The famous TV commercial of our beloved Jr. Bachchan explaining the reason for more than a billion human souls in our homeland first felt like a banal comic act to just continue the "Bhat an Idea" campaign. Not until a supposedly very intelligent/or just intelligent friend of mine seriously quoted the reason in one conversation. And also his flatmate there. And then they quoted it a second time. I had to shed my lethargy and blurted "U really believe in what they are saying"? And their expression was like huh, have u even got a brain there? Dont you know India has always been a backward (always?) nation. Ok wouldnt even argue on that one. So? What about the Europeans? Did they have the trendy phones with a xG connectivity ever since the land was carved out? After a few minutes of senseless arguments, atleast the question came "Ok so what do you think would be the reason of our mammoth population? Wars, I reckon. The Europeans lost entire generations of men in the wars they have fought among each other as tribes for ages. Their tribal footing in any case started pretty late - the Frank (modern day French) and Germanic (Germany etc) tribes et al were forest dwellers as late as the 4th century into the first millenia after the christ trudged. India on the contrary has been there since much before (even if we discount the mythology, the Buddha and Mauryas wrote indelible history 500 years before the christ. What is however more important is that Indians have never really fought wars or witnesses large scale demolotion of the populace. The foreign rulers established their holds among the people since at least the last thousand years without any significant bloodshed in retaliation really. Even the movement for Independence was wrought with nonviolence. So all things equal India would anyway grow much fast. But even the other things have not been equal historically. The black death - the dreaded plague - of the 14th century wiped half of the European continent. The world wars have been the most recent among the annihilation sagas. I might have made - terribly tired that I am - an error here and then there at this time of the night, but I do not find it not to be a better explanation of India's high population. What about China you might ask. I would put forth my reasons later. Size and strength are two pointers I would just throw for now.
