Fertility Determinants

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There have been two periods of intense interest in the determinants of fertility by demographers. The first period, which encompasses the late nineteenth and early twentieth centuries, was dominated by a concern about differential fertility within Western countries; in this period, leaders of the eugenics movement enlisted the services of demographers to learn how these differentials could be reduced, either by increasing the fertility of some groups or lowering the fertility of others. The second period, encompassing the 1940s to the late 1980s, was dominated by concern about differences in fertility (and thus in population growth rates) between Western countries and those countries known variously as, "less developed," "developing," "Third World," and, most recently, "Southern." In this period, there was little effort to raise fertility in low-fertility societies but a great deal of effort by an international population movement composed of neo-Malthusians and family planners to lower fertility in high-fertility societies by promoting the use of modern contraception. Again, policy makers turned to demographers to learn about the determinants of fertility. At the end of the twentieth century, fertility appears to have a lower place on the agenda of demographers. In some Western countries where national population growth rates are below replacement, there is increasing concern about fertility that is considered to be too low; groups that have fertility considered to be too high are largely adolescents and, in some countries, immigrants. Many Southern countries and some Western policy makers, however, remain concerned about levels of fertility, particularly in poor countries where fertility declines are just beginning. I begin by describing fertility determinants in pretransition societies (those characterized by an absence of deliberate attempts to limit family size) and then describe fertility transitions in Europe and the Third World.


Fertility refers to the actual childbearing performance of individuals, couples, groups, or populations. Fertility transitions are best defined not in terms of a change in level (from high to low) but rather in terms of reproductive practices. Pretransition societies are those in which married couples do not effectively stop childbearing once they reach the number of children they desire; correspondingly, the onset of a fertility transition is marked by the adoption of practices to stop childbearing before the woman's physiological capacity to reproduce is exhausted. More precisely, in pretransition societies behavior is not parityspecific; that is, it does not depend on the number of children the couple has already borne (Henry 1961). At some point in time, presumably all societies were pretransition; currently, there are few societies where fertility remains high (most are in sub-Saharan Africa) and even fewer where there are no signs that a fertility transition may have begun (Bongaarts and Watkins 1996).


Despite the absence of parity-specific control in pretransition societies, fertility varies across individuals, couples, and groups: Observed total fertility rates for a population are as high as twelve (married Hutterites in the 1920s) and as low as four to five (the Kung hunters and gatherers in the 1970s and rural Chinese farmers around 1930). Important advances in understanding the sources of this variation followed a distinction between the "proximate" determinants of fertility and the "true" determinants of fertility, a distinction that owed much to an earlier systematic classification of influences on fertility made by Kingsley Davis and Judith Blake (1956). The proximate determinants are direct determinants of fertility, the combination of biological and behavioral channels through which the "true" determinants—the social, economic, psychological, and environmental factors—affect fertility (Bongaarts 1978).

In pretransition societies, the two most important of the proximate determinants of the overall level of fertility are marriage patterns and breastfeeding patterns. The other proximate determinants—fecundability (the monthly probability of conceiving among women who menstruate regularly but do not practice contraception), the use of contraception, the risk of spontaneous intrauterine mortality, and induced abortion—play a lesser role in accounting for variations in fertility (Bongaarts and Menken 1983). Marriage patterns are important, since in most societies childbearing occurs within marriage. Thus, the proportion of women who are currently married at the ages at which reproduction is physiologically possible has a major influence on fertility. There is a striking difference between the marriage patterns of Western Europe and countries of European settlement, such as the United States, Australia, and New Zealand, and societies in other parts of the world, particularly Asia and Africa. In the former, marriage has been relatively late at least since the fourteenth century, and substantial proportions of women remain lifelong spinsters. In Africa and Asia, the typical pattern has been that marriage for women is early (usually as soon as a woman is able to bear a child she marries), and virtually all women marry. Obviously, the reproductive span in Western countries has been on average shorter than that in Asian and African societies. The peculiar Western European marriage pattern is associated with a nuclear family household ideal. In Western countries, couples typically set up their own households after marriage; in Asia and Africa, in contrast, the ideal has usually been that sons bring wives into their parents' household, while daughters go to live in the parental households of their husbands (Laslett 1972). Since the ability to support one's own household is associated with age, it is not surprising that the age of marriage has been later in Western countries than elsewhere.

