Arun's recent post on the subject of Indian origins piqued my interest in the subject. There are a few oddities about the population of India, including evidences of ancient occupation of the place by peoples very similar to the present inhabitants and a wide variety of physical types. In addition. a dominant language, closely associated with Indian elites for millenia, is closely related to a large group of European languages and appears to be descended from a common ancestor.
The conventional interpretation has been that the Indo-Europeans, perhaps the first masters of horses as weapons of war, conquered many territories, including India, and left the local populations with their language, elements of their culture, and some of their genes. The study cited by Arun appears to challenge this. Such views are popular in India, probably in part due to nationalistic feelings and reluctance to concede local cultural autonomy.
A more recent study is more friendly to the conventional theory. It found that while the Indian population is overwhelmingly dominated by old Asian genes, there is (1) a significant admixture of European genes and (2) the European gene content varies among castes and increases with increasing caste status (3)there are differences between what the mtDNA (maternal line) and Y chromosome (paternal line) data show.
Genetic distances estimated from Y-chromosome STR polymorphisms differ significantly from zero (p < 0.001) and reveal a distinctly different pattern of population relationships (Table3). In contrast to the mtDNA distances, the Y-chromosome STR data do not demonstrate a closer affinity to Asians for each caste group... ...
For Y-chromosome biallelic polymorphism data, each caste group is more similar to Europeans (Table4), and as one moves from lower to middle to higher castes the genetic distance to Europeans diminishes progressively. This pattern is further accentuated by separating the European population into Northern, Southern, and Eastern Europeans; each caste group is most closely related to Eastern Europeans. Moreover, the genetic distance between upper castes and Eastern Europeans is approximately half the distance between Eastern Europeans and middle or lower castes. These results suggest that Indian Y chromosomes, particularly upper caste Y chromosomes, are more similar to European than to Asian Y chromosomes. This underscores the close affinities between Hindu Indian and Indo-European Y chromosomes based on a previously reported analysis of three Y-chromosome polymorphisms (Quintana-Murci et al. 1999b).
This study supports the idea of an admixture of European genes into what either already were or subsequently became the upper castes, and that the European genes were mainly from the European males.
It seems safe to say that as genetic analysis proceeds evidence for one theory or the other will become overwhelming. It also seems likely that politics and science will continue to be uneasy bedfellows.