4

Posttransition Fertility

By 1995, half of the world's 5.7 billion people lived in low-fertility countries, in which fertility was under 2.5 children per woman. Most lived in countries in which fertility was at or below replacement level (i.e., approximately 2.1 children), and a large minority (15 percent of the world total) lived in countries in which fertility was well below replacement level (below 1.8 children). What will happen in the future? Do the lowest levels of contemporary fertility portend the future for most countries? Will fertility decline even further toward zero in the 21st century, driven by the same forces that produced the fertility transition? Or will homeostatic mechanisms raise fertility back toward replacement level, or even higher? Will countries now in transition stabilize at fertility levels well above two children per woman, or below? The answers to these questions are central to projecting future population trends.

We address these questions below and reach two broad conclusions:

  • Stabilization levels for countries now in fertility transition or not having started it will be similar to those observed in contemporary low-fertility countries, around or somewhat below two births per woman. Just as fertility varies by a fair amount across today's low-fertility countries, those countries currently in transition are also likely eventually to experience varying, albeit generally low, fertility levels.

  • In all countries, once low fertility levels are reached, further fertility change is largely indeterminate. For any given date in the future, fertility levels are quite unpredictable, and substantial variability is likely. Nevertheless, some limits to possible variation can be set, because low-



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BEYOND SIX BILLION: Forecasting the World's Population 4 Posttransition Fertility By 1995, half of the world's 5.7 billion people lived in low-fertility countries, in which fertility was under 2.5 children per woman. Most lived in countries in which fertility was at or below replacement level (i.e., approximately 2.1 children), and a large minority (15 percent of the world total) lived in countries in which fertility was well below replacement level (below 1.8 children). What will happen in the future? Do the lowest levels of contemporary fertility portend the future for most countries? Will fertility decline even further toward zero in the 21st century, driven by the same forces that produced the fertility transition? Or will homeostatic mechanisms raise fertility back toward replacement level, or even higher? Will countries now in transition stabilize at fertility levels well above two children per woman, or below? The answers to these questions are central to projecting future population trends. We address these questions below and reach two broad conclusions: Stabilization levels for countries now in fertility transition or not having started it will be similar to those observed in contemporary low-fertility countries, around or somewhat below two births per woman. Just as fertility varies by a fair amount across today's low-fertility countries, those countries currently in transition are also likely eventually to experience varying, albeit generally low, fertility levels. In all countries, once low fertility levels are reached, further fertility change is largely indeterminate. For any given date in the future, fertility levels are quite unpredictable, and substantial variability is likely. Nevertheless, some limits to possible variation can be set, because low-

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BEYOND SIX BILLION: Forecasting the World's Population fertility countries are unlikely to experience sustained fertility well above two children per woman, and homeostatic mechanisms have the potential, with considerable lag, to counteract very low fertility. FERTILITY LEVELS AND PAST TRENDS For perspective, we begin with a description of recent (post-1950) fertility in posttransition countries, i.e., in countries in which fertility control is widespread and aggregate total fertility1 in 1995 was around two children per woman, more specifically under 2.5 children. Among these low-fertility countries were all the countries of Europe except Albania, as well as Northern America, Japan, Australia, and New Zealand. Combined, the 42 industrial, low-fertility countries contain 21 percent of world population. Two out of three of these countries actually had fertility levels under 1.8 children, or well below levels needed for population replacement (Table 4-1). In the developing regions, low-fertility countries are geographically dispersed. China, with 22 percent of world population, is the largest country in this group. Eighteen other countries, from the Caribbean to Central Asia, add 9 percent of world population to the low-fertility group.2 Fertility was above 2.1 (but below 2.5) in more than half of these developing countries. Figure 4-1 shows the path these countries have taken to these low levels. For the Asian low-fertility countries, fertility had to decline dramatically between 1950 and 1995 to reach low levels. For the current low-fertility countries of Latin America and the Caribbean, fertility declines were also sharp, although less dramatic. For the industrial countries, fertility decline has been more moderate. These countries include the only 11 countries that had low fertility in 1950. In fact, most industrial countries have been at or somewhat close to low-fertility levels since that date. 1   To measure fertility levels and changes, we use the total fertility rate (TFR), calculated by summing age-specific rates for women aged 15-49 in a given time period. Attractive features of this measure include its wide availability, straightforward interpretation (i.e., the number of children a hypothetical group of women would bear if they experienced these rates over their reproductive lifespan), and standardization on the age structure of women of childbearing age. We later discuss the quantum and timing components of such period-fertility measures. The specific rates on which the discussion is based are, strictly speaking, for the period 1990-1995. 2   Zeng (1996) argues that important Chinese data sources underestimate fertility. Nevertheless, after adjusting for underreporting, he estimates that Chinese fertility was still at about the replacement level in 1990-1992.

