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Demography is the study of the change in the size, density, distribution and composition of human populations over time, and includes analysis of such factors as the rate of birth, death, marriage and fertility, as well as emigration and immigration. The “demographic perspective” is relating population factors (such as the size and growth of a population, or the location in urban and rural areas) to larger political, economic and social issues.

Demography has come to have a wider meaning, and is now used for all statistical descriptions of human life conditions, including illnesses, socioeconomic indicators, and other aspects of living conditions - as long as the statistics refer to the numbers of individual people who exhibit the characteristic in question.

World Population

Table 1: 2005 Population

Name Population 2005 [thousands]
China 1,315,844
India 1,103,371
European Union 476,508
U.S.A. 298,213
Indonesia 222,781
Brazil 186,405
Pakistan 157,935
Russia 143,202
Bangladesh 141,822
Nigeria 131,530
Japan 128,085
Mexico 107,029

Source: UN Population Division. World Population Policies 2005

Demographic history of the world

For more information, see: U.S. Demographic History.

World Population Growth Before 1900

The history of population growth was s-l-o-w growth until quite recently. In the best of times infant mortality and infectious disease caused high mortality; in the worst of times, famine, wars and epidemics wiped out entire groups. The estimated population of the world reached one billion in 1800. In the 19th century change was most dramatic in western Europe and North America. The discovery of the germ theory of disease led to cures or prevention of epidemics. Improved agricultural techniques, plus the opening of new lands in America, increased the quantity and quality of food production. Improved storage, marketing and manufacturing techniques reduced spoilage and wastage. The growth of schooling equipped more people with the intellectual skills needed to take care of themselves. More education meant higher productivity, better food and sanitation, better medical care, less risk taking, smaller families, and an orientation to the future rather than to the past. The "demographic transition" saw death rates fall, and later birth rates fall. In between the two declines, population surged. Growing efficiency of food production lessened the demand for farmers, while the efficiency of factories of new modes of industrial organization (such as corporations) generated higher paying jobs in the cities. As a result, population flowed out of rural areas and into cities. Urban families had fewer children than rural; better educated ones had fewer children. Combined, these factors meant much lower rates of fertility in Western Europe and North America.

Population Growth 1900-1950

The steady decline in infant mortality raised the life expectancy at birth from 45 to 50 years in 1900 to 65 to 70 years by 1950. The rest of the world was in a traditional mode, with high birth rates and high death rates. As public health procedures, education, and better medicines diffused from advanced centers to rural hinterlands and less developed countries, they also experienced the demographic transition. Indeed, there was a speed up in the process. Mexico, for example, underwent its demographic transition much faster than Sweden.

Growth 1950-2000

By 1950 all the industrialized nations had experienced their demographic transition, and in most of them the rural areas had emptied out. Life expectancy continued to rise, now because of new medical treatment for the diseases of old age. The "Reproductive Revolution" began in 1960 with the "pill" and other effective contraceptive techniques, and abortion, and information about family planning. This effectively gave women much more active control over their reproduction. Bangladesh, the poorest of the more populous countries, reduced its fertility rates by half in the last quarter of the 20th century. The sharp decline in childrearing gave countries such as South Korea a one-time "demographic bonus." With fewer children and not yet so many old people, most of the population was of prime working age, thus enabling fast economic growth.

Reversals of Progress

Fertility in poor countries remains twice as high as fertility in developed areas, so the growth of population will continue, and the center of demographic gravity will move toward the poorer Third World. However, so successful have population control policies been in every large country, that when the world population reached the 6 billion mark in late 1999, the fears of the neo-Malthusians were more muted than any time in 200 years. On the other hand, the neo-Malthusians could take gloomy satisfaction from the dismal story of the reversals that took place, notably in Eastern Europe and southern Africa. The collapse of Communism in Russia in the earlu 1990s was accompanied by a deep pessimism about life, characterized by heavy alcoholism, suicide, very low birth rates, soaring death rates, and a six-year decline in life expectancy.

