In the Times Literary Supplement, John Tyler Bonner, a biology professor at Princeton, described the fundamental changes he had lived through in his long professional career. In the early decades of this century, evolutionary biologists took over the model that Charles Darwin had bequeathed to them, and subsequently the field of population genetics continued with the same object of analysis, species in the mass. Many of the dramatic breakthroughs, however, came from research concentrated on the single individual or even the single gene.
Similarly, one can say that Robert Malthus gave demographers, who were organizing their discipline during the same several decades, the framework of their analyses. So long as their principal emphasis was on mortality, broad-scale statistical studies worked very well, for motivation could be largely ignored. Shifting the same type of calculation to fertility, however, incurred problems, which became apparent only after a considerable time and which have not yet been resolved. For the past century there has been a war between prospective parents and state bureaucracies over who shall decide on the size of families. First in Europe, then in the Third World, fierce battles have been fought, and the state won rather few of them.
Like all other species, humans are profligate in the supply of their reproductive matter. Males produce millions of spermatazoa, only one of which can fertilize each receptive egg. At the start of her fecund years, each female has some 200,000 to 400,000 oocytes, as immature ova are called. Most of these potential eggs, however, decompose at an early stage, and during her reproductive life perhaps as few as 400 will be ovulated, and of the fertilized ova perhaps only one in five will implant itself in the wall of the uterus, the first step to the formation of a fetus. The number of potential offspring from a single mother, thus, provides a very wide margin for the frequent mishaps.
Given this physiological framework, what is the maximum number of children that a population can produce? The largest recorded families have been in an Anabaptist sect called Hutterites, after their sixteenth-century founder, Jakob Hutter. From their original home in Moravia, they moved to Russia and then, in the late nineteenth century, to South Dakota, with eventual daughter colonies elsewhere in the United States and Canada. With an average of more than ten children in every completed family, Hutterites have been taken as the measure of "man's capacity to reproduce," the title of a pioneering work on their reproductive system. Though conversions have been few (fewer even than the tiny number of defections), their population in the United States rose from 443 persons in 1880 to more than fifty times that number in a bit more than a century.
Ansley Coale, an economics professor at Princeton, devised an elegant measure of family size based on this anomalous population. If a woman marries at age fifteen and, throughout her fecund period, has the same number of children that Hutterites do in each age interval, she will bear an average of 12.6 children during her lifetime. If we take this to be a population's maximum potential (individual families have, of course, been larger), the reproduction of less prolific peoples can be related to this base by what Coale termed the index of overall fertility.
What is it, then, that cuts down the actual family size below this potential in virtually all societies? Everywhere the typical age at marriage fluctuates about a figure set by more or less stable cultural imperatives. In what the British statistician John Hajnal called the "European pattern" of family formation, its distinctive features have been an advanced age at marriage and a large proportion of adults who remain single. With the poor quality of relevant statistical data, etymology provides the best evidence of how early this pattern evolved. The word husband derives from two words meaning house and dwell, and its original meaning (still visible in husbandman and husbandry) was a man who owned a home. In Middle English (roughly, 1150 to 1400), the word for an unmarried man was anilepiman. These two terms, one referring to the management of property and the other to marital status, gradually became associated as opposites,: with anilepiman coming to mean a man who had no living and therefore could not marry, and husband, a man who was able to care for a family and therefore could get (or, eventually, was) married.
Seemingly, the standard that a marriage should be founded on the ability to care for the resultant family is contradicted by the usual inverse relation between-social class and fertility: in the modern West those better able materially to care for children have generally had fewer of them. To understand this relation, one must place it in the context of upward mobility. One of the best studies of the matter is a book titled Prosperity and Parenthood (1954) by the English sociologist J. A. Banks. During the nineteenth century, when Britain became the world's wealthiest nation, it was possible for many to climb into high social strata. To succeed, aspirants had to set and maintain an appropriate style of life, with a minimum of one full-time servant, a carriage, and an annual holiday away from home. Outlays for children, especially the cost of the socially requisite boarding school, rose steadily, and reducing family expenditures was accomplished mainly by postponing the formation of families. Among the clergymen, doctors, lawyers, aristocrats, merchants, bankers, manufacturers, and other Englishmen of the gentleman class who married between 1840 and 1870, the average age was a shade under thirty years. Not only in Britain but also in other Western countries, the decline in fertility began in the rising middle class and from there gradually spread to the rest of society.
Banks's study suggests that reproduction must be perceived not merely as "natural," with all that that...