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BEYOND SIX BILLION: Forecasting the World's Population TABLE 4-1 Low-fertility countries by region, their populations, and their shares of world population, by level of total fertility, 1990-1995   No. of countries Population (millions) Percent of world population   Total fertility: Total fertility: Total fertility: Region <2.5 <2.1 <1.8 <2.5 <2.1 <1.8 <2.5 <2.1 <1.8 Industrial regions 42 38 28 1,168 1,158 796 20.6 20.3 14.0 Eastern Europe 10 9 7 310 306 262 5.5 5.4 4.6 Northern Europe 10 9 5 93 93 71 1.6 1.6 1.3 Southern Europe 10 9 7 140 138 127 2.5 2.4 2.2 Western Europe 7 7 7 181 181 181 3.2 3.2 3.2 Northern America 2 2 1 297 297 30 5.2 5.2 0.5 Australia/New Zealand 2 1 0 22 18 0 0.4 0.3 0.0 Japan 1 1 1 125 125 125 2.2 2.2 2.2 Developing regions 19 9 5 1,711 1,346 60 30.2 23.7 1.1 China 1 1 0 1,221 1,221 0 21.5 21.5 0.0 Other East Asia 4 3 2 74 52 45 1.3 0.9 0.8 South Asia 3 2 1 80 62 3 1.4 1.1 0.1 West Asia 2 0 0 316 0 0 5.6 0.0 0.0 Caribbean 7 3 2 17 12 11 0.3 0.2 0.2 South America 2 0 0 4 0 0 0.1 0.0 0.0 Total 61 47 33 2,879 2,503 856 50.8 44.0 15.1 Source: United Nations (1999).

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BEYOND SIX BILLION: Forecasting the World's Population FIGURE 4-1 Past and projected total fertility in low-fertility countries, 1950-2050. SOURCE: Data from United Nations (1999). Nevertheless, the industrial countries also show relatively substantial fertility decline, as well as some heterogeneity. Total fertility for the group as a whole fell from 2.5 children in the 1950s to below 2.1 in the early 1970s to approximately 1.7 in the early 1990s.3 Declines were most dramatic in the late 1960s and early 1970s. These declines were pervasive, taking place in Northern America, Japan, Australia and New Zealand, and all subregions of Europe (United Nations, 1999:Table A-20). Most regional declines were over one birth. Somewhat smaller declines were registered only in regions that had lower fertility to begin with, particularly Northern and Western Europe. By 1990-1995, with all the industrial regions below levels needed for population replacement, fertility remained highest in Northern America (2.02), Australia and New Zealand (1.91), and Northern Europe (1.81). 3   For many of these countries, using 1950-1960 as a referent can be problematic because of what many see as the unique set of circumstances that produced fertility increases following World War II. This baby boom peaked around 1960. At this peak, fertility was higher, for a number of European countries, than it had been in the 1920s and 1930s.

