Demographic transition


Demographic transition is a phenomenon and theory in the social sciences referring to the historical shift from high to low rates of birth and death, as societies attain several attributes: more technology, education, and economic development. The demographic transition has occurred in most of the world over the past two centuries, bringing the unprecedented population growth of the post-Malthusian period, and then reducing birth rates and population growth significantly in all regions of the world. The demographic transition strengthens the economic growth process through three changes: reduced dilution of capital and land stock; increased investment in human capital; and increased size of the labor force relative to the total population, along with a changed distribution of population age. Although this shift has occurred in many industrialized countries, the theory and model are often imprecise when applied to individual countries, because of specific social, political, and economic factors that affect particular populations.
Nevertheless, the existence of some type of demographic transition is widely accepted because of the well-established historical correlation between two factors: dropping fertility rates, and social and economic development. Scholars debate whether industrialization and higher incomes lead to lower population, or vice versa. Scholars also debate to what extent various proposed and sometimes interrelated factors are involved—factors such as higher per capita income, lower mortality, old-age security, and increased demand for human capital. Human capital gradually increased during the second stage of the Industrial Revolution, which coincided with the demographic transition. The increasing role of human capital in the production process led families to invest this capital in children, which may have been the beginning of the demographic transition.

History

This theory is based on an interpretation of demographic history developed in 1930 by the American demographer Warren Thompson. Adolphe Landry of France made similar observations on demographic patterns and population growth potential around 1934. In the 1940s and 1950s, Frank W. Notestein developed a more formal theory of demographic transition. In the 2000s, Oded Galor researched the "various mechanisms that have been proposed as possible triggers for the demographic transition, assessing their empirical validity, and their potential role in the transition from stagnation to growth." In 2011, the unified growth theory was completed, and the demographic transition became an important part of this theory. By 2009, the existence of a negative correlation between fertility and industrial development had become one of the most widely accepted findings in social science.
The Jews of Bohemia and Moravia were among the first populations to experience a demographic transition, during the 18th century, before changes in mortality or fertility with other European Jews or with Christians living in the Czech lands. The demographer John Caldwell explained that fertility rates in the Third World do not depend on the spread of industrialization or even on economic development; he also showed that fertility decline is more likely to precede and facilitate industrialization than to follow it.

Overview

The demographic transition involves four stages, or possibly five.
  1. In Stage 1, that of pre-industrial society, death rates and birth rates are high and roughly in balance. All human populations are believed to have had this balance until the late 18th century, when it ended in Western Europe. In fact, growth rates were less than 0.05% since at least the Agricultural Revolution, more than 10,000 years ago. Population growth is typically very slow during this stage because society is constrained by the available food supply; therefore, unless society develops new technologies to increase food production, any fluctuation in birth rates is soon matched by death rates.
  2. In Stage 2, that of a developing country, death rates quickly drop because of improvements in food supply and sanitation, which increase life expectancy and reduce disease. Improvements specific to food supply typically include selective breeding, in addition to crop rotation and farming techniques. Numerous improvements in public health reduce mortality, especially for children. Before the mid-20th century, these improvements in public health primarily concerned food handling, water supply, sewage, and personal hygiene. An often-cited variable is the increase in female literacy, in combination with public-health education programs that emerged in the late 19th and early 20th centuries. In Europe, the decline in death rates started in the late 18th century in northwestern Europe, and it spread to the south and east over approximately the next 100 years. Without a corresponding fall in birth rates, this change produces an imbalance, and countries in this stage experience a large increase in population.
  3. In Stage 3, birth rates fall because of various fertility factors, such as the following: access to contraception; increases in wages; urbanization; a reduction in subsistence agriculture; an increase in the status and education of women; a reduction in the value of children's work; an increase in parental investment in the education of children; and other social changes. Population growth begins to level off. The birth-rate decline in developed countries started in the late 19th century in Northern Europe. While improvements in contraception play a role in birth-rate decline, contraceptives were not generally available nor widely used in the 19th century. As a result, they probably played an insignificant role in the decline at that time. Birth-rate decline is also caused by a transition in values, not just the availability of contraceptives.
  4. In Stage 4, birth and death rates are both low. Birth rates may drop to well below replacement level, as has happened in countries such as Germany, Italy, and Japan; this drop leads to a shrinking population, which threatens many industries that rely on population growth. As the large group born during Stage 2 ages, an economic burden is placed on the shrinking working population. Death rates may remain consistently low or increase slightly because of increases in lifestyle diseases due to several factors: low exercise levels, high obesity rates, and an ageing population in developed countries. By the late 20th century, birth rates and death rates in developed countries had levelled off at lower rates.
  5. A "Stage 5" is broken out from Stage 4 by some scholars, with below-replacement fertility levels. Other scholars hypothesise a different "Stage 5" involving an increase in fertility.
As with all models, the Demographic Transition Model is an idealised picture of population change in these countries. The model is a generalisation that applies to these countries as a group, and it may not accurately describe each specific case. The extent to which the model applies to less-developed societies remains to be seen. Many countries—such as China, Brazil, and Thailand—have passed through the DTM very quickly because of rapid social and economic change. Some countries, particularly in Africa, appear to be stuck in the second stage because of stagnant development, as well as the effects of insufficient investments and research into tropical diseases such as malaria and AIDS, to some extent.