Within marriage, the major determinants of variations in fertility across groups in populations in which little or no contraception is practiced is breast-feeding, since nursing inhibits the return of ovulation. In addition, in some societies a period of abstinence from sexual intercourse is prescribed by local custom, often because it is believed that intercourse during this period will harm the mother or the child. Post-partum abstinence taboos have been found to vary from a few weeks to as much as a year; if these are followed, they can account for substantial variations in marital fertility. Little research has been done on the determinants of post-partum abstinence. They are clearly cultural, in the sense that they characterize societies of interacting individuals, but they may also be linked to other factors.

Although differences in marriage patterns and breast-feeding patterns account for much of the observed differences in fertility across groups in pretransition societies, it is unlikely that their variation reflects variation in desired family size, for either the individual or the couple. Whether marriage was early or late, or whether breast-feeding was short or long, seems largely the outcome of other social concerns (Kreager 1982). It is probable that these patterns were determined by community norms or social structures, rather than individual preferences: Communities seem to have differed more in these respects than did individuals within these communities (Watkins 1991).


It is conventional to distinguish between fertility transitions in Western societies and those in other parts of the world. There are evident differences not only in geography but also in timing, with Western fertility transitions occurring earlier. In addition, fertility transitions in non-Western countries were promoted by an international population movement that played a major role in making modern contraception accessible in the Third World, whereas fertility declines in the West occurred without such efforts by governments or social movements. There have recently been a number of reviews of the determinants of fertility change; taken together, they show little consensus on similarities or differences in other determinants of fertility change (Hirschman 1994; Kirk 1996; Mason 1997), although most include mortality decline, the perception that large numbers of children are increasingly unaffordable, the attitudes and moralities concerning family life, and the costs of birth control (Casterline in press).

The earliest sustained fertility transitions at the national level occurred in France, where fertility decline began around the time of the French Revolution, and in the United States, where fertility control was evident in a number of New England communities by the end of the first quarter of the nineteenth century and widespread among women who married on the eve of the Civil War (David and Sanderson 1987). Other fertility transitions spread throughout Europe between 1870 and 1930 (Coale and Watkins 1986), with similar timing in Australia. These changes began in the core countries of northwest Europe and occurred later in the periphery of Central Europe and the Mediterranean countries. In contrast, most analysts agree that there was little evidence of efforts to deliberately stop childbearing or a decline in marital fertility anywhere in the developing world before 1960, except for Argentina, Uruguay, and Chile (largely populated by settlers from Western Europe).

The observation was nearly universal that industrialization was causing this decline, with those who were in more industrial settings (i.e., cities) having lower fertility than rural populations. Industrialization was thought to produce a rising standard of living, an increasingly complex division of labor, an open class system, a competitive social milieu, and individualism. These changes, most thought, induced a desire for smaller families (Hodgson and Watkins 1997). What most concerned observers of fertility changes was the differential fertility by class and ethnicity; the latter was particularly important in late nineteenthand early twentieth-century America, a period of massive immigration from Eastern, Central, and Southern Europe (Watkins 1994). Although some early observers saw the declining fertility of the wealthy and the urban as fostering prosperity, by the last quarter of the nineteenth century most emphasized the consequences of differential fertility for the composition of the population. For example, U.S. President Theodore Roosevelt decried the "race suicide" of upper-class women who were avoiding marriage or having small families: "The greatest problem of civilization is to be found in the fact that the well-to-do families tend to die out; there results, in consequence, a tendency to the elimination instead of the survival of the fittest" (1907, p. 550). At the time, eugenicists worried that the "prudent and thoughtful" would be the ones to practice birth control, while knowledge of birth control was unlikely to affect the fertility of the "reckless" lower classes (Hodgson and Watkins 1997, pp. 473–474). Women, according to most commentators, were the instigators of fertility decline, and many linked their turn to abortion and contraception to their reassessment of the value of motherhood. The problem was seen to be particularly acute among elite women. When initial attempts to persuade elite women to bear more children failed, attention was turned to persuading others to have fewer, and access to contraception was gradually liberalized. In Western countries the concerns of demographers and policy makers with domestic population composition faded with the widespread low fertility of the 1930s, and the eugenics movement was dealt a serious blow by its association with Nazi Germany in the 1930s and 1940s.