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BEYOND SIX BILLION: Forecasting the World's Population The particular countries with fertility levels above 2.0 are a heterogeneous group. In addition to Albania, they include Macedonia, Moldova, Sweden, Iceland, New Zealand, and the United States. Likewise, countries with the lowest fertility, below 1.5 children (as of 1990-1995), are not obviously similar: Germany (especially the former East Germany), Austria, Slovenia, Greece, Italy, and Spain. More recent evidence indicates that Russia and Japan have joined this group. We see little evidence that the richest countries in the industrial world have the lowest fertility, or the highest. Thus the experience of low-fertility countries over the last few decades has been heterogeneous and not necessarily easy to project. Internally, fertility levels in these countries may also be heterogeneous. Ethnic and racial differences in fertility (which may partly account for fertility variation across societies) to some extent reflect the socioeconomic standing of different groups, but can also reflect long-standing differences. The contrasts in fertility in the United States between European-origin whites and African Americans, for example, have been relatively stable for three decades and are not entirely socioeconomic in origin (Swicegood and Morgan, 1994). These differences also reflect contrasts in gender relations and marriage and family institutions between ethnic groups. Many other examples exist of minority-majority group relations that involve fertility differences. These fertility differences may have a long history, as with the high fertility of ultraorthodox Jews in Israel (Friedlander and Feldmann, 1993), and may be rooted in distinctive cultures and promoted for political reasons, as with Malays, Chinese, and Indians in Malaysia (Govindasamy and DaVanzo, 1992). PROJECTED FERTILITY TRENDS Figure 4-1 also shows the trends the U.N. projects for future fertility in low-fertility countries. These trends are quite similar across countries. The similarity is produced by standard projection procedures that allow relatively minor variation. Projection Methods To project fertility where it is now at or below the level required for population replacement, the U.N. allows any trend in total fertility to continue for one 5-year period, and then requires fertility to change by 0.07 children every 5-year period until it reaches a predetermined level at which it is kept constant. This level is defined as 1.9 children, for countries in which fertility is between 1.5 and 2.1 children, or 1.7 children, for

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BEYOND SIX BILLION: Forecasting the World's Population countries in which fertility is under 1.5 children (Zlotnik, 1999). 4 In long-run projections to 2050, the distinction between stabilization levels of 1.9 and 1.7 produces the only meaningful country variation. 5 Countries that have not reached low levels of fertility are assumed to eventually stabilize at levels that would produce approximate replacement of the population (assumed by the U.N. to be 2.1 children per woman). How soon they reach that level is a complex question resolved subjectively, taking many factors into account (see Chapter 3). Alternative projections from the World Bank are quite similar, although slightly simpler. Countries that have fertility below two children per woman are assumed to stay at their current levels for two 5-year periods, and then return to replacement level (around 2.1 children, but calculated exactly taking mortality into account), following a linear path, by the year 2030. Countries that are above the replacement level are assumed to reach it eventually, the timing depending on current level and the past pace of declines (see Chapter 3). In a few cases in which recent fertility declines have been particularly rapid, fertility is allowed to dip below the replacement level before returning to that level. Once the replacement level is reached, fertility stays at that level, although it continues to vary slightly as mortality changes. Neither agency makes systematic use of time-series approaches in projecting fertility (e.g., Carter and Lee, 1986; Thompson et al., 1989; Alho, 1992). While something can be learned from such models, particularly with regard to the future variability of fertility (see Chapter 7), their broad application is limited by data needs and demanding procedures, and they do not obviate the need to exercise judgment. The Assumption of Falling Fertility The U.N. and World Bank approaches return us to two questions raised earlier: whether it is reasonable, as both assume, for high or moderate fertility always to decline to replacement level or below, and whether subsequent fertility should be kept constant, and if so at what level. The first issue is considered in this section, the second in the remainder of the chapter. 4   Cohort fertility may be taken into account in a limited manner. Where completed fertility is known for women born in 1962, the stabilization level is instead the average of this figure and either 1.9 or 1.7. What is described is the medium-variant U.N. projection. High and low variants assume stabilization levels that are 0.4 children higher or lower, but 0.5 children higher or lower for countries that have not reached replacement. 5   The U.N. assumes an eventual return to replacement in all regions in its long-range projections, beyond 2050. This assumption acknowledges the likely operation of homeostatic mechanisms over the very long term.

