Changes in the institution of marriage affect not only children already born. They also affect the unborn. The industrialized world, after a peak in childbearing in the late 1950s, has experienced such a sharp decline in the birthrate that the population is no longer replacing itself.
The birthrate -- measured by the number of children born per woman -- has been a matter of concern at least since 1798, when Thomas Malthus, an English economist and clergyman, published his ``Essay on the Principle of Population.'' His concern, however, was that the birthrate was too great. Predicting that overpopulation would outstrip the food supply, he raised fears that reverberated later in Paul R. Ehrlich's ``The Population Bomb'' (1968) and Donella Meadows's ``Limits of Growth'' (1972).
In the '70s, these overpopulation alarms had widespread impact. A 1970 survey found that 69 percent of married women in America agreed that US overpopulation was a ``serious problem'' -- and that many of them were lowering the number of children they intended to have.
Now, however, the birthrate in the industrial world is below the ``replacement rate'' of 2.1 children per woman. That rate is set at the number of children needed to replace every parent, with more added to account for mortality.
In 1855, white American women averaged 5.31 births -- well above the then-current replacement rate of 3.32 (higher then because of higher infant mortality). By 1980, the figure had dropped to 1.75 children each -- well below the 2.1 replacement rate. Even the high birthrate of US Hispanics -- 56 percent more than non-Hispanics in 1982 -- doesn't raise the total US rate above replacement levels.
How significant is the change? ``The nonindustrial two-thirds of the world, ill equipped to provide adequate education, is producing 92 percent of the world's next generation,'' writes American sociologist Kingsley Davis in a forthcoming book on marriage. Meanwhile, were it not for immigration, population in the industrial world would be falling at a rate of about 20 percent with each generation. He links the drop in fertility to changes in marriage.
G'erard Calot, director of the National Institute for Demographic Studies in Paris, agrees that ``the marriage crisis doesn't help the fertility situation.'' But he notes that the great changes in marriage in Europe began in 1972 -- about the time the fertility decline stabilized.
He links the drop in fertility to ``the increase in female labor-force participation'' -- and to the fact that each new child that forces a woman to stop working ``has an additional cost that is tremendous.''
But evidence from West Germany contradicts his thesis. According to Renate K"ocher of the Allensbach Institute for Public Opinion Polling, West Germany has a very low rate of labor-force participation by women. Yet it has the lowest birthrate in the world.
University of Pennsylvania sociologist Samuel H. Preston, in a paper on fertility in English-speaking countries and Japan presented at the Hoover Institution earlier this month, sees three causes for the decline in fertility: an upward-moving economy (drawing more women into the work force), improved contraception, and changes in values. Of these, he says, values are among the most influential in childbearing decisions.
Sociologist Davis observes that ``although people value children very highly, it seems likely that they will not exceed replacement-level fertility unless incentives for childbearing and child care are systematically improved and disincentives are alleviated, which in large part means reforming the institution of marriage.''