Stages

Stage 1

In pre-industrial society, death rates and birth rates were both high—fluctuating rapidly according to natural events, such as drought and disease, to produce a relatively constant and young population. Family planning and contraception were virtually nonexistent; therefore, birth rates were essentially limited only by the ability of women to bear children. Emigration depressed death rates in some special cases. But overall, death rates tended to match birth rates, often exceeding 40 per 1000 per year. Children contributed to the household's economy from an early age in multiple ways: carrying water, firewood, and messages; caring for younger siblings; sweeping; washing dishes; preparing food; and working in the fields. Raising a child cost little more than feeding them; there were no education or entertainment expenses. Thus, the total cost of raising children barely exceeded their contribution to the household. Moreover, as children grew into adulthood, they became a major input to the family business, mainly farming; they were also the primary form of insurance for adults in old age. In India, an adult son was frequently the only thing that prevented a widow from falling into destitution. While death rates remained high, there was no question about the need for children, even if a means to prevent their birth had existed.
During this stage, society evolves in accordance with the Malthusian paradigm, with population essentially determined by the food supply. Any fluctuations in food supply—either positive, for example, because of technology improvements, or negative, due to droughts and pest invasions—tend to translate directly into population fluctuations. Famines resulting in significant mortality are frequent. Overall, population dynamics during Stage 1 are comparable to those of animals living in the wild. This is the earlier stage of the demographic transition in the world; it is also characterized by primary activities such as small-scale fishing, farming practices, pastoralism, and small businesses.

Stage 2

This stage leads to a fall in death rates and an increase in population. The changes leading to this stage in Europe were initiated during the Agricultural Revolution of the eighteenth century, and they were initially quite slow. In the twentieth century, the declines in death rates in developing countries tended to be substantially faster. Countries in this stage include Yemen, Afghanistan, Iraq, and much of Sub-Saharan Africa.
The decline in death rates is initially due to two factors:
  1. Improvements in the food supply—brought about by higher yields in agricultural practices and better transportation—reduce death due to starvation and lack of water. Agricultural improvements include crop rotation, selective breeding, and seed drill technology.
  2. Significant improvements in public health reduce mortality, particularly in childhood. These improvements are not primarily medical breakthroughs. For example, Europe passed through Stage 2 before the medical advances of the mid-twentieth century, although there was significant medical progress during the 19th century, such as the development of vaccination. Rather, they are primarily improvements in water supply, sewage, food handling, and general personal hygiene. Hygiene, in particular, improved through growing scientific knowledge about the causes of disease, as well as improved education and social status for mothers.
As a consequence of the decline in mortality during Stage 2, population growth is increasingly rapid, as the gap between death rates and birth rates continually widens. This growth is not due to an increase in fertility but to a decline in deaths. This population change occurred in northwestern Europe during the 19th century because of the Industrial Revolution. During the second half of the twentieth century, less-developed countries entered Stage 2, creating a rapid worldwide increase in population that causes demographers to be concerned today. In this stage of demographic transition, countries are vulnerable to becoming failed states in the absence of progressive governments.
File:Angola population pyramid 2005.svg|right|upright=1.7|thumb| Population pyramid of Angola in 2005
Another characteristic of Stage 2 is a change in the age structure of a population. In Stage 1, the majority of deaths are concentrated in the first 5–10 years of life. For this reason, the decline in death rates in Stage 2 involves the increasing survival of children and a growing overall population. Hence, the age structure of the population becomes increasingly youthful; people begin to have large families, and more of these children enter the reproductive period of their lives while maintaining the high fertility rates of their parents. The bottom of the population pyramid—where infants, children, and teenagers are located—widens first, accelerating population growth rate. The age structure of such a population can be illustrated by using an example from the Third World today.