Five thousand years ago, the ancestors of modern Indians were comprised primarily of two groups: ancestral North Indians, who related to people of Central Asia, the Middle East, the Caucasus, and Europe, and ancestral South Indians, who are not closely related to groups outside the subcontinent. The mixture between these two groups and their many subcategories happened mostly between 4,200 and 1,900 years ago, according to the study. The authors note that this period is significant as it was a "time of profound change in India, characterized by the deurbanization of the Indus civilization, increasing population density in the central and downstream portions of the Gangetic system, shifts in burial practices, and the likely first appearance of Indo-European languages and Vedic religion in the subcontinent.” 

Around 1,900 years ago, the mixture largely stopped, as Indian society moved toward endogamy—the practice of avoiding intermarriage or close relationships between ethnic groups—which reached its most extreme form in the creation of the caste system. As one of the study’s authors told the Times of India, "the present-day structure of the caste system came into being only relatively recently in Indian history."

1900 years ago is just after the Jewish Diaspora.

I have often wondered why there are Jews in every part of the world except India.

I guess this non-intermarriage credo was also true for non-Indians, too.

So the Jews who went in that direction continued east.