With its dozens of languages and profound differences in architecture, music, and diet, the world's second largest nation is fascinatingly heterogeneous.
One of the more improbable themes within this vast symphony of difference is the Jewish one. Groups claiming Jewish ancestry are dotted across the subcontinent. And now two British scholars using the latest DNA testing techniques have come to India to determine what genetic substance there might be to their beliefs.
Tudor Parfitt is a scholar of Jewish history at the School of Oriental and African Studies in London; Neil Bradman is a Jewish publisher who has made a second career, building on a postgraduate degree in biology, as a geneticist.
Outside a dilapidated synagogue in the town of Alibag, south of Bombay, spiritual home of what is claimed to be India's oldest Jewish community, they go about their work. Each volunteer is helped to fill out a questionnaire; Mr Parfitt snaps them with a Polaroid camera (the free snap is what induces them to take part). And Mr Bradman runs a swab around the mouth of each and puts the sample in a test tube.
The Bene Israel, or Sons of Israel, were first identified as Jews at the end of the 18th century by a co-religionist from the large Jewish community in Cochin, Kerala.
The Bene Israel believe that their ancestors were Jewish traders, shipwrecked on these shores 2,000 years ago. During their long sojourn in India they had lost most of their religious practices, but the Jew from Cochin was alerted to the truth by their notion of what was and was not kosher.
They had another Jewish custom, the hanging of mezuzahs, or encased prayer scrolls, on their doorposts for good luck. Many of the Bene Israel have now emigrated to Israel, but the mezuzah custom has been adopted by many in the majority Hindu community. Mr Parfitt and Mr Bradman are testing to discover to what extent the Jewish genetic legacy has been passed on, too.
Mr Parfitt and Mr Bradman are trying to gain a deeper understanding of population movements. Jews are a suitable case for study because they have a paternally inherited priesthood, the Cohanim, which means that the Y-chromosome, the long strand of DNA which contains the genetic formula for maleness, is passed from father to son practically unchanged for thousands of years. The existence of identical Y-chromosomes in groups hundreds or thousands of miles apart provides unshakeable proof of population movements.
The British pair are also interested in the Kukis, a tribe settled in the remote north-eastern state of Manipur. They call themselves Bene Manaseh, "the sons of Manaseh". Originally converted to Baptism, after the Second World War a prophet arose among them declaring that before they were Christians they were "something else" - namely, Jews.
It may turn out that, genetically, there is nothing in it. Indian bureaucracy has barred the pair from visiting the area. They will be back, however, with the tools that could yet prove that the Kukis' prophet got it right.