I read an article once that showed how breeding patterns change in humans. Essentially, humans in third-world countries breed lots, as mortality rates are so high. Those in first world countries barely breed enough to replace the population. But, as a country moves from third to first world, breeding stays high (as that is what they are culturally used to), but mortality rates drop. This gradually changes to first-world breeding patterns over a couple of generations. The problem is this: in the transition period, the population of the country explodes. Usually, this is problematic for the country involved, but not to the greater planet. The problem now is that two of the biggest countries in the world - India and China - are just starting the transition process. China is at least trying to stem the problem early, but India's population could rise very quickly over the next 40-50 years.