Most general theories of population evolved first in ancient Greece. Both policies and their conceptual frameworks varied in details, but there was much consistency from one city-state to another. The typical pronatalist policies were intended not to induce a growth in numbers but to prevent their decline (Stangeland 1904; Hutchinson 1967). In the ideal city-state that Plato (c. 428–348 or 347 B.C.E.) pictured in Laws, the population was to be kept stable at 5,040 (the product of 1 × 2 × 3 × 4 × 5 × 6 × 7) by encouraging or inhibiting fertility or by infanticide. If the population grew much beyond this optimum, the community was to establish colonies. To neglect measures that would keep the population more or less fixed, according to Aristotle (384–322 B.C.E.), would “bring certain poverty on the citizens, and poverty is the cause of sedition and evil” (Politics 2.9).

Greek thought on population, in sum, was characterized by an overriding concern with policy, and thus a relative indifference to empirical or conceptual analysis. Policy was to be applied, moreover, to aggregates ridiculously small by present-day standards. Moreover, the meaning of population was often not in accord with modern senses of the term; in most instances, the term may have referred only to citizens, thus omitting women, children, slaves, and foreigners.

In its far larger arena, Roman policy was more consistently pronatalist. As imperial hegemony spread from Italy throughout the Mediterranean basin and beyond, the center was troubled by moral decay, the dissolution of the family, and a slower growth of population. Successive pronatalist measures culminated in three enactments under Augustus (63 B.C.E.-C.E. 14), which punished celibacy and adultery and rewarded prolific couples (Stangeland 1904). Because they had little apparent effect, the laws were repeatedly amended and finally repealed under Constantine (c. 288–337).

As the Roman Empire gradually disintegrated, many came to believe that the end of the world was imminent, and various sects offered competing dogmas appropriate to the apocalypse. The early Christian church gradually developed its own doctrine with a compromise between libertine and ascetic but emphasizing the latter (Noonan 1965). Catholic thought reached its apogee in the Summa Theologica of Thomas Aquinas (1225–1274). For him, a marriage between Christians is not merely a means of obeying the injunction to replenish the earth but also a spiritual bond, a sacrament. The function of intercourse is procreation (Bourke 1967).

The dominant theme of the early modern period was the view that population growth is precarious and has to be fostered. Just as the mercantilist state hoarded gold, so it hoarded people, and for the same reason—to increase its economic, political, and military power. If rapid population growth resulted in what was termed overcrowding, the mercantilist solution was to ship the surplus to colonies, where the settlers and their progeny could continue to aggrandize the power of the state in another quarter of the globe.

Modern demography began with the efforts of mercantilist states to keep track of their populations (Glass 1973). William Petty (1623–1687) was the first exponent of what he called political arithmetic. John Graunt (1620–1674) constructed the first crude life table. Gregory King (1648–1712) calculated population estimates based on local enumerations, which he corrected for technical errors. On the European continent, Johann Peter Siissmilch (1707–1767) used Protestant parish records to estimate fertility and mortality in Prussia. Richard Cantillon (c. 1680–1734) held that internal migration, deaths, and especially marriages (and therefore births) varied according to the prevailing standard of living and the structure of the demand for labor. François Quesnay (1694–1774) analyzed the implicit bounds to population growth.

The philosophes of eighteenth-century France varied greatly on many issues, but most also found reason to favor policies stimulating population growth. Charles-Louis de Secondat (1689–1755), more commonly known as Baron de Montesquieu, believed that the entire world had undergone depopulation and recommended pronatalist decrees. According to Voltaire (1694–1778), a nation is fortunate if its population increases by as much as 5 percent per century. Louis de Saint-Just (1767–1794) held that one can usually depend on nature “never to have more children than teats,” but to keep the balance in the other direction requires state assistance. By this notion of an equitable family law, as inspired by Jean-Jacques Rousseau (1712–1778), marriages should be encouraged by state loans, and a couple that remained childless after several years ought to be forcibly separated.

The two Utopians whom Thomas Robert Malthus opposed in the first edition of his Essay on the Principle of Page 2411  |  Top of ArticlePopulation, William Godwin (1756–1836) and Marie-Jean Cari tat (1743–1794), known as Nicolas de Condorcet and Marquis de Condorcet, focused their attention on the wholly rational age they discerned just over the horizon. According to them, in a world from which diseases had been wholly eliminated, the span of life would have no assignable upper limit. People would devote themselves to more important tasks than, in Condorcet's words, “the puerile idea of filling the earth with useless and unhappy beings.”

