Malcolm Potts & Martha M Campbell. New Dictionary of the History of Ideas. Editor: Maryanne Cline Horowitz. Volume 5. Detroit: Charles Scribner’s Sons, 2005.

Perceptions of the meaning, implications, and control of reproduction and sexuality, at both the individual and community levels, are among the most important, but also the most challenging, in the history of ideas. Changes in human population helped shape the twentieth century and are creating new tensions in the twenty-first, but, despite the profound significance of childbearing to individuals and the impact of population change on economics, politics, maternal and infant health, the environment, and national security, the intellectual history of population is oddly fractured and frequently uninformative. There are still divisions on the exact mix of factors, such as vaccination and socioeconomic change, driving the dramatic fall in death rates that pushed the global population from 1,650 million in 1900 to 6,071 million in 2000, and there is no consensus on the factors driving falling birth rates in recent decades. Many societies have made pragmatic decisions about their citizens’ access to modern contraception and safe abortion, but bitter and painful differences on ethics persist. The two most important shifts in the intellectual history of population—the Papal encyclical Humanae vitae and the Chinese “one-child” policy—represent diametrically opposed responses to population change.

An understanding of population must draw on reproductive biology, anthropology, economics, political science, and demography, as well as knowledge of cultural and religious beliefs, but cross-disciplinary progress has been slow. As Charles Darwin (1809-1882) acknowledged, Thomas Robert Malthus’s (1766-1834) An Essay on the Principle of Population, published in 1798, was the intellectual trigger for The Origin of Species (1851). In the second half of the twentieth century, biological perspectives began to influence ideas about population change. Anthropologists reconstructed the demographic history of preliterate communities, which have been characteristic of the hunter-gatherer way of life for more than 95 percent of the time Homo sapiens has been a distinct species. In such societies, women sometimes do not menstruate until they are eighteen or even twenty years old, and pregnancies are well spaced by natural endocrine changes associated with breast-feeding. The average woman has six to eight pregnancies, half of which usually die, with the consequence that hunter-gatherer populations grow slowly.

The second half of the twentieth century saw unprecedented and unrepeatable changes in the growth of the global population. Rising potential fertility, as a result of changes in breast-feeding and the age of puberty, together with a rapid fall in death rates, pushed population growth rates up. The highest absolute growth in global population occurred in the mid-1980s, with more than 85 million more births than deaths per annum. During the same period, developed countries finally gained wide access to contraception and safe abortion, and in some regions average family size fell below two. In parts of Asia, which formerly had large families, the birth rate also fell to replacement level or below, although elsewhere in Asia and in Africa birth rates remain high. The implications for the health of women and children, for economic prosperity, social stability, and the environment of these changes are profound, yet some of the most important population changes were not predicted by most demographers.

The standard theory of the demographic transition was that a fall in the birth rate would lag behind any decline in the death rate and that birth and death rates would slowly stabilize as couples grew richer, became more educated, and made a rational decision to have smaller families. Frank Notestein, the distinguished American demographer, gave articulate expression to the theory. As the volume of empirical data on family planning has increased, so demographers have defined the proximal determinants of family size with increasing accuracy. These are the age at commencing intercourse, the prevalence of pathological causes of infertility, the suppression of ovulation associated with lactation, and use of contraception and abortion. However, the more distal determinants that make birth rates decline continue to be debated. The Office of Population Research at Princeton University explored the history of fertility decline in various parts of Europe and found that ideas about family planning spread by diffusion in homogeneous political and religious groups.

Clash of Ideas

The United States led the way in research that produced oral contraceptives and a new generation of intrauterine devices (IUDs) in the 1960s, although restrictive contraceptive laws remained in place in many states until the 1965 Supreme Court case Griswald v. Connecticut. Eastern Europe and parts of Scandinavia reformed their abortion laws in the 1960s and England followed in 1967. In 1972 the U.S. Supreme Court struck down state laws forbidding abortion in Roe v. Wade. Advocates for family planning were often led by physicians, such as Alan Guttmacher, president of the Planned Parenthood Federation of the United States, and Fernando Tamayo, leader of Profamilia in Colombia.

In the 1960s, demographers and economists warned of adverse effects of rapid population growth on development. Paul Erhlich captured public attention with The Population Bomb (1968). The Rockefeller and other foundations began to fund family planning. The Swedish government offered international support for family planning, and in the United States General William Draper Jr. persuaded Congress to follow suit.

