Demographic transition
In demography, the term demographic transition is used to describe the transition from high birth rates and death rates to low birth and death rates that occurs as part of the economic development of a country from a preindustrial to a postindustrial economy. Usually it is described through the "Demographic Transition Model" that describes the population changes over time. It is based on an interpretation begun in 1929 by the American demographer Warren Thompson of the observed changes, or transitions, in birth and death rates in industrialized societies over the past two hundred years or so. Most developed countries are already in stage four of the model, while many developing countries are in stages one and two.
DTM Summary
The transition involves 4 stages.
- In stage one, a preindustrial society, death rates and birth rates are both high and oscillate according to natural events such as drought and disease to produce a relatively constant and young population.
- In stage two, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease. These changes usually come about due to improvements in farming techniques, access to technology, basic healthcare and education. Without a corresponding fall in birth rates this produces an imbalance, and the countries in this stage experience a large increase in population.
- In stage three birth rates fall due to access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, the increase in the standing and education of women and other social changes. Population increase begins to level off.
- During stage four there are both low birth rates and death rates. Birth rates may drop to well below replacement level as has happened in countries like Italy, Spain and Japan, leading to a shrinking population, a threat to the many industries that rely on population growth. The large group born during stage two ages, creating an economic burden on the shrinking working population. Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high obesity and an aging population in developed countries.
As with all models, this is an idealized composite picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. The extent to which it applies to less-developed societies today remains to be seen. Many countries such as South Korea, China, Brazil and India have passed through the DTM very quickly due to fast social and economic change. Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS.
Stage two in detail
This stage leads to an increase in population and rapid fall in birth rates. The changes leading to this stage in Europe were begun in the Agricultural Revolution of the 18th century. Countries in this stage include Nigeria, Kenya and Bangladesh. The decline in the death rate is due initially to two factors:
- First, improvements in food supply brought about by higher yields as agricultural practices. These improvements included crop rotation, selective breeding, and seed drill technology. In England, the greater wealth this brought about enabled people to work less on farms, marry earlier and so contributed to industrial development and raised the birth rate slightly at the same time. Another food-related factor was the introduction of potato and maize (corn) from the Americas. These new crops increased the quantity of foodstuffs in the European diet, especially in northern Europe. In developing countries today the changes are due to increases in agricultural yields due to the use of high yielding varieties and other improvements in farming technique typical of the green revolution. Increased knowledge of basic nutrition and access to protein and vitamins and minerals in a more varied diet also improve health in countries with malnutrition.
- Second, significant improvements in public health reduce mortality, particularly in childhood. These are not so much medical breakthroughs (Europe passed through stage two before the advances of the mid-20th century) as they are improvements in water supply, sewage, food handling, and general personal hygiene following on from growing scientific knowledge of the causes of disease. This is illustrated below for the case of measles and TB in the USA over the past 100 years. However, bear in mind that killer infectious diseases such as TB are airborne and not water borne, so public engineering works such as sewer and water supply cannot take all the credit. In fact, perhaps the most important factor here was increased female literacy allied with public health education programs in the late 19th and early 20th centuries. In developing countries today access to contraceptives to prevent AIDS, vaccinations and access to antibiotics are also important factors.
A consequence of the decline in mortality in Stage Two is an increasingly rapid rise in population growth (a "population explosion") as the gap between deaths and births grows wider. Note that this growth is not due to an increase in fertility (or birth rates) but to a decline in deaths. This change in population occurred in northwestern Europe during the 19th century due to the Industrial Revolution. During the second half of the 20th century less-developed countries entered stage two creating the worldwide population explosion that has demographers concerned today.
Another characteristic of stage two of the demographic transition is a change in the age structure of the population. In stage one the majority of death is concentrated in the first 5–10 years of life. Therefore, more than anything else, the decline in death rates in Stage Two entails the increasing survival of children. Hence, the age structure of the population becomes increasingly youthful. This trend is intensified as these increasing numbers of children enter into reproduction while maintaining the high fertility rate of their parents. The age structure of such a population is illustrated below by using an example from the Third World today:
Stage three in detail
Stage three moves the population towards stability through a decline in the birth rate. In general the decline in birth rates in developed countries began towards the end of the 19th century in northern Europe and followed the decline in death rates by several decