Recent trends in fertility in less developed countries.

The rate of increase of population in less developed countries accelerated rapidly from 1850 to 1960 because of a rapid decline in mortality while fertility remained high. In the 1960's, the birth rate as a whole began to decline more rapidly than the death rate--very rapidly in some populations, most notably that of China, more gradually in others, and not at all in some of the poorest populations. The momentum of growth implies continued increase in populations for several decades even in countries where fertility has fallen the most, and very large additional increases where there has been no decline in the rate of childbearing.