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BEYOND SIX BILLION: Forecasting the World's Population TABLE 4-2 Classification of countries by total fertility in 1950-1955 and 1990-1995   Total fertility 1950-1955   Total fertility 1990-1995 4.5+ 3.5-4.4 2.5-3.4 Under 2.5 Total 4.5+ 66 1 0 0 67 3.5-4.4 20 0 0 0 20 2.5-3.4 28 3 1 0 32 Under 2.5 17 11 24 12 64 Total 131 15 25 12 183 Source: United Nations (1999). The assumption that fertility, in high-fertility countries, will eventually fall close to two children per woman is generally supported by previous experience. In few countries has fertility decline, once started, paused for more than a few years at intermediate levels. Once past these levels and down close to replacement level, fertility has never moved back up and stabilized at substantially higher levels. Countries currently in transition give no indication either of fertility stabilizing at high or intermediate levels. Table 4-2 illustrates these points, showing how fertility changed from 1950-1955 to 1990-1995. Of the 12 countries with low fertility (under 2.5 children) in the 1950s, all still had low fertility in the 1990s. The same point could be made if other periods had been selected. For instance, of the 32 countries in 1970-1975 with low fertility, all still had low fertility in 1990-1995. Thus no precedent exists for a low-fertility country to return to persistent fertility levels well above two children per woman. Consider next the 25 countries with intermediate fertility (2.5-3.4) in 1950-1955. Of these, 24 had low fertility by 1990-1995. Only Argentina did not achieve low fertility: its total fertility was 3.2 in 1950-1955, 3.1 in 1970-1975, and 2.8 in 1990-1995. The reasons for Argentina 's apparent stabilization at this intermediate level (or at least very slow decline) are unclear. Such apparent stabilization above two children per woman must be characterized as rare. Of the 15 countries with moderately high levels of fertility (3.5-4.4) in 1950-1955, all but one moved to lower fertility, with most achieving low fertility under 2.5 by 1990-1995.6 The one exception was Gabon, where 6   The three countries whose fertility declined only into the intermediate range (2.5-3.4) were Israel, the Bahamas, and Jamaica. All three show clear evidence of recent fertility decline, suggesting that fertility in these countries has not yet reached a stable level.

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BEYOND SIX BILLION: Forecasting the World's Population fertility in the 1950s and 1960s had been substantially depressed by pathological subfecundity and infertility. Even the countries with high fertility (4.5 or higher) in 1950-1955 had substantially lower levels by 1990-1995. For these countries, much of the transition remains unobserved, but its inevitability, based on the experience of other countries, seems clear. Except possibly in rare cases, fertility will not stabilize at levels well above two children per woman. Instead, it will continue to decline, although at an uncertain pace, until levels close to two children per woman are reached.7 Projection Accuracy While the general trend therefore appears well established, specific future levels are difficult to predict. Figure 4-2 shows the error in projected total fertility, beginning with periods when total fertility was below 2.5. The “combined” error is averaged across all countries with these low levels of fertility in eight separate U.N. and World Bank forecasts. Fertility has on average been overprojected. Forecasters have anticipated less fertility decline than took place, even at these low levels. Projected fertility decline has fallen short of actual decline to a greater degree, in fact, than for developing countries earlier in fertility transition. In 20-year projections, for instance, projected total fertility has been on average 0.39 children too high, whereas in cases in which initial total fertility was above 2.5, projected total fertility was on average 0.27 children too high (see Table 3-1). The overprojection has been greater, however, when fertility was closer to 2.5 than when it had already declined further.8 While forecasters therefore have had a good understanding of the general downward trend in fertility, they have not had a precise grasp of the pace of decline. Current projections presumably also incorporate some uncertainty. This can be estimated from the results of past forecasts using 7   For additional evidence of persistent decline once a transition is under way, see Bongaarts and Watkins (1996). A counterargument is that countries currently with high fertility are predisposed in that direction and fundamentally different from those that have completed the transition. The same argument about the imperviousness of high-fertility levels has been made in the past, in the 1950s, for instance, about South Korea, and in the 1970s about Bangladesh. The argument has not held up. The pace of decline in countries starting transition later could be slower, as suggested in Chapter 3, but all the evidence suggests that, eventually, low fertility will be reached. 8   This upward bias does go together with greater precision, given that fertility at low levels varies within a narrower range. Absolute error in projected total fertility averages 0.29 in 10-year projections and 0.41 in 20-year projections, as contrasted with 0.57 and 0.79 at higher initial fertility levels (see Table 3-1).