However, other demographers, such as Kingsley Davis, continued to emphasize socioeconomic development as a prerequisite for smaller families. Gary Becker and others framed decisions about family size as economic decisions based on a rational analysis of costs and benefits of having children. However, given the frequency of human intercourse in relation to conception, the issue is not to decide when to have a child, but how to turn off the possibility of conception, something that can only be done when a couple has ready access to contraception, backed up by safe abortion. Everywhere poor families had more children than rich ones, but the question remained: was this a choice, or did poor people find it more difficult to access contraception and safe abortion?

Those working in the front lines of family planning, led by Reimert T. Ravenholt, the principal administrator in the U.S. Agency for International Development (USAID), believed improving access to fertility-regulating choices was the key to smaller families. He began to implement large-scale programs offering oral contraceptives, IUDs, condoms, and voluntary sterilization as well as initiating surveys of the family planning knowledge, attitudes, and practices of women in developing countries. These surveys have been broadened into Demographic and Health Surveys, and they remain the largest social science surveys ever conducted. Virtually every survey has demonstrated that women are having more children than they intend, and everywhere that realistic family choices were made available, as in South Korea, Thailand, or Mexico, family size fell. Nevertheless, several schools of thought about population continue to compete for intellectual dominance. All are influential in discussions about population, although only those specifically concerned with family planning have put population center stage.


Economists have always played an important, although sometimes contradictory, role in establishing intellectual and public policy related to population. Macroeconomic concerns that the investment required to keep pace with rapid population growth would undermine the economic development of poor countries supported family planning policies in the 1960s and 1970s. In a much-quoted article, “The Tragedy of the Commons,” Garrett Hardin saw rapid population growth exceeding the carrying capacity of the land. But, accepting then-current ideas about the demographic transition, Hardin concluded that voluntary family planning would not ameliorate the threat. Other experts saw the relationship between population and the environment as so complex that they were reluctant to provide clear-cut conclusions. Julian Simon, Ben Wattenberg, and others argued that increasing population would drive technical ingenuity to substitute new materials for declining resources. In the 1980s, the Reagan administration free-market policies trumped any adverse effects of rapid growth. In the 1990s, the pendulum began to swing back when it was shown that countries that had undergone a rapid fall in birth rates had reaped a “demographic dividend” benefiting their economies.

Equity Group

A politically influential group in population research has been those who argue that attention to population takes attention away from the excessive consumption of the first world, reflecting economic inequity, which is the primary injustice needing remedy. This school of thought was influential at the Rio Conference on population and development (Rio de Janeiro, 1992) and in certain circumstances it is a valid conclusion. In other situations, however, there is little doubt that population growth per se is the key factor. For example, in 2000, 179 million people in Egypt, Sudan, and Ethiopia depended on the Nile, which is almost depleted by the time it reaches the Mediterranean. In 2050, 385 million people will compete for the same amount of water.

Women’s Groups

Since the mid-1960s, women’s groups have played an increasingly important role in discussions of population. In Europe and North America, they were forceful advocates for access to family planning as essential to female equality and empowerment. However, a subgroup of feminists opposed hormonal contraceptives as unnatural and feminists in India have prevented the use of the popular injectable contraceptive, DepoProvera, and objected to the use of a low-cost, nonsurgical method of voluntary sterilization.

National Security

Rapid population growth is associated with a high ratio of younger to older men, and analysts in both academia and the U.S. Central Intelligence Agency found a relationship between this ratio and civil disturbances, warfare, and terrorism. It is a theme that was taken up in a secret National Security Study Memorandum requested by President Nixon in 1974, which recommended additional support to international family planning. As can happen in a field permeated with emotions and religious beliefs, and thinking that has no evidential basis, lobbying by Catholic bishops successfully blocked implementation of this memorandum, which was only declassified in 1989.

The Vatican

The Judeo-Christian association of sex with sin goes back to the Adam and Eve myth, but it was St. Augustine’s assertion that coitus can be justified only for procreation that underlies Vatican teaching. In the 1960s, many leading theologians, including the commission the pope himself established, argued that sex had a dual purpose—to express love and to procreate—and that contraception could be used to separate the two. The Catholic physician John Rock, who had played a leading role in developing oral contraceptives, argued in The Time Has Come that the pill was morally acceptable because it imitated the natural suppression of ovulation during pregnancy and lactation. However, Pope Paul IV provided the most wrenching twist in the intellectual history of population of the second half of the twentieth century by reiterating the Augustinian interpretation of sexuality in his 1968 encyclical Humanae vitae. In its wake, priests and communicants left the Catholic Church, and those who remained adopted contraception and safe abortion at the same rate as non-Catholics. While the Holy See continues to oppose family planning on the international stage, Italy voted in two referenda for contraception and safe abortion.

