India cultivated homegrown farmers.

Approximately 10,000 years ago, hunter-gatherers living in what's now India adapted agricultural practices for their own purposes rather than giving way to an influx of foreign farmers, a new genetic study suggests.

Comparisons of men's Y chromosomes show that nearly all Indian men today, regardless of their tribe or caste, are descendants of populations that inhabited South Asia before agriculture's introduction to the region, concludes a team led by Vijendra K. Kashyap of the National Institute of Biologicals in Noida, India.

The scientists analyzed Y chromosome differences among 936 Indian men representing 77 different populations, including castes. Participants spoke languages from the country's four major linguistic groups.

Indian men from the various groups displayed substantial genetic similarities and few signs of DNA influences from western Asia, where other researchers had already probed patterns in male chromosomes. A gradually declining frequency of common Y chromosome markers from southern to northern India and into central Asia indicates that India's ancient inhabitants migrated northward, Kashyap's team concludes in an upcoming Proceedings of the National Academy of Sciences.

Because modern caste populations in India often cultivate crops and speak Indo-European languages, researchers have long hypothesized that these people derived from western or central Asian farmers who migrated southward. Native South Asians more likely borrowed agriculture techniques and developed them on their own, assert Kashyap and his coworkers.

Previous studies of mitochondrial DNA, which is inherited through the mother, suggest that Africans settled South Asia between 70,000 and 40,000 years ago.

A related debate concerns whether agriculture spread throughout Europe as a result of the migration of Middle Eastern farmers or of the adoption of cultivation by native Europeans (SN: 12/3/05, p. 358).--B. B.