Another reversal came in southern Africa, where the HIV/AIDS epidemic grew increasingly worse. In 2006, worldwide 40 million people were infected with HIV and 2.9 million died. More than 25 million people have died of AIDS since 1981, with the heaviest burden in Africa, where there are 12 million AIDS orphans. Transmission is primarily heterosexual in Africa, and affects younger couples. 11 million children were already orphaned. Drug treatment is vastly more expensive than these poor countries can afford (even after the pharmaceutical giants promised to reduce prices 90 percent). In South Africa the government has taken a radical stand against the use of western therapies and medicines, which have been used elsewhere to prevent pregnant women from infecting their babies. The prognosis is for a rapid decline in life expectancy throughout the southern half of Africa in the early 21st century, from 59 years to 45 years. By 2010 it is estimated that Africa will have 70 million fewer people than otherwise, because of AIDS deaths.

History of the study of demography

The term "demography" was coined in 1855 by a Belgian, Achille Guillard in his book, Elements de statistique humaine ou demographie comparee. In his terms the study included many aspects of humans including general movement and progress (including morals) in civilized countries. He used the vital statistics of birth, marriage, sickness and death from census and registration reports."[1]

Malthus and Malthusian models of overpopulation

see Malthusianism and Malthus

Over the centuries many theorists have considered one or another aspect of population, usually to promote the policy of more people (“pronatalist.”) The early Christian tradition, however, was “antinatalist”, with the highest prestige going to priests, monks and nuns who were celibate.

In the 17th and 18th century the general belief, called "mercantilism" was that the larger the population the better for the nation. Larger population meant more farmers and more food, more people in church (and more prayers), and larger, more powerful armies for deterrence, defense and expansion. People equaled power. As Frederick the Great of Prussia put it, "The number of the people makes the wealth of states." The policy implications were clear: the state should help raise population through annexation of territory and pronatalist subsidies that encourage large families. After 1800, a rising spirit of nationalism called out for more people to make a bigger and more powerful nation.

In 1798 English economist Reverend Robert Malthus in "An Essay on the Principle of Population" turned the received wisdom upside down and decisively restructured the debate. His stunning conclusion was that more people might make it worse for everyone--that overpopulation was bad and unless proper steps were taken, disaster was inevitable. Population growth was exceedingly dangerous, he warned, for it threatened overpopulation and soon we would all starve to death. The British were taking over India at this time, and could see first-hand the horrors associated with overpopulation.

Because of the law of diminishing returns food production can only grow arithmetically: 1, 2, 3, 4, 5, etc. On the other hand, the population next year depends on the population this year, so it always expands exponentially: 2, 4, 8, 16, 32, 64, etc. In other words, population expands faster than the food supply, and eventually people will starve.

Malthus saw two ways to keep population down, "positive" and "preventive" checks. Positive checks were nasty: famine, plague and warfare. Preventive checks included voluntary actions reasonable people could take. Malthus (a clergyman) identified two types of voluntary action, the moral one of deferring marriage, and a variety of "vices" or immoral steps that included birth control, abortion, infanticide, adultery, prostitution and homosexuality.

The Malthus model was unusually powerful: it immediately generated predictions about the fate of mankind. Demography suddenly moved from an abstraction to concrete reality and attracted the attention of scholars and politicians. Economists used the model to show that the more workers there are the lower there wages will be. Charles Darwin made the struggle for food into the centerpiece of his theory of evolution of species.

Two key assumptions Malthus made were that the lure of sex was so strong that people would have babies no matter what the consequences and that technology would grow slowly or not at all. Both assumptions were wrong. Agricultural productivity has increased faster than population growth, and 200 years after Malthus the per capita food consumption in (nearly) all the world is much higher than it was then. The exception in recent decades has been sub-Sahara Africa, where Malthusian predictions of overpopulation and famine have come true.