In the 1950s, Western attention turned to population growth rates in developing countries, many of which had until recently been colonies of Western countries. Mortality was declining, but until the 1960s, fertility in most developing countries was relatively high and apparently stable, aside from brief fluctuations associated with wars, famines, and other upheavals. This stimulated the formation of an international population movement, an alliance of neo-Malthusians, who emphasized the problems consequent on rapid population growth, and birth-controllers, who emphasized the importance of providing women with the means to control their reproduction. Subsequently, the previous pattern of stable reproduction came to an abrupt halt with the onset of rapid fertility transitions in a majority of countries. Between the early 1960s (1960–1965) and the late 1980s (1985–1990), the total fertility rate of the developing world as a whole declined by an estimated 36 percent—from 6.0 to 3.8 births per woman (United Nations 1995). Declines have been most rapid in Asia and Latin America (−42 and −43 percent respectively), less rapid but still substantial in the Middle East and North Africa (−25 percent), and almost nonexistent in sub-Saharan Africa. These averages conceal wide variations among countries in the timing of the onset of transitions and their subsequent pace. At one end of the spectrum of experience are a few countries (e.g., Hong Kong and Singapore) where a fertility transition started around 1960, followed by swift further reductions to the replacement level. At the other extreme are other countries, mostly in sub-Saharan Africa, that have not yet entered the transition.

These remarkable trends in reproductive behavior have been extensively documented in censuses and surveys, and the empirical record is not in dispute (Bongaarts and Watkins 1996). The causes of these trends, however, are the subject of often-contentious debate. Conventional theories of fertility decline, from the modernization versions dominant in the 1950s and 1960s to neoclassical economic and rational actor versions of recent decades, assume the fundamental importance of socioeconomic change, much as did nineteenthcentury theories about industrialization and fertility decline. Socioeconomic development results in shifts in the costs and benefits of children and hence in the demand for them. As desired family size declines, fertility reduction soon follows with the widespread adoption of birth control, especially when governments make contraceptive services available through family-planning programs. While this broad explanation is widely accepted, analysts vigorously debate the precise variables and processes involved in this chain of causation. These disagreements have been stimulating and fruitful, producing a wide variety of increasingly refined and detailed views that have guided empirical investigations.

Although rises in female marriage age have contributed to the decline in fertility, this decline is largely due to the adoption of new behavior in marriage: More precisely, it is due to the adoption of parity-specific control using modern contraceptives. In Europe, fertility declines were accomplished initially by the use of abortion, withdrawal, and/or abstinence by married couples to stop childbearing, and only later by the use of modern contraceptives to space children as well as to limit their number. In the Third World, fertility decline was closely associated with the use of modern contraceptives.

Why did fertility decline? Why did couples start to deliberately limit the number of children they bore? What are the "true" determinants of fertility? While a comprehensive theory of fertility would account for both the shift from high to low fertility and variations in fertility at each stage of the fertility transition, most of the attempts to understand the social, economic, and cultural influences on fertility have focused on attempts to understand the onset of the fertility transition. Almost anything that distinguishes traditional from modern societies has been considered relevant to the explanation of the fertility decline (Cleland 1985; see also reviews of fertility determinants by Hirschman 1994; Kirk 1996; Mason 1997).

The most influential theories that have guided demographic research into the determinants of fertility over the last four decades have been those that assume the fundamental importance of economic factor. Predominant in the 1960s and 1970s was the theory of the demographic transition (classic statements are Davis 1963; Freedman 1961–1962; Notestein 1953; Thompson 1929). Demographic transition theory is based on the assumption that the means of fertility control used in the early stages of the Western fertility transition were always known. Hence, fertility declines can be attributed to changes in the motivations of individuals or couples, changes thought to be related to "modernization," especially increasing literacy, urbanization, the shift to paid, nonagricultural labor, and declines in infant and child mortality. Neoclassical economic theory, and in particular the New Home Economics associated with Gary Becker (1991), provides a translation from macrolevel structural changes to the micro-level calculus of parents (for a more thorough review, see Pollak and Watkins 1993).

Empirical examinations driven by these theories gave them some support. It is now generally acknowledged that economic factors—often described in terms of the "costs" and "benefits" of children—are important determinants of fertility decline. It is, however, also acknowledged that economic factors do not provide a complete explanation. Currently, interesting research focuses on several additions to classical demographic transition theory and to neoclassical economic approaches.