Thomas Robert Malthus (1766–1834) summarized or contravened earlier ideas so effectively that for more than a century and a half, subsequent theorists have generally taken him as a benchmark. Unfortunately, many references to so-called Malthusian thought are based, at best, on the first edition of Essay on the Principle of Population (2008 [1798]) rather than on the much enlarged and thoroughly revised later editions or, at worst, on a total misunderstanding of what Malthus stood for (Petersen 1979).

Malthus was a professor at the newly founded East India College, occupying the first British chair in the new discipline of political economy. He spent much of his life collecting data on the relation between population and its social, economic, and natural environments, bringing his theory into accord with these facts and adjusting it to criticism. There were seven editions of the Essay in all.

According to the principle of population as expounded in the Essay, population when unchecked doubles once every generation. Among “irrational animals” this potential is realized, and its “superabundant effects are repressed afterwards by want of room or nourishment.” But rational human beings can consider the consequences of their reproductive potential and curb their natural drive. With humans, thus, there are two types of control of population growth: preventive checks, the chaste postponement of marriage, and positive checks, the deaths resulting from too large a population relative to its subsistence. Tension between numbers and food can have a beneficial effect: a man who postpones marrying until he is able to support a family is goaded by his sex drive to work hard, thus contributing to social progress. For this reason Malthus opposed contraceptives, for their use permits individual sexual gratification with no procreative benefit to society.

Through the successive editions of the Essay, Malthus increasingly stressed the negative correlation between station in life and size of family. This, in his view, was the principal clue to solving what later became known as the population problem. To bring the lower classes up to the self-control and social responsibility exercised by those with more money and education, Malthus asserted, the poor should be given more money and education. “The principal circumstances” that induce prospective parents to have fewer children are “liberty, security of property, the diffusion of knowledge, and a taste for the comforts of life.” Those that tend to increase procreation are “despotism and ignorance.”

The thesis that upward mobility into higher socioeconomic classes contributes to a decline in the number of offspring produced is far less familiar than Malthus's thesis relating to population growth and access to food, which is in retrospect his most important contribution. For many decades Malthus's reputation was far below that of lesser social analysts. It has become apparent, however, that much of present-day demography was at least partly stimulated by Malthus and that those who denounced him as a false prophet had typically begun by misrepresenting his ideas.

Most of the populations that Malthus discussed tended to grow too rapidly relative to the available resources, and he recommended institutional checks to their fertility. But the extraordinarily rapid growth of the American colonies, whose population was doubling every twenty-five years, Malthus held to be of great benefit. In other words, each country has an optimum size and rate of growth, depending on its social and economic conditions. Malthus neither used the term optimum nor developed the concept beyond an implicit statement, but he planted the seed of the theory.

Malthus's principle that the population tends to increase by a geometrical ratio and food by an arithmetical ratio can be reformulated as a law of diminishing returns. If to a fixed acreage of land more and more labor is added, return per person may first rise but then will decline as the workforce increases beyond its most efficient size. The first definition of the optimum was based on this schema: the optimum is that population which under given conditions produces the highest per capita economic return.

Soon, however, the optimum came to mean simply the best population, with each analyst furnishing a particular evaluative yardstick of what was good. By this route, the theory of population optimum could be regarded as a version of social choice theory with a wide variety of open questions (Dasgupta 1987). Should the population be related to the present institutional structure or to some supposed future (for instance, socialism)? Should the criterion of good be economic welfare, military strength, the conservation of resources, or some combination of these? This conundrum is aggravated by the fact that optima vary greatly, according to the goal that society Page 2412  |  Top of Articlesets. Further, should the standard relate exclusively to the number of people or also to their age structure, rate of growth, level of skill, and other characteristics that affect how efficiently the society can operate?

No judgment concerning the optimum can be precise. Whether a country of western Europe, for example, is underpopulated or overpopulated is less a demographic-economic measurement than a more or less arbitrary opinion. The norm can be applied meaningfully only at the extremes. The colonies that became the United States were definitely underpopulated, as Malthus pointed out. And in some less-developed countries in the early twenty-first century, by the judgment of most demographers, the rapidly growing populations impede a rise in human well-being.

