India is enjoying an extended economic boom, with near double-digit growth. But the benefits have not been equally shared, and southern India has rocketed far ahead of much of the rest of the country on virtually every score — people here earn more money, are better educated, live longer lives and have fewer children.

A crucial factor is the collapse of the caste system over the last half century, a factor that undergirds many of the other reasons that the south has prospered — more stable governments, better infrastructure and a geographic position that gives it closer connections to the global economy.

“The breakdown of caste hierarchy has broken the traditional links between caste and profession, and released enormous entrepreneurial energies in the south,” said Ashutosh Varshney, a professor at Brown University who has studied the role of caste in southern India’s development. This breakdown, he said, goes a long way to explaining “why the south has taken such a lead over the north in the last three decades.”

India’s Constitution abolished discrimination on the basis of caste, the social hierarchy that has ordered Indian life for millenniums, and instituted a system of quotas to help those at the bottom rise up. But caste divisions persist nonetheless, with upper castes dominating many spheres of life despite their relatively small numbers.

While in the south lower caste members concentrated on economic development and education as a route to prosperity, in the north the chief aim of caste-based groups has been political power and its spoils. As a result India’s northern lower castes tend to be less educated and less prosperous than their southern counterparts. Charismatic leaders in the north from lower castes have used caste identity as a way to mobilize voters, winning control over several large north Indian states. Caste so thoroughly permeates politics in the northern half of the world’s largest democracy that it is often said that people don’t cast their vote; they vote their caste.