Regarding Malthus’s first assumption, all societies have created mechanisms to control fertility (for example, by delaying marriage until the couple had enough land to feed themselves.) Everywhere family formation is a social and economic arrangement (not a sexual tryst) and is closely correlated with the supply of land, and jobs. The demographic historian John Hajnal has explored in detail the propensity in Europe in the 18th and 19th century to use delay of marriage as a population control device, tied to the shortage of farmland. In America, with no shortage of good land, the age of marriage plunged to 18 for women and 20 for men by 1800.

There are two schools of thought that follow Malthus. The "Malthusians" and "Neo-Malthusians." Both see overpopulation as a serious threat to mankind, and both agree about the linkage between unrestrained fertility and poverty. The main difference is that the Neo-Malthusians favor birth control as the main solution and the Malthusians want delayed marriage.

Demographics in Medicine and the allied health sciences

see Epidemiology

Demographic analysis is an integral part of epidemiology and in health policy. For example, currently there is a Global Burden of Disease project sponsored by the World Health Organization. (Projections of Global Mortality and Burden of Disease from 2002 to 2030 Mathers CD, Loncar D PLoS Medicine Vol. 3, No. 11, e442 doi:10.1371/journal.pmed.0030442 [1]


See Fertility (demography)


Demographic transition

see Demographic transition

Demographic transition theory was developed by demographers in the 1940s to provide a description and explanation of the main lines of European and American population history.[2] The demographic transition involves three stages:

  • Stage 1: In the first stage, birth rates are high and death rates are high. The population grows slowly.
  • Stage 2: In the second stage modernization begins--especially industrialization (factories and railroads) and urbanization (movement off the farms). Medicine improves, as does personal hygiene and public health. This leads to a sharp fall in the death rate. Everyone lives longer, and infants are much more likely to survive. In the second stage, birth rates remain high so (with fewer deaths) the population increases rapidly.
  • Stage 3: In the third stage, the death rate continues to fall and now the birth rate falls as well. Families become smaller. Instead of the rapid growth of stage two, population growth slows down; indeed, the population may start to shrink.

Policy issues and the future

Old Age issues

Old age is increasingly becoming the number one demographic policy issue in industrialized countries. With fewer and fewer working-age adults, and a fast-growing elderly population that demands more social security payments, medical services, and nursing home care, every major country is faced with the political, economic and social issues of handling this long-term transition. The problem is perhaps least threatening in the United States, where a steady flow of younger immigrants is reducing the aging effect. The problem will be greatest in Japan, Italy and Spain, which are aging very rapidly.


Migration history

The history of migration to US includes the Colonial Era, with largest numbers from England, and others from Scotland, Ireland, Germany, and the Netherlands. The great majority became farmers, in some cases after a few years as an indentured servant. (Young people signed a servitude contract with a ship master who transported them to the American colonies, then sold their contract to a farmer who needed a laborer.) In addition, about 300,000 African slaves were brought in, chiefly from the Caribbean. Flows slacked off between 1776 and the 1840s, then picked up rapidly. The so-called "Old Immigration" saw large numbers arrive, 1840-1880, from Germany, Britain, Ireland, and Scandinavia. Many settled on farms in the Middle West; others worked as laborers and craftsmen in eastern and midwestern cities. After 1890 the inflow became even larger, and originated chiefly in eastern and southern Europe, especially Italians, Poles and Jews. Most of these “new immigrants” worked in low-skill jobs in larger cities, or in coal mines and smaller mill towns. Cultural differences led to fears that society would be drastically changed; hence restrictions and quotas were imposed in the 1920s designed to stabilize the distribution of ethnicity. After 1910, large numbers of Mexicans migrated north to USA. Between 1940 and 1992, 1.2 million Mexicans were admitted with legal documents; another 4.6 million came temporarily as farm workers or "braceros"; and a net figure of around 4 million entered without documents ("illegals"). The status of 2.3 million of the last-named was legalized under a 1986 law. As a result of these migrations and a high birth rate, by 1998 the population of Hispanic origin comprised xx percent of the total US population, two-thirds being from Mexico and the rest from Cuba, Puerto Rico, Dominican Republic, and Central America. In general they hold less-skilled jobs, have low incomes, high dropout rates from school, and high fertility.