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BEYOND SIX BILLION: Forecasting the World's Population FIGURE 4-2 Error in projected total fertility averaged across countries and forecasts, for cases in which the initial level was under 2.5. SOURCE: See Appendix B. Error is defined as the difference between projected total fertility and the current estimate. ex post methods, as illustrated in Chapter 7 (see Figure 7-4). At least as important for improving projections, however, is understanding the characteristics of fertility trends and the reasons for them. INTERPRETING FERTILITY TRENDS At low fertility levels, fertility trends have had three important characteristics. First, in the main they are best characterized as period trends as opposed to cohort ones. That is, they have not reflected the changes in fertility due to one cohort or generation of women with different tendencies succeeding another. Instead, they have reflected contemporaneous changes in fertility, in given periods, by women of all ages. Different cohorts do end up with different numbers of births, spaced differently, but period factors can generally explain these contrasts. Second, fertility trends have involved both reductions in the total

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BEYOND SIX BILLION: Forecasting the World's Population numbers of births that women have and changes in the timing of these births. Third, the births reduced in number have been mainly third, fourth, and higher-order births rather than first or second births. Much of the apparent decline in first and second births can be attributed to delay or postponement. We discuss these characteristics specifically with reference to industrial countries. Although we anticipate that fertility in demographically advanced developing countries will have similar characteristics, these countries have not been at such levels long, so relevant data are limited. Period Versus Cohort Effects Changes in post-1950 fertility in industrial countries were largely period-driven. In calendar years when fertility increased, it did so for all age groups; when it declined, the decline was pervasive (Ni Bhrolchain, 1992; also see Brass, 1974; Page, 1977; Namboodiri, 1981; Pullum, 1980; Rindfuss and Sweet, 1977; Sweet and Rindfuss, 1983; Rindfuss et al., 1988; Foster, 1990). The pattern of change suggests that the unique experiences of birth cohorts were not highly relevant for fertility change.9 Highly plausible arguments for cohort influences on fertility have been made by Ryder.10 Surely the shared experience of each generation of parents should shape their fertility. For example, a war should have a distinct and lasting impact on the generation at the age of enlistment. In addition, it is argued, people of different ages react differently to contemporaneous events. While younger people may adopt innovations aggressively, older people are less able and willing to change. Their past experience and their investments in the status quo reinforce their inertia. Despite the appeal of these arguments, attention to cohort processes generally does not help clarify aggregate fertility trends. Fertility change can be so rapid that it cannot be accounted for by the replacement of one cohort by another. More parsimonious explanation usually comes from positing powerful period effects that produce pervasive changes across all cohorts simultaneously. 9   Likewise, demographic models of cohort-specific age patterns of behavior have not provided accurate predictions of cohort levels of childlessness and nonmarriage (see Chen and Morgan, 1991; Rodgers and Thornton, 1985). 10   Ryder argues that a cohort perspective is crucial not only to understand fertility (Ryder, 1964, 1986) but also to understand social change generally (Ryder, 1965). Demographers' bias toward cohort approaches may account for their consistent tendency (see Freedman, 1986a, 1986b) to underestimate the speed of social change.

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BEYOND SIX BILLION: Forecasting the World's Population Could fertility intentions reflect a cohort dimension that could bring more certainty to future predictions? A brief review of the use of data on fertility intentions provides little optimism. In the 1960s, U.S. researchers investigated women's future fertility intentions as indicators of completed cohort fertility. For instance, if a 25-year-old woman had one child and responded that she intended to have two more children, then demographers projected her completed family size as three. Her intentions could reflect relatively stable cohort-based plans that, in time, would be acted on. Initially, the predictions worked. Despite substantial errors at the individual level, for a series of birth cohorts such errors canceled each other, leaving aggregate cohort predictions on target. However, beginning with cohorts born in the 1940s and 1950s, errors at the individual level cumulated to produce estimates of fertility that were much too high (Westoff and Ryder, 1977b). A plausible explanation for this failure of prediction is that those asked whether they wanted another child assumed that social conditions would not change radically. Answering this question in the 1960s and early 1970s, most did not anticipate how antinatalist forces would dominate in the following years. Their fertility intentions, therefore, were no more predictive than their concurrent fertility behavior (Westoff and Ryder, 1977a, 1977b). One cannot tell if fertility postponed will be realized (a timing shift) or forgone (a quantum shift).11 Further, the life-course perspective suggests that delay may allow period influences to operate, as couples accumulate experience that leads first to uncertainty about additional children and eventually to a decision to revise future fertility downward. Thus, if one must use fertility-intention data to provide guidelines to future fertility, one must do so with great care. Certainly, the assumption that such responses reliably predict cohort reproductive behavior is not consistent with available evidence. Despite this evidence, many forecast agencies in industrial countries, while acknowledging the importance of period effects, also monitor cohort fertility. For instance, some extrapolate completed cohort fertility, in addition to total fertility. They assume that a smooth time series for completed cohort fertility reflects long-term structural changes, and that total fertility fluctuates around that long-term trend. Whether this added indicator is useful for long-term forecasts remains an open question. 11   Bongaarts (2000:Figure 3) shows that, for a set of 14 low-fertility countries, the current period fertility is well below reports of desired family size. It is unclear whether fertility will be made up in the future (i.e., at older ages) or if individuals will have fewer children in their life than they desired at a younger age.

