About 5,000 years ago, people from west Eurasia are thought to have first entered India. Once there, they presumably mixed with the native proto-Asian population living on the subcontinent. But historians credit these same Indo-Europeans with creating the current Hindu castes, and it seems that in doing so, they placed themselves at the top of this class system, perhaps one they superimposed on an existing social order. Because marriages between members of different castes have traditionally been taboo in India, the newcomers would have very likely intermarried only with native Indians of higher standing.

To test this theory, an international team of researchers from India, Europe and the U.S. compared maternally inherited DNA variationsas well as paternally and bi-parentally inherited variationsof 265 Indian men from eight different castes with those of 750 African, European, Asian and other Indian men. Their findings, published in this month's issue of Genome Research, were two-foldand largely confirmed the idea that members of higher castes are more closely related to Europeans.

The researchers discovered that the maternally inherited DNA more closely resembled that of Asians, although genetic similarities to Europeans were more common in members of the higher ranks. Among the paternally inherited DNA, however, they found an even greater likeness to European DNA. Thus, the scientists suggest that the western Eurasians who arrived in India were mostly men who placed themselves at the top of the social ladder and married only women in the highest castes.