Asian immigration to USA came in three phases. From 1850-1880 about 165,000 Chinese arrived, brought in to build railroads; most returned to China, and because few Chinese women arrived, the numbers of Chinese-Americans shrank. In 1900-10, Japanese farm workers arrived in California and Hawaii. Public opinion in the West was quite hostile to the Chinese and Japanese, and numerous laws were passed that tried to stop or slow the inflow. After 1965 racial quotas were ended, and large numbers of Asians began arriving. They included Chinese from the Chinese Diaspora, Koreans, Filipinos, Vietnamese, and Indians, as well as smaller numbers from other lands. The majority settle in California.

Migration policy

Migration continues as a major demographic factor in the 21st century. Travel costs have fallen, education and information levels are higher, and the globalization of the economy means that the world is increasingly a single economic unit. Better educated people in poor countries have a strong incentive to move to high wage countries, which, because of aging, have shortages of skilled labor. In addition, politics and war continues to create refugees who cannot return home. Urbanization has radically changed its tone. A century ago all the world's large cities were centers of business, employment, education and culture--of "urbanity." Now, the largest cities are much bigger and much poorer, as they are crowded with millions of new migrants from the rural hinterlands who eek out a narrow existence. In 2007 half the world's population lives in cities, putting an increasing strain on the infrastructure, the educational system, the economy, and ultimately on the national political structure. A political backlash against immigrants has achieved major proportions in Western Europe and the United States.

Policy: from Politicians or People?

The United States once took a major role in helping poor countries shape population control programs. However, domestic politics has intervened, and at the 1984 International Conference on Population the American delegates announced the "Mexico City Policy," whereby the US would stop funding any agency that promoted abortion. In addition, feminists from North America and Western Europe began to monitor national population control programs, to ensure that women's rights were being protected, and that women were educated and empowered. As more and more private groups entered the arena, it was clear by 2000 that population policy was no longer the preserve of demographers and politicians, but had to be open to the widest possible range of voices.


As countries industrialize and their cities grow, the impact on the environment becomes more severe. Thick brown smog covers much of China and Southeast Asia throughout the year, the product of burning jungles and forests, as well as of new cities, factories and highways that scarcely existed forty years ago. On the optimistic side, city dwellers get much more schooling. The availability of higher education and advanced technical training is much greater in the cities. Some of the graduates will migrate. But others will want to stay close to home, and expect the Internet to bring work to them. Already the Internet is creating high-skilled and high-paying jobs in previously remote areas--all of which are nick-named after California's "Silicon Valley." Thus, "Silicon India" in the Bangalore region now has tens of thousands of software experts, employed long-distance for wages ten times that of their neighbors. "Silicon Bog" employees 50,000 people in Ireland, making that once-bucolic land the number two software center of the world.

Three Scenarios for Century 21

UN demographers work with three scenarios for the next half century, knowing full well how poorly have been predictions made in the past. By 2050 world population will be anywhere from a low of 7.3 billion to a high of 10.7, depending primarily on the change in fertility in poor countries. Countries that in 2000 were more developed had 1.2 billion people in 2000, and will contain from 990 million to 1.4 billion. That is, the range is quite small. (The projections for the USA vary a great deal, depending on assumptions about future migration.) Africa, starting at 780 million, will double or triple--depending, of course, on the what happens to the HIV/AIDS epidemic. Japan and Europe will shrink, and China will either remain steady at 1.3 million or grow slowly to 1.7 million. The rest of Asia and Latin America will grow rapidly.

Table 2: World population in millions, 1950-2050

1950 1960 1970 1980 1990 2000 2005 2015 2025 2050
2,519 3,024 3,697 4,442 5,280 6,086 6,465 7,219 7,905 9,076

Source: UN estimates, 2005

  1. Thomas A Ebert, Oregon State "USA:Demographic Concepts," in Encyclopedia of Life Sciences. 2006
  2. Davis (1945)