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BEYOND SIX BILLION: Forecasting the World's Population societies, such drastic policies are not likely either now or in the future.13 Other initiatives to support childbearing have been reviewed by Demeny (1986; see also Teitelbaum and Winter, 1985), who describes their consequences as “nil or negligible.” Some programs, nevertheless, have had at least modest effects. For instance, in 1976 East Germany introduced a set of targeted subsidies that apparently increased the proportion of women having a third child (Buttner and Lutz, 1990). At least as important is evidence that public policies that are not deliberately pronatalist can have the unintended consequence of increasing fertility. The evidence includes the positive effects of the U.S. program of Aid to Families with Dependent Children (AFDC) on the fertility of poor women (National Research Council, 1998); the modest positive effects on the fertility of poor women of restrictions on public funding for abortion (Cook et al., 1996); the modest positive effects on marital fertility of increasing the U.S. income tax deduction for dependents (see Whittington, 1992); and the effects on Swedish fertility in the late 1980s and early 1990s of maternal leave policies that encouraged closely spaced births (Hoem, 1990). Policies such as these contribute to a social setting that supports multiple roles for women and reduces the conflict they feel between raising a family and pursuing other interests. As argued earlier, such a setting appears to facilitate slightly higher fertility, closer to two children per woman, in some industrial countries. Although the link between a favorable setting and specific public policies is not always clear, policy can certainly contribute in various ways. Free or subsidized child care, reduced taxes for families with children, paid parental leaves, subsidized housing for families with children, etc., all reduce the economic costs of childrearing and could collectively have some fertility effect. The public discussion of such issues could be as important as the enactment of policy. Public debate could be seen as reaffirming or reconstructing an ideology supportive of parenthood. The enactment of such policies could signal that the society acknowledges the social value of parenthood and assigns a high status to parents. Such ideas, if they were supported by influential elites, could play a role in stabilizing fertility, 13   More limited decisions regarding access can also have subtle effects. In the United States, abortion restrictions, such as the Hyde Amendment, have severely limited federal funding for poor women's abortions. More generally, the antiabortion movement has sought to stigmatize abortion providers and patients, reducing the number of health facilities that perform abortions. The result has been slightly higher fertility, particularly among poor women. These efforts were aimed not at increasing fertility but at reducing abortion.

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BEYOND SIX BILLION: Forecasting the World's Population just as other ideas were influential in the timing and pace of fertility transition (Chapter 3). Thus, the indirect effects of policy debates may be as important as the direct effect of economic relief for parents. A basic reason why policy could have some effect is that, in most contemporary low-fertility settings, young women on average still say they expect to have two children (Bongaarts, 2000). Their expectations may be socially determined, and the realization of these expectations may become constrained by various factors; in any case, actual fertility eventually falls short. To some extent policy and programs can help relax constraints: allowing institutional flexibility through family leave, for instance, or encouraging institutional innovation by way of workplace child care centers. Policy that removes obstacles to achieving fertility desires could raise actual fertility, although presumably no higher than desired levels, which are now close to replacement level. A somewhat different kind of policy impact may be important in other countries, such as China. China's state policy has obstructed the achievement of fertility desires, and the problem then becomes one of assessing the possible impact of a withdrawal of this aggressive policy. The future of the policy is substantially uncertain. Concerns are increasingly being raised about the rapid increase of the elderly population and the unavailability of children to care for them. In addition, the one-child policy may become increasingly difficult to implement because socioeconomic policies have vastly increased the mobility of the Chinese population. Such mobility not only loosens the ties between children and parents but also reduces the ability of the state to monitor and control individual fertility. FUTURE TECHNOLOGICAL DEVELOPMENTS Besides the potential role of new policies, several technological developments may, in the future, help couples more closely approximate their fertility desires: Contraception. Over the last few decades, improvements in techniques of contraception and abortion have facilitated fertility declines, particularly in developing countries. Further improvements are possible, given that current methods have side effects, allow for imperfect use, and leave many unwanted and mistimed pregnancies. Improvements may have significant benefits for women and possible fertility effects. Proception. A potentially more significant issue for fertility levels in industrial countries, however, is the technology of proception (Miller, 1986), which helps people have babies. Such simple proceptive techniques as more frequent intercourse and selecting the right time for intercourse

