"It doesn't look like there was a massive flow of genes that came in a few thousand years ago," he said. "Clearly people came in to India and brought their culture, language, and some genes."
"But I think that the genetic impact of those people was minor," he added. "You'd don't really see an equivalent genetic replacement the way that you do with the language replacement."
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Language, Genes Tell Different Tales
Kashyap and his colleagues say their findings may explain the prevalence of Indo-European languages, such as Hindi and Bengali, in northern India and their relative absence in the south.
"The fact the Indo-European speakers are predominantly found in northern parts of the subcontinent may be because they were in direct contact with the Indo-European migrants, where they could have a stronger influence on the native populations to adopt their language and other cultural entities," Kashyap said.
He argues that even wholesale language changes can and do occur without genetic mixing of populations.
"It is generally assumed that language is more strongly correlated to genetics, as compared to social status or geography, because humans mostly do not tend to cross language boundaries while choosing marriage partners," Kashyap said.
"Although few of the earlier studies have shown that language is a good predictor of genetic affinity and that Y chromosome is more strongly correlated with linguistic boundaries, it is not always so," he added.
"Language can be acquired [and] has been in cases of 'elite dominance,' where adoption of a language can be forced but strong genetic differences remain [because of] the lack of admixture between the dominant and the weak populations."
If steppe-dwelling Central Asians did lend language and technology, but not many genes, to northern India, the region may have changed far less over the centuries than previously believed.
"I think if you could get into a time machine and visit northern India 10,000 years ago, you'd see people similar to the people there today," Underhill said. "They wouldn't be similar to people from Bangalore [in the south]."
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