Birth rates are falling but the number of men and women likely to have
children keeps on growing. The United Nations Population Division (UNPD) 2008
Revision medium projection of 9.15 billion population in 2050 was 100 million
lower than in its 2006 Revision, but 200 million higher than the 2002 Revision.
One reason is population momentum - the effects of high birth rates decades
ago mean that there are now twice as many fertile women worldwide today
than there were in 1970. A halving of birth rates can be cancelled out by an
increase in the number of potential mothers.