Y chromosomes trace dominance of Manchu dynasty20 Oct 2005
A study by Yali Xue and colleagues in the advance section of American Journal of Human Genetics
Here's the abstract:
We have identified a Y-chromosomal lineage that is unusually frequent in northeastern China and Mongolia, in which a haplotype cluster defined by 15 Y short tandem repeats was carried by 3.3% of the males sampled from East Asia. The most recent common ancestor of this lineage lived 590 340 years ago (mean SD), and it was detected in Mongolians and six Chinese minority populations. We suggest that the lineage was spread by Qing Dynasty (16441912) nobility, who were a privileged elite sharing patrilineal descent from Giocangga (died 1582), the grandfather of Manchu leader Nurhaci, and whose documented members formed 0.4% of the minority population by the end of the dynasty.
While introducing the problem, the paper presents a couple of stumbling blocks that the study had to overcome. The Y chromosome is relatively less variable than much of the rest of the genome, but viewed at an appropriate level of detail (i.e. with a fairly large number of microsatellite sites), geneticists can reach a level of variation at which most individuals are completely unique. If you look at 15 or so microsatellites, it is fairly unlikely that two people in a moderately large sample should have the same Y chromosome haplotype, unless they happen to be close relatives.
But there are lots of reasons why close relatives might actually end up in a moderately large sample. For one thing, the sample usually comes from a small number of locations, which means that some alleles may have relatively high frequency in the sample because of their predominance at a single location. This happens when distant cousins (perhaps unbeknownst to each other) get in the sample. In small villages and towns, this becomes more likely because of inbreeding.
On the other hand, alleles that are common and occur in many locations are truly unusual. These alleles must not only represent the history of a small village or town, but must represent a more widespread pattern of ancestry across large regions. Alleles ultimately come from people, and Y chromosome haplotypes ultimately come from a single man.
As discussed by Xue et al. (2005), there are at least two such unusually common alleles in East Asian populations. These are instances in which the descendants of one man had unusually great success in passing their Y chromosomes to many descendants, across broad geographic areas. Sons, grandsons, and further descendants spread out and maintained much higher rates of reproduction (at least, of sons) than other men who lacked the peculiar widespread Y haplotype.
One of these haplotypes was described by Zerjal et al. (2003), in their paper "The Genetic Legacy of the Mongols".
In case you missed that paper, here is its abstract, which pretty much says it all:
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. The pattern of variation within the lineage suggested that it originated in Mongolia 1,000 years ago. Such a rapid spread cannot have occurred by chance; it must have been a result of selection. The lineage is carried by likely male-line descendants of Genghis Khan, and we therefore propose that it has spread by a novel form of social selection resulting from their behavior.
The logic leading to this conclusion is indirect, depending on the high frequency and widespread distribution of the haplotype, the general match between the geographic range of the haplotype and the range of Mongol conquests, the historical record of descent of local kings and rulers from Mongol antecedents, and the likelihood that only members of a high-ranking elite would have had the opportunity to maintain high reproduction for many generations across the entire area.
The other widespread recent haplotype is described in detail by Xue and colleagues (2005). Its association to historic events is also indirect, but likewise plausible:
We reasoned that the events leading to the spread of this lineage might have been recorded in the historical record, as well as in the genetic record. The spread must have occurred after the cluster's TMRCA (500 years ago, corresponding to about A.D. 1500) and, most likely, before the Xibe migration in 1764. Notable features are the occurrence of the lineage in seven different populations but its apparent absence from the most populous Chinese ethnic group, the Han. A major historical event took place in this part of the world during this period - namely, the Manchu conquest of China and the establishment of the Qing dynasty, which ruled China from 1644 to 1912. This dynasty was founded by Nurhaci (1559-1626) and was dominated by the Qing imperial nobility, a hereditary class consisting of male-line descendants of Nurhaci's paternal grandfather, Giocangga (died 1582), with >80,000 official members by the end of the dynasty (Elliott 2001). The nobility were highly privileged; for example, a ninth-rank noble annually received 11 kg of silver and 22,000 liters of rice and maintained many concubines. A central part of the Qing social system was the army, the Eight Banners, which was made up of separate Manchu, Mongolian, and Chinese (Han) Eight Banners. The nobility occupied high ranks in the Manchu Eight Banners but not in the Mongolian or Chinese Eight Banners; the Manchu Eight Banners were recruited from the Manchu, Mongolian, Daur, Oroqen, Ewenki, Xibe, and a few other populations. A social mechanism was thus established that would have led to the increase of the specific Y lineage carried by Giocangga and Nurhaci and to its spread into a limited number of populations. We suggest that this lineage was the Manchu lineage (Xue et al. 2005:3-4).
The thing that interests me is the extent to which the hypothesis can be judged only on its historic merits. The date of the founding of the haplotype is very imprecisely known. The paper lists two contrary estimates of around 590 and around 220 years ago, based on different estimates of microsatellite mutation rates, and each having substantial error. If we just take the total range of the standard error of both estimates, which must be less than the confidence intervals, this is a range of anywhere from 1070 AD to 1900 AD for the origin of the haplotype.
So the historical association of the haplotype really depends on historical evidence. It is all plausible, but it serves as a bit of a reality check on genetics. Here we have a good indication from genetics of the scale of the phenomenon -- this one patriline has come to represent a very high proportion of the living people of East Asia. From history alone, we might not have guessed the sheer magnitude of reproductive dominance of the Chinese ruling elite. Here, genetics makes a very important contribution.
But whether this patriline was Manchu or some earlier ruling elite, or whether it was a ruling elite at all instead of some extraordinarily active farmer -- those details depend on a full rendering of the relevant history. Genetics gives only a bare skeleton of the timing and place of the founding of the patriline and its later dispersal. History can focus on one hypothesis because it can rule out alternatives -- perhaps only the Manchu ultimately had the right distribution and access at the right time to explain the pattern of genetic data.
I don't think the matter is decided yet. Again, I think the association is perfectly plausible. But historians need to wake up and address these kinds of genetic inquiries with their evidence. At the moment, we have suspects and circumstantial evidence.
The geneticists would like to add more:
Our hypothesis could be tested by examining the descendants of the Qing nobility (Li 1997). Unfortunately, extensive warfare during the 20th century and the Cultural Revolution (1966-1976) led to enormous social upheaval, during which descent from the nobility was usually hidden and relevant documents were destroyed. As a result, very few well-attested descendants are known, and they were not available for testing. Thus, our hypothetical explanation remains unproven (Xue et al. 2005:4).
Up to now, genetics has remained a consumer of historical evidence. It is on a course to become a major producer as well. I'd like to read the historian who is ready to adapt to this new source of information.
Xue Y, Zerjal T, Bao W, Zhu S, Lim S-K, Shu Q, Xu J, Du R, Fu S, Li P, Yang H, Tyler-Smith C. 2005. Recent spread of a Y-chromosomal lineages in northern China and Mongolia. Am J. Hum Genet 77 (early access). Full text (free)
Zerjal T, Xue Y, Bertorelle G, Wells RS, Bao W, Zhu S, Qamar R, Ayub Q, Mohyuddin A, Fu S, Li P, Yuldasheva N, Ruzibakiev R, Xu J, Shu Q, Du R, Yang H, Hurles ME, Robinson E, Gerelsaikhan T, Dashnyam B, Mehdi SQ, Tyler-Smith C (2003) The genetic legacy of the Mongols. Am J Hum Genet 72:717-721. Full text