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BEYOND SIX BILLION: Forecasting the World's Population could have some effect. More important, in the long run, may be techniques of hormone therapy and in vitro fertilization, which should become more effective. With childbearing being increasingly delayed to later ages, when fecundity is lower—it decreases dramatically between ages 35 and 45—developments in proceptive technology could prevent fertility levels from dropping more sharply than they might.14 Sex selection. Another likely technological development, expectable within a decade or so, involves more efficient and effective methods for determining the sex of one's offspring. Sex selection is relevant for fertility levels in such low-fertility developing countries as China and South Korea and could become important elsewhere. In the absence of sex selection, a strong preference for sons or daughters can increase fertility substantially, as couples have more children in order to reach their desired quota (Bongaarts and Potter, 1983:Chapter 9). This effect could be reduced or eliminated if new techniques become available. At present, only selective abortion is a viable sex-selection technique. This procedure is expensive, invasive, and for some morally problematic. In addition, the procedure does not guarantee another birth of the desired sex. Couples who desire sons (or daughters) may require multiple abortions to achieve a desired sex composition. Alternative methods that are also effective could dramatically lower the costs of realizing sex preferences. Effective methods would mean that fewer children would be needed to obtain the desired number of sons. This would produce unbalanced sex ratios (Park and Cho, 1995), with various fertility effects. Unbalanced sex ratios in favor of males result in increases in the level of fertility required for replacement. The preference for boys over girls does vary across societies and over time and could change if undesirable social consequences ensue. While ignoring sex preferences seems unwise, projecting unbalanced sex ratios far into the future carries considerable uncertainty. Genetic selection. Whereas the 20th century has given people control over the number of children they have, the 21st century could bring control not only over the sex but also over the entire genetic makeup of children (Gill et al., 1992). Gene therapy may lower the risk of certain diseases in one's offspring and thus reduce uncertainty about their health. Technology that would allow cloning of humans may become available. 14   Data from the 1995 U.S. National Survey of Family Growth (NSFG) indicate that 2 percent of all women aged 15-44 report a visit for medical help to get pregnant or to prevent miscarriage in the 12 months prior to the survey; an additional 13 percent report a visit in previous years (Abma et al., 1997:Table 56).

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BEYOND SIX BILLION: Forecasting the World's Population Some might find the biological closeness of such children as an advantage. More distant possibilities allow selection of desired characteristics from different individuals, via genetic engineering, in order to give one's child maximum genetic potential. Or it may be possible to have much of the period of gestation take place outside the womb, reducing the costs, and pleasures, of pregnancy. The effects of such technological developments are difficult to assess. If one could define precisely the kind of child one wants, perhaps one child would be enough. If multiple types of parenthood become possible, having children might become more appealing to diverse individuals with varying lifestyles. The fertility impact of such technology is not easily assessed. CONCLUSIONS Future Levels and Trends We began by asking where fertility is headed in the 21st century, both among developing countries as they complete their fertility transitions and among industrial countries. Our conclusion has two parts. First, fertility in countries that have not completed transition should eventually reach levels similar to those now observed in low-fertility countries—around or somewhat below two births per woman, but with substantial variation across countries. Second, specific levels for these countries, and ultimate levels for industrial countries, are largely indeterminate for a variety of reasons. Nevertheless, these ultimate or long-term levels are unlikely to be either well above, or well below, two children per woman. Our first conclusion relies heavily on interpreting the experience of the diverse set of countries that have made the transition to low fertility. In hardly any of these countries has fertility stabilized at rates well above two children per woman. Such an event would be dependent on substantial proportions of higher-order births, but higher-order births are largely anachronistic in industrial-country settings. Parents in such settings find sufficient emotional, psychological, and social rewards from having one or two children, and only occasionally three. Since they also bear most of the economic and emotional costs of childrearing, only massive societal transfers could conceivably compensate them for the trouble and the lost opportunities of raising a large family. This is true for the majority in most industrial countries, but the countries are otherwise diverse, and the specific levels of fertility they have reached, although all close to or below 2.0, still differ. These countries therefore provide a spectrum of fertility experience within which countries still in transition will probably fall.

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BEYOND SIX BILLION: Forecasting the World's Population Where fertility will fall, within this spectrum, will depend on decisions relating to first and second births. Fertility is unlikely to rebound significantly, given the increasing irrelevance of higher-order births. But fertility could fluctuate, for many reasons. Idiosyncratic economic and political events could dramatically change the social environment and the way it is viewed. This happened in the 1950s and 1960s with the unanticipated postwar baby boom. Even with current demographic expertise, that event would not have been anticipated, and other similar events could certainly occur in the future. Further steep falls in fertility to very low levels are possible but unlikely to be sustained. Homeostatic mechanisms may begin to operate, although possibly with considerable lags. Societies have the capability to encourage and reward childbearing, by providing incentives or by removing disincentives for behavior that has social benefits (Blake, 1972, 1994). In various ways, industrial societies already provide various rewards, but using them to deliberately manipulate fertility is a sensitive issue, potentially involving substantial economic transfers, and likely to be contested. Whether such policies will be adopted in specific countries depends on the indeterminate outcome of political struggles that are difficult even to visualize at this time. Even if such policies were adopted, the fertility response would not be fully predictable. The fertility response depends partly on fertility preferences, since policies that facilitate the achievement of preferences are much more likely to be successful than policies that attempt to reshape preferences. The importance of preferences is likely to grow in the future, given improvements in contraceptive and proceptive technology. The preference for two children is still extremely common even in low-fertility countries, but the future course of such preferences is difficult to predict. These preferences change in response to societal evolution and economic conditions. They do not appear to be stable cohort characteristics. Some now argue that changes in fertility preferences are tied to changes in values, but how values themselves will change in the future is unknown. The ultimate trend in fertility at low levels, therefore, remains largely indeterminate. This discussion has few implications for changing the way posttransition fertility is currently projected. Fertility projection strategies generally build on the fundamental insight of the inevitable and irreversible decline in fertility to low levels and the expected long-term maintenance of fertility close to or below two children per woman. This strategy does not appear to have any fundamental flaw and, despite its failure to provide much differentiation in trends across countries, is difficult to improve on.

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BEYOND SIX BILLION: Forecasting the World's Population Research Priorities Any future improvement will require new research. Studies are needed of countries in transition in order to assess our conclusion that they will move to fertility levels approximating two children per woman. As noted above but argued at length in Chapter 3, developing countries that now have low fertility are a select group. Are those still in transition fundamentally different in ways that could perhaps produce fertility stabilization well above levels required for population replacement? Despite the substantial record of research on the determinants of posttransitional fertility, some issues have been relatively ignored but are important for predicting future trends. We particularly need to know more about what socioeconomic and biological factors are most predictive of very late and very low childbearing. For example, the causes of childlessness—a key factor for fertility projections —are not well understood. Is it largely a matter of choice, or are the difficulties of getting pregnant and carrying a pregnancy to term major obstacles to childbearing for women aged 35 and older? Will the age at childbearing continue to rise, and will this trend be accompanied by increasing childlessness? A closely related issue, the formation of sexual unions, has been understudied. Given the increasing importance of sequential unions, we need to know more about the possibly offsetting effects of fertility reduction due to time spent outside unions and fertility increase due to the desire for additional children in new unions. Studies are needed to assess the impact and costs of various fertility-enhancing mechanisms that governments could consider if they become concerned about the adverse consequences of low fertility. Given that future policies are likely to be national in scope, comparative national studies and internationally comparable data on this issue become increasingly important. While high fertility will become increasingly isolated geographically and within societal subgroups, studies of groups that maintain high fertility could identify conditions that can raise levels of very low fertility closer to two children per woman. Descriptions of such groups could provide a valuable comparative perspective on the dominant, low-fertility pattern. REFERENCES Abma, J.C., A. Chandra, W.D. Mosher, L. Peterson, and L. Piccinino 1997 Fertility, family planning, and women's health: New data from the 1995 National Survey of Family Growth . Vital Health Statistics (National Center for Health Statistics) 23(19).

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