Industrialization: Demographic Transition Theory
This article is an overview of demographic transition theory. It outlines the differences between the four main stages of the demographic transition and explains what factors help countries move from one stage to the next. It also considers whether some developed nations have moved into a fifth stage of the demographic transition (in which population will decline) and discusses some of the consequences of such a change in terms of the economy and immigration. Population pyramids as a research tool for studying the demographic transition are presented, as is a discussion of trends in global population change. Finally, the article discusses current controversies around the continuing applicability of demographic transition theory to less-developed countries in a time of HIV and other global epidemics as well as continued global population growth.
Demographic transition theory refers to a mathematical model which explains the change in demographic trends as countries move from preindustrial to industrialized economies. The model is based on work observing demographic changes which was begun in 1929 by Warren Thompson, a foundational American demographer. It is important to note that this model is only an idealized picture of how demographic change has occurred; it does not necessarily apply completely to all individual countries. The basic premise of demographic transition theory is that nations go through four stages as they transition from preindustrial to industrialized economies.
The first stage of the demographic transition corresponds to pre-industrialized, or pre-modern, societies. In such societies, both birth and death rates are high. Children are valuable economic actors in society, often performing many household tasks as well as contributing to the agricultural or craft labor that sustains the household. When they reach adulthood, children in premodern societies support their parents, as there is no social safety net and no organized retirement savings. In addition, the lack of medical care and sanitation technology means that disease is rampant and death in childbirth is likely. Famines and epidemics periodically cause marked population declines. Because children are so valuable in premodern societies yet simultaneously so unlikely to survive, people have many children. Yet because of the high death rate, additions to and subtractions from the population tend to even out. In fact, until the Middle Ages, world population growth averaged less than 0.05% a year and it took between one thousand and five thousand years for the population to double.
In the second stage, the population begins to increase at a much faster rate. This is caused by a decline in death rates while birth rates remain high. The decline in death rates occurs for two primary reasons. First of all, improvements in agricultural production, such as those initiated during the Agricultural Revolution in eighteenth century Europe, lead to a more stable and productive food supply. A stable and productive food supply reduces deaths that are a consequence of famine. Second, there are significant advances in public health technology, particularly sanitation, hygiene, and food handling. For instance, cities built sewerage systems that reduced contamination of drinking water supplies and indoor plumbing began to make regular bathing a possibility. Nations that have experienced a demographic transition more recently might also experience improvements in medical care at the same time as improvements in public health technology; in Europe medical care remained quite primitive throughout the second stage of the demographic transition.
During the second stage, the population grows rapidly in a process that demographers call a population explosion. The exact rate of growth varies depending on the society in question, but the growth takes on a common pattern. In particular, the public health advances that are part of the second stage of the demographic transition tend not to increase the lifespan. Instead, they decrease the risk that children will die before they reach adulthood and become able to have their own children. Therefore, more and more people have children, leading not only to an exponential increase in the rate of population growth but also to an age structure in which younger people predominate.
In the third stage of the demographic transition, the population becomes more stable and eventually begins to decline. This decline occurs through the reduction of birth rates, leading to a changed population structure in which there are fewer young people and more old people. However, before the population of old people rises, there is a period of economic opportunity and expansion as more individuals are of working age and fewer are either in childhood or old age.
Demographers and other social scientists debate which factors are most important in producing the changes observed in the third stage. There are five common explanations that are given for the reduction in the birth rate:
- Parents may observe the decline in childhood death rates and determine that they do not need to have as many children as before in order to assure enough household labor and sufficient support in old age.
- Political changes that reduce children's ability to legally earn a wage outside of the home and require parents to pay for clothing and education for their children cause children to be expensive rather than productive members of families.
- When the availability of and knowledge about contraceptive use increase, it gives people the ability to plan childbearing.
- When literacy and employment rates for women rise, women gain more control over their lives and thus their fertility. In addition, women who are working outside the home have less time to raise children.
- Increasing rates of urbanization lead to families who live in smaller spaces and have less need for household labor, increasing the cost and decreasing the utility of extra family members.
The fourth stage of the demographic transition occurs when both birth and death rates are low. In such societies, the population has become quite large, but its size remains stable over time. This occurs when the fertility rate falls below replacement levels, or about 2.1 children per woman. It is important to note that not all societies transition from the third stage to the fourth stage. Nations that are in the fourth stage include the United States, Canada, Australia, most of Europe, several of the more developed nations in Latin America, and the nations of East Asia. Such societies have reaped the benefits of improved agricultural technology, public health measures, and now medical care that allow for massive declines in the death rate, but have not seen corresponding decreases in the birth rate. Such a situation is likely to occur in nations that restrict literacy and employment opportunities for their citizens, especially women; where there are strong religious reasons to continue bearing children at high rates; and where...
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