All people are born and all die, but only some move from one place to another. Unlike fertility and mortality, migration is not a biological process. Many determinants of migration are political. Movements are encouraged, subsidized, restricted, or forced, and the status of migrants in their new homeland depends on laws on immigrants and attitudes of the citizenry. If migration is conceived of as following the usual definition—the relatively permanent movement of persons over a significant distance—the specifications permanent and significant must be set by more or less arbitrary criteria. Partly for this reason, migration statistics are generally imprecise and subject to capricious interpretation.

Migration changes the size of populations and the rate of growth in the two areas involved, but usually not in the simple manner that common sense suggests. Most migrants are young adults, and their movement changes the age structure, and thus the birth and death rates, in both areas. Given a sedentary population and a stimulus to emigrate, typically some leave and some do not. There is self-selection by age, sex, family status, and occupation, and possibly by intelligence, mental health, and independence of character. Because migration is not unitary, it cannot be analyzed in supracultural terms but must be differentiated even at the most abstract level with respect to the social conditions obtaining. Generalizations about migration, thus, developed mostly outside standard population theories.

The number of people in the world is increasing at an unprecedented rate to unprecedented totals, and the basic reason is no mystery: mortality has fallen sharply and, in many areas, fertility has not. As originally formulated, and as Adolphe Landry (1874–1956), for example, described in 1934, this so-called demographic transition was conceived as taking place in three broad stages: (1) preindustrial societies, with high fertility more or less balanced by high mortality and a consequent low natural increase; (2) societies in transition, with continuing high fertility but declining mortality and a consequent rapid natural increase; and (3) modern societies, with both fertility and mortality stabilized at low levels and a consequent more or less static population. In its barest form this theory is one of the best-documented generalizations in the social sciences.

Collapsing the whole of human history into these three demographic types means that not only details but also important distinctions are passed over. When actual populations are reconstituted, so simplistic a theory often proves to be less a guide to research or policy than an invitation to misunderstanding. And this has been so concerning each of the three stages (Chesnais 1986).

With respect to the first stage, many scholars assume that the mortality of primitive peoples was high relative to that in advanced societies, but estimates of longevity in ancient times can hardly be precise. Whether preindustrial peoples were warlike, lived in a favorable climate, developed cultural norms promoting cleanliness, and so on certainly influenced their death rates. The usual formula—that because the mortality of primitive humans was high, their fertility must have been close to the physiological maximum if the group was to survive—is also questionable. From an early survey of contemporary primitive cultures, Alexander Carr-Saunders (1922) concluded that all of them included customs intended to restrict the increase of population. There is no reason a priori to postulate that all prehistoric peoples reproduced like unthinking animals, incurring the cost of a subsequent unnecessarily high mortality.

In stage two, the first steps toward a modern industrial society bring about a decline in mortality but also often, contrary to the theory, a rise in fertility. Improved health can result in greater physiological ability to reproduce. Whatever means had been used to reduce population growth, such as infanticide in Tokugawa Japan, may not survive modernization. If the age at marriage had been set well past puberty, as in early modern western Europe, the institutions bolstering this norm often became less effective. Religious practices or taboos unintentionally inhibiting fertility, such as the one prohibiting the remarriage of widows in Hindu India, may dissipate. Most remarkably, family-planning programs can result in a rise in fertility, for if women are able to depend on controls later in their reproductive life, many begin childbearing at an earlier age. In short, the effect of modernization is partly to increase fertility and partly to decrease it (Heer 1966).

In regard to the third stage, the early analysts of the demographic transition failed to forecast the decline of mortality in less-developed countries. Since the early 1800s Page 2413  |  Top of Articleor so, as advances were made in medicine, surgery, sanitation, agriculture, and nutrition, European and North American populations gradually improved in health and longevity. Since the mid-twentieth century, however, newer techniques have been transferred to areas previously lacking most scientific controls. For example, peoples cared for by witch doctors acquired access to antibiotics. In Sri Lanka, to take one striking example, the estimated expectation of life at birth increased from forty-three years in 1946 to fifty-two in 1947. The gain achieved in this one year had taken half a century in most modernized countries.

As a result of the continuing high fertility and the sharp decline of mortality in less-developed countries, populations in those countries have grown at rates high enough to stimulate widespread control measures. Some of these programs have been successful, but many have achieved far less than their proponents hoped they would, in part because none has an appropriate theory underlying it.

