In less developed regions, life expectancy was nearly 12 years lower, at 63 years. By 2050, the less developed regions are expected to attain a life expectancy of 75 years, whereas in the more developed regions the projected level is 82 years, implying that the gap between the two groups may narrow. Only in South Africa, whose fertility is lower than that of Botswana or Zimbabwe, does the growth rate of the population become negative during 2010-2025. For the 45 most affected countries, the expectation of life at birth has already been reduced by nearly three years. In the less developed regions, the proportion of the population aged 60 or over will rise from 8 per cent in 2000 to close to 20 per cent in 2050.
International migration is projected to remain high during the twenty-first century.
The more developed regions are expected to remain net receivers of international migrants, with an average gain of about 2 million per year over the next 50 years. Because of low fertility, this migration has a significant impact on population growth in the more developed regions. Without migration, the population of more developed regions as a whole would start declining in2003 rather than in 2025, and by 2050 it would be 126 million less than the 1.18 billion projected under the assumption of continued migration. The full results of the 2000 Revision will be issued in a series of three volumes that are under preparation. For most populations, replacement is ensured with a fertility of 2.1 children per woman.