Much attention has been devoted to evaluating the role of family-planning programs in the fertility decline in the Third World, where it seems that the methods used initially in the West were either not known or considered too costly in personal terms (Knodel et al. 1984). In the 1950s, it became evident that population growth rates in Third World countries were high because of declining mortality but stable fertility. This was believed to have substantial consequences, ranging from changes in the composition of the world's population (an increasing proportion of which was projected to come from Third World countries) to effects on Third World countries themselves, including famine, political instability, and the constraints that population growth was expected to place on the ability of these countries to develop economically and to modernize more generally. This led to concerted efforts by international agencies, Western governments, and Third World countries themselves to reduce fertility by making modern contraception desirable and accessible in the Third World (Hodgson and Watkins 1997). There has been considerable debate about the effectiveness of these efforts, with some according them little importance (e.g., Pritchett 1994) and others giving them more weight (e.g., Bongaarts 1997). There was a significant impact on fertility levels in the late 1980s, but whether this program effect operates primarily by affecting the timing of the onset of the transition or by the pace of fertility decline cannot be determined with available data (Bongaarts and Watkins 1996).

There has also been considerable interest in institutional determinants of fertility change. These are typically social institutions (e.g., systems of landholding) but occasionally are emergent properties of the collective behavior of individuals (Smith 1989). Therefore, in understanding the frequent association between education and fertility decline, for example, it may be more relevant to ask what proportion of the community has attended school than to ask whether a particular individual has. Similarly, both class relations and gender relations are aspects of the community rather than the individual, and both are likely to be associated with fertility change.

Another perspective emphasizes ideational change. Ideational changes are sometimes broadly, sometimes more narrowly, defined. Among the former is a shift in ideational systems toward individualism, which offered justification for challenging traditional authorities and practices, including those that concerned reproduction (Lesthaeghe 1983). In a similar vein, John Caldwell argues that much of the fertility decline in developing countries can be explained in terms of the introduction of images of the egalitarian Western family into the more patriarchal family systems of the developing world. It was not so much that the relative balance of costs and benefits of children changed, but that the moral economy shifted: It came to be seen as inappropriate to derive economic benefit from one's children (Caldwell 1982). Among the narrower ideational changes are reevaluations of the acceptability of controlling births within marriage (Watkins in press) and changes in the acceptability of modern family planning (Cleland and Wilson 1987). Explanations for fertility declines in terms of ideational change are often linked to a focus on diffusion as an important mechanism of change, where diffusion can be postulated as stemming from a central source such as the media (e.g., Westoff and Rodríguez 1995) and/or from person to person in global, national, and/or local networks of social interaction (Bongaarts and Watkins 1996). It is likely that personal networks influence fertility through social learning and the exercise of social influence (Montgomery and Casterline 1996). Intensive efforts to examine local networks of social interaction and their relation to fertility are currently underway in several countries (Agyeman et al 1995; Behrman et al. 1999; Entwistle et al. 1997).

What will happen to fertility in the future? In Western countries, fertility is close to replacement level, although in some (e.g., Italy, Spain) it is well below. There is less variation in fertility than there was either in pretransition societies or during the transition (Watkins 1991). Most couples desire only a few children (rarely more than two), and most use effective means to achieve their desires. Accordingly, analysts have concentrated on the determinants of fertility in specific subgroups of the population, such as teenagers or ethnic or racial minorities. In doing so, they have drawn on much the same combination of socioeconomic characteristics, institutional factors, and ideational change. For example, the higher fertility of teenagers is usually explained in terms both of their differing socioeconomic characteristics and of their lesser access to effective contraception, as well as to an unwillingness to use it.

Few expect fertility to rise, and there seems to be a consensus that fertility will either remain around replacement level or decline further (see, e.g., Lesthaeghe and Willems 1999). The predictions of even lower fertility in the West are based on a combination of proximate and true determinants. Since the 1960s, marriage age has risen sharply in most developed countries, as have divorce rates; if these trends continue—and as long as most children continue to be born within marriage—lower fertility will follow. There has also been some increase in the proportion who are unable to bear children, in part because some couples postpone marriage and childbearing so long that they are unable to have the children they want, and in part because it is likely that involuntary sterility associated with sexually transmitted diseases may have increased at least slightly (Menken 1985). But the major predictions of lower fertility in the future emphasize the characteristics of modern societies that make childbearing less rewarding compared to the other opportunities available to women and the continued inroads into the family that individualism is making (Keyfitz 1986; Preston 1986; Schoen et al. 1997).

Similarly, fertility is likely to begin to decline in Third World countries that have not yet begun a fertility transition and to continue to decline in those where this process has begun. The course of fertility decline in countries where fertility is now low suggests that once the process of the fertility transition has started, fertility levels decline monotonically until very low levels are reached. Moreover, there is no turning back: The new reproductive behavior is not abandoned. Thus, it is likely that past differences in fertility both within and across countries will diminish.

(see also: Demographic Transition; Family and Population Policy in Less Developed Nations; Family Planning; Family Policy in Western Societies; Family Size)


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