sealed the conquest of new lands by taking women from their ruling families into his family. Some he married, some he gave to his relatives⁠— including his sons and brothers⁠— as wives. His eldest son, Tushi, is reported to have had forty sons of his own, and his younger sons were no different. The habit continued on for many generations, with some of his descendants holding power up until the 20th century.

Plausible or not, proving the hypothesis is another matter altogether. The only definitive proof would be to find Genghis Khan’s long hidden grave, and to recover some DNA from the Khan himself for genetic matching. In the absence of the grave, less direct support must be found.

The best evidence for the hypothesis so far, comes from outside Mongolia. In all their studies, the geneticists found only one example of this particular genetic lineage outside of the boundaries of the ancient Mongol empire. The Hazaras of Pakistan have a long oral tradition that says they are direct descendants of Genghis Khan. They also share in the lineage so commonly found in Mongolia, with almost a quarter of the Hazaras males having the Y-chromosome being tracked.

Presuming that the genetic hypothesis is correct, just how successful was Genghis Khan at propagating his lineage? After all, the world population has increased dramatically in the last thousand years, so you would expect most of the people who lived a thousand years ago to have numerous descendants. Following a strict mathematical progression, if every person who lived in the times of the Mongolian Empire had been equally successful, you would expect each man to have twenty direct male descendants. Compared to the 16 million attributed to Genghis Khan, this would make him approximately 800,000 times more successful.

Another question that arises with this data is: are there any others? So far this study is the only one of its kind. Will future studies show other historic men who have been as dramatically successful in spreading their genes? Possibly, but not necessarily. In order to achieve this kind of spread, not only does the originator of the lineage need to have a lot of male progeny, but they must be widespread geographically, and they must continue the trend for a number of generations. In Europe, there is no tradition of harems to allow for the astounding numbers of children, while in Africa, the tribal organization of a thousand years ago would make the required geographical spreading difficult. The most likely area to find another widespread lineage would be among the early Muslims. There the tradition of multiple wives had been long established, and remains today in many Middle Eastern countries, while the many trade routes, and the expansion of empires would allow for the geographical spreading.

Regardless of the results, it is interesting to see such an enormous genetic footprint still visible, the invisible legacy of a man who may just be the most successful patriarch in history.