Population pyramids
See here the population pyramid of Sudan (as an example). Very wide at the bottom, so lots of young people being born, very narrow at the top. This is probably what you want in each country.
Lots of young and middle aged people to pay for the fairly small older population.
http://geographyyr10....file/view/pyramid.gif
Now look at the UK. Very narrow at the bottom (few young people being born), a HUGE bulge in the middle (who are all going to get old in the next 20 years or so), and already many people in their 70s and 80s and even up to 100.
So who is going to be working (and paying) for the massive population of old people in 20 or 30 years time if you dont have children now.
This is massive problem almost all the Western countries have, which is why people will need to keep working into their 60s and even 70s.
http://www.bbc.co.uk/...y/images/pop_006a.gif