Is a large and rapidly growing population a problem? Leaders of the independence movements of pre-1940 European colonies held that poverty in their countries derived not from excessive procreation but from imperial misrule, and this view often persisted after independence. In India the slow start of programs to check population growth, for instance, was due in part to Jawaharlal Nehru's initial ambivalence. Among those who accept the thesis that too many people can impede modernization, proponents have often advocated either birth control or industrialization, as though one or the other were the sole relevant factor.

The theories underlying birth-control programs, often implicit rather than spelled out in papers, reports, and books, can be summed up in the following propositions:

In sum, the many attempts to control fertility and reduce offspring production in less-developed countries have typically been made with little regard to what has been learned from the previous decline in family size in industrialized countries. Perhaps the best link between the two is the wealth-flow theory, so designated by John C. Caldwell (1982). This much cited and often criticized theory maintains that the crucial factor is whether children are productively useful to their parents and care for them in their old age. If so, as in the African cultures Caldwell studied, the incentive is to procreate to the maximum feasible. If, however, parents incur net costs for the long-term care and education of their children, who generally contribute litde to household finances, the inevitable tendency is to reduce the number brought into the world. By concentrating on the family budget, Caldwell was able to elucidate both the historical decline of fertility in industrialized countries and the partial success of family-planning programs in less-developed countries.

A focus on economic or cultural factors can mean that political influences on fertility are bypassed. More generally, theories developed in democratic societies are in many respects ill-suited for analyzing such past totalitarian societies as the Soviet Union and Nazi Germany. Though their cultures differed greatly, these two countries had the following features in common, many of which related to population theory and its application:

The history of population theories reflects that the conception of what constitutes a population and who gets to make such determinations will not only shape its meaning but also have important implications for policy. As Nancy Krieger (2012) argues, although the idea of population is core to population sciences it has rarely been defined except in statistical terms. Krieger traces the idea of populations as technical statistical entities to Adolphe Quételet (1796–1874) and his astronomical metaphor of the average man as a basis for understanding the characteristics and value of a population (Quételet 1835). Although there have been different critiques of this view, it marked a distinctive point of development in thinking about populations and whether one should understand populations as being composed of substantive beings and not merely statistical beings and whether the characteristics of the population were reflections of the innate characteristics of the individuals who composed said populations.

Understanding of populations has become even more complex and nuanced. Much of this contribution was made during the twentieth century with the development of the field of epidemiology and its focus on not merely the characteristics of populations and subpopulations, but also on how causal and structural factors affect the distribution of goods and resources within and across populations, such as health. Krieger (2012, 649) argues for a conception of populations as “first and foremost relational beings, not ‘things’. They are active agents, not simply statistical aggregates characterized by distributions.” With such an understanding, the idea of population is not exclusively a conceptual matter. Understanding populations necessitates a conception that can account for the interactions between the distributions that result from individuals and groups and the social, political, and economic relationships that bind them.

Intellectual history includes few population theories in the narrow sense; most theories were developed as usually minor adjuncts to systematic statements about the society or the economy. Even this thin conceptual framework, however, may have profound ethical implications, for long before anything scientific was known about the determinants and consequences of population growth, statesmen, theologians, and scholars proposed—and their societies sometimes adopted as policies—rules of behavior allegedly suitable to their environment.

Until the modern era, the usual policy orientation was pronatalist, for it was generally assumed both that more people were better than fewer and that realizing faster growth required state aid. Though not the first to take a contrary position, Malthus was by far the most important. Paradoxically, the greatly increased concern with policy in the late twentieth and early twenty-first centuries has not been accompanied by a more precise Page 2415  |  Top of Articledefinition of goals. The judgment of whether a population is too large or too small depends on a reasonably precise designation of the optimum, which has remained perhaps the most controversial concept in demography.

In past times, tyrants and conquering armies slaughtered many aliens, variously defined, but the combination of ruthless nationalism with scientific means of disposing of what were considered inferior sectors of the population was an innovation of the twentieth century. Partly because of a reaction against totalitarian genocide, demographers have given less systematic attention than warranted to such population characteristics as health and skill, though in many contexts these may be more important than mere numbers.

In the late twentieth and early twenty-first centuries the most striking characteristic of population theory and population science has been the attempt to dispense with theory in the solution of population problems widely recognized as critical. The substitution of so-called concern for competence has not led, however, to many successes. In spite of the proliferation of antinatalist programs in less-developed countries and of the numbers of potential parents who accept the contraceptives made available, the world population continues to grow at a rapid rate.

This is a revised version of the entry first written by William Petersen in 1995.