A Prolific Genghis Khan, It Seems, Helped People the World - New York Times
A Prolific Genghis Khan, It Seems, Helped People the World
A remarkable living legacy of the Mongol empire has been discovered by geneticists in a survey of human populations from the Caucasus to China.
They find that as many as 8 percent of the men dwelling in the confines of the former Mongol empire bear Y chromosomes that seem characteristic of the Mongol ruling house.
If so, some 16 million men, or half a percent of the world's male population, can probably claim descent from Genghis Khan.
The finding seems to be the first proof, on a genetic level, of the occurrence in humans of sexual selection, a form of sex-based natural selection in which a male or female has an unusual number of offspring. This process can greatly influence the genetic makeup of a species, resulting in otherwise puzzling features like the peacock's cumbersome tail.
The survey was conducted by Dr. Chris Tyler-Smith of Oxford University and geneticist colleagues in China, Pakistan, Uzbekistan and Mongolia. Over 10 years they collected blood from 16 populations that live in and around the former Mongol empire.
In the late 13th century the sons of Genghis Khan controlled territory that stretched from the Pacific coast of China to the Caspian Sea, spanning land now held by the Central Asian republics and the northeast corner of Iran.
Dr. Tyler-Smith's team analyzed the DNA of the Y chromosome, a part of the genome that is useful for establishing human lineages because, like a surname, it is passed down from father to son.
They found that a cluster of Y chromosomes carried a genetic signature showing they were closely related to one another and to a single founder chromosome in the recent past. These signature chromosomes were far more common than would be expected by chance among most of the populations living within the former Mongol empire. But none of the peoples outside the empire carried the chromosomes, except for the Hazara people of Pakistan and Afghanistan, former Mongol soldiers who claim descent from Genghis Khan.
Dr. Tyler-Smith said the signature chromosomes probably belonged to members of the Mongol ruling house. They could have become so common in part because of the rapes that occurred during the Mongol conquest, but more probably because the Mongol khans had access to large numbers of women in the captive territories they ruled for two centuries. An article about the geneticists' findings has been published electronically by The American Journal of Human Genetics.
Genghis Khan's sons and heirs ruled over the various khanates in his empire, and may well have used their position to establish large harems, especially if they followed their father's example. David Morgan, a historian of Mongol history at the University of Wisconsin, said Genghis's eldest son, Tushi, had 40 sons.
As for Genghis himself, Dr. Morgan cited a passage from 'Ata-Malik Juvaini, a Persian historian who wrote a long treatise on the Mongols in 1260.
Juvaini said: ''Of the issue of the race and lineage of Chingiz Khan, there are now living in the comfort of wealth and affluence more than 20,000. More than this I will not say . . . lest the readers of this history should accuse the writer of exaggeration and hyperbole and ask how from the loins of one man there could spring in so short a time so great a progeny.''
Dr. Morgan said that since Mongol rulers controlled a large area, it was ''perfectly plausible'' that they should have fathered many children. ''It's pretty clear what they were doing when they were not fighting,'' he said.
The Mongol rulers' apparent assiduity in propagating their genes has surprised even human behavioral ecologists, researchers who seek to explain many aspects of human society in terms of the pursuit of reproductive advantage.
''I think it's astonishing,'' said Dr. Robin Dunbar of the University of Liverpool, co-author of a leading textbook of human behavioral ecology. ''This is a staggering example of how a very small lineage can have a hugely disproportionate share of the descendant population.''
Dr. Dunbar said it was known that in tribes like the Yanomamo of Brazil, men of high status tended to have more children. But the Mongol study was the first to his knowledge to document this on a genetic level. ''It's exactly equivalent to elephant seals slogging it out on the beach -- a handful of males get all the matings,'' he said.
The practice may have been common in human history and would explain why so many male lineages have gone extinct, leaving a single survivor. It could also explain why ''Adam,'' the common ancestor of all Y chromosomes, seems to have lived much earlier than ''Eve,'' the common ancestor of all mitochondria, genetic elements passed down through the female line, Dr. Dunbar said. When some individuals have far more children than others, the formula for calculating the time to the common ancestor yields a much earlier date.
Dr. Tyler-Smith and his colleagues estimate that the common ancestor of the signature chromosomes they found in the Mongol empire populations lived in around A.D. 1000, 162 years before the birth of Genghis Khan. Dr. Morgan said, ''I see no reason why the family shouldn't have descended in a straight line'' from that time to Genghis Khan.
The geneticists' evidence for linking the cluster of signature chromosomes to Genghis Khan is necessarily indirect. The Mongol ruler was buried secretly and his tomb has not been found, let alone any bodily remains that might still harbor fragments of DNA. But the signature chromosomes are carried by only a fifth of present-day Mongolian men, suggesting they belonged to an elite group, presumably the lineage of Genghis Khan and his sons.
Dr. Tyler-Smith and his colleagues argue they have found a second link to Genghis Khan, through the Hazaras, whose oral tradition holds that some of them are his direct descendants. The fact that the Hazaras carry the signature chromosome confirms their oral tradition of descent from Genghis and suggests he carried the chromosome too, the geneticists say.
But historians find fault with this argument. Dr. Morris Rossabi, a Mongol expert at Columbia University, described the Hazaras' claim to be direct descendants of Genghis Khan as ''untenable.''
''They are descendants of troops and guards sent by Chinggis to this region, and I would be very suspicious about a genealogy based on their so-called oral traditions,'' Dr. Rossabi wrote in an e-mail message. (Chinggis is a more correct spelling of the familiar Genghis.)
The name Hazara, from the Persian word for ''thousand,'' suggests a Mongol military formation and the Hazaras do look Mongol, Dr. Morgan said, although unlike some villagers in Afghanistan who still speak archaic Mongol, the Hazaras themselves speak Dari, a form of Persian. Some Hazaras may have been Mongol soldiers but none of the imperial house ruled in Afghanistan, Dr. Morgan said, making it hard to argue that the Hazaras' signature chromosome comes directly from Genghis.
Asked if the Mongol rulers' vigorous propagation of their genes was default human behavior, given the opportunity, Dr. Dunbar laughed and said it was probably an extreme form, and not universal. But it illustrated the keen interest some men have in using their power and status to maximize their reproductive advantages, he said.
