WORLD fertility trends took a significant and largely unanticipated downward turn during the decade between 1985 and 1975. Wherever it has been possible to measure fertility changes since 1970, it has been found almost without exception that birth rates have fallen, even if slightly, and in a number of eases the declines have been rather large. And these downward trends are broad-based: Several countries that are in the category “less developed” have experienced substantial declines, as have countries where the standard of living is relatively high. Moreover, the magnitude and pace of this decline is greater than many demographers had expected.