Some notes from a trip to the CIA World Factbook.
Comparing the growth rates of India and China, it seems that within 5 years India will surpass China to become the world's most populous country.
Also, a look at fertility rates shows that world population growth is concentrated in Africa and the Indian subcontinent. The rest of the world has, or can expect, a low rate of population growth (a few small countries are exceptions though).
And Iran has the world's lowest fertility rate (births per mother) except for Europe, four East Asian countries, and several small island countries. Perhaps indicating that despite (or because of) the fundamentalist government policies, the population has become quite secular.