Birthrate

The birth-to-death in European, American and some Asian countries is currently negative. This is a bad thing, but people either don't want to or cannot sustain properly a family any longer. The birthrate is roughly around 1.5 children per couple. This means that in about 80 years these countries would lose about a quarter of their current population. Most African countries are exceptions. Reasons for why "rich" countries have a negative birth-to-death ratio:

1. Reduction of salaries: This makes any family to become hard-to-support.
2. The invention of the condom: As unlikely as it may seem, this is a major problem. Most people don't marry any longer, since they can now engage in sexual relationships without procreating.
3. The lack of housing: Big houses are now very expensive, so there is no room for more than a couple or a small family.

Instead, in poorer countries (like African) have a huge birthrate, eventually reaching more than 4-5 children. Previously, they had a huge premature mortality rate, but new aide programms reduced it significantly. So the population in poorer countries might double soon.

The European birthrate is low.