Prabhat
I think Chetan’s answer (Original Archives) is the best one: How the Indian subcontinent was peopled is a matter of considerable uncertainty and controversy. I feel compelled, however, to add that some of the earlier answers are almost certainly wrong.
There are two points: 1) I don’t think any paleontologist believes that human beings existed on the planet at a time when India and Africa could have been physically joined. Indeed, what I consider the most compelling contemporary theory of human origins suggests that human beings didn’t even begin to leave Africa until about 100,000 years ago – a mere moment in geologic time scales. To be blunt, it is inconceivable that humans just walked directly from Africa to India.
2) While the idea of an Aryan invasion of India around 1500 BCE was at one time a popular explanation of India’s ethnic makeup, in more recent decades large sections of the theory have been completely discredited. This is too complicated a question to be addressed here, but an important point to make is that most scholars nowadays downplay the idea that there was a sharp “racial” difference between the original speakers of Indo-Aryan languages and those of Dravidian languages.
I’ll also simply mention that the “African” features of some southern Indians probably say more about their kinship with the aboriginal peoples of Australia than they do about their connections to Africa.
Again, as Chetan said, this is a convoluted (but fascinating) subject that would be best satisfied by a visit to the library.