Stone-age innovation explains ancient population boom - life - 21 July 2009 - New Scientist: "Petraglia and his colleagues contend that the beginnings of a global ice age pushed ancient populations of Indians into closer contact – and competition – with one another. 'They need to develop new strategies to produce new resources. They invent microlithic technology and it spreads very rapidly.'"
Something as simple as a good and easy to manufacture stone knife may have allowed India to support the population it now has.
Oh, and it was because of global cooling. lol.