Indian caste groups have differing genetic relationships to Europeans and Asians

A new study of genetic data shows that the ancestors of Indian men came from different parts of the world than those of Indian women and produced modern upper caste Indian populations that are genetically more similar to Europeans and lower caste populations that are more similar to Asians. These findings support historical data suggesting that West Eurasians migrating into India during the last 10,000 years more often left descendants in the higher rather than lower castes. The study is to be published in the June 1 edition of the journal Genome Research.

"The dispersal and subsequent growth of Indian populations during the Neolithic age is one of the most important events to have shaped the history of South Asia. Thus, it is an obvious question to ask who are the closest relatives of Indians and are the different castes more or less similar to the same relatives," says lead study author Michael Bamshad, M.D., a geneticist at the University of Utah.

Previous studies by other scientists analyzing either Y-chromosome or mitochondrial genetic data of Indian populations have often produced conflicting results, suggesting stronger similarity to either Europeans or Asians. The new study analyzed both types of data in more than 1000 people and showed that ancestors of Indian men and women came from different parts of the world. The differences likely account for the different genetic relationships shown by looking at the gender-specific Y-chromosome and mitochondrial genetic data.

Bamshad's study showed that each caste's mitochondrial DNA, which derives from the mother only, has a greater similarity to Asians than to Europeans, but the upper castes show less similarity than do the lower castes. Conversely, Y-chromosome data, derived from the father only, show each caste more similar to Europeans, with the upper castes being most similar, probably because more Eurasian males migrated to India than did Eurasian females.

To increase the power of the study, Bamshad and his co-authors also examined 40 additional genes that are inherited from the father and the mother. All of these data strongly supported the conclusion that upper castes have a higher genetic similarity to Europeans than do lower castes.

Overall, the study indicates that Indian caste populations are likely to be of Asian origin with greater West Eurasian influence on the upper castes than lower castes. These results demonstrate the power of using genetic tools to dissect human history and suggest that such complex patterns of relationship between genders and social groups may be more usual than scientists had previously thought.

Lynn Jorde, Ph.D., Professor of Human Genetics at the University of Utah, is a co-author of the study. Additional collaborators are from the Estonian Biocentre; Andhra University, India; Anthropological Survey of India; University of Madras, India; University of Arizona; University of Newcastle-upon-Tyne, United Kingdom; and the Louisiana State University Health Science Center.