The caste system in South Asia — which rigidly separates people into high, middle and lower classes — may have been firmly entrenched by about 2,000 years ago, a new genetic analysis suggests. Researchers found that people from different genetic populations in India began mixing about 4,200 years ago, but the mingling stopped around 1,900 years ago, according to the analysis published today (Aug. 8) in the American Journal of Human Genetics. Combining this new genetic information with ancient texts, the results suggest that class distinctions emerged 3,000 to 3,500 years ago, and caste divisions became strict roughly two millennia ago. Though relationships between people of different social groups was once common, there was a "transformation where most groups now practice endogamy," or marry within their group, said study co-author Priya Moorjani, a geneticist at Harvard University. Ancestral populations Hindus in India have historically been born into one of four major...