Changing Paradigms and Uncertain Policies

The lack of consensus in intellectual thinking, the strength of faith-based assertions about human reproduction, and competition over limited funds have all fed large and sometimes contradictory swings in domestic and international policies. The first of three landmark decennial international conferences on population in Bucharest in 1974 was summed up by the aphorism that “development is the best contraceptive.” Shortly afterward, however, China instituted a one-child policy and India passed (although it was never implemented) a compulsory sterilization law. By the 1984 conference in Mexico City, the developing countries were asking for mainline family support but the Reagan administration proclaimed that free markets trumped the population explosion.

The 1994 Cairo International Conference on Population and Development (ICPD) saw yet another policy change. Some in the women’s movement began to portray organized family planning as intrinsically coercive and sought to secure the transfer of international resources to broader aspects of women’s health. The ideological shift altered the vocabulary in revealing ways, as gender was substituted for sex and reproductive health replaced family planning. For many, Cairo was an intellectual turning point, but shortfalls in funding have stymied large-scale implementation of the Cairo Program of Action.

The ICPD occurred as the number of AIDS infections was growing exponentially, although calls for action in this area were buried in a plethora of less important issues. In the early twenty-first century AIDS has reached catastrophic levels in some countries, but it will not change the trajectory of global population by much. It has, however, taken priority away from family planning in foreign aid budgets and, as a result, in parts of Africa the trend toward lower birth rates stalled or has been reversed.

In the 1990s, as access to contraception and safe abortion increased in Europe, birth rates fell to below replacement level, while in the rest of the world increases in population fed internal and cross-border migrations, with more and more people crowding into big cities. In 1975, 40 percent of four billion people lived in cities (twenty-six cities had more than five million people); it is estimated that in 2025, of almost eight billion people, 60 percent will live in cities (seventy cities with more five million people). Migration between countries is driven by economic pressures, long exposed borders between high-and low-income regions in North America and Europe, and the relatively low cost of air travel. In Europe, the right of citizens from the British Commonwealth or former French colonies to enter the mother country broke down because of the scale of the populations seeking to migrate. In the United States, policy differences between employers and free-market economists, both endorsing a free flow of labor, and those concerned with the environment remain unresolved.

In the history of ideas about population, abortion has proved the single most divisive topic. Abortion is one way women can limit the number of children they have and an important variable in family size. Globally, it is estimated that, on average, every woman now alive will have one abortion in her reproductive lifetime. Intellectually, the abortion debate has been framed in two ways: either as fetal rights or the mother’s right to control her body—a dichotomy that preempts further debate—or as an ethical question of “when life begins.” The U.S. Supreme Court, however, concluded “that the right of personal privacy includes the abortion decision, but that this right is not unqualified and must be considered against important state interest in regulation.” The abortion debate deeply divides the United States, both because of strongly held religious views and because the Supreme Court, Congress, and state legislators can all set policy. In 1973, Jesse Helms, a conservative U.S. senator from North Carolina, amended the Foreign Assistance Act to exclude any support of abortion, forcing U.S. international family-planning policies into a more conservative mode.

The two most important responses to population growth occurred far outside the Western intellectual tradition. The first was the Chinese one-child policy of 1979, which was driven by intellectual analysis of demographic projections, but the policy encountered much external criticism. Yet, however the policy is viewed, without it, the economic growth in China from the 1990s on could not have happened. The second occurred in the Islamic Republic of Iran, where the average number of children in a family fell from 5.5 in the late 1980s to 2.0, a decline equal to that of China’s, but without a one-child policy. The driving force in the Iranian transition was not socioeconomic change, but a national policy to make all methods of family planning widely available. Iran’s demographers noticed that their population was growing faster than the economy, and if average family size did not decline, poverty would increase. The country’s religious leadership, whose intellectual framework for policymaking in the 1990s was profoundly different from that of Chinese Communism in the 1980s, and totally unlike the Vatican in the 1970s, agreed to family planning if it was for the woman’s health.

On the whole, the intellectual history of population in North America and Europe has been disappointing. There has been increasing methodological sophistication combined with an inability to produce an acceptable paradigm of human reproductive behavior. At the end of the twentieth century, discussion of population growth was pushed off the debating table by competing schools of thought. Yet, serious problems remain. Despite well-publicized declines in birth rates, globally there are one million more births than deaths every 110 hours. India has one million more births than deaths every twenty-three days and China (even with its one-child policy) adds one million people every thirty days.

In the history of ideas, interpretations of population change, appreciation of the consequences, and evidence-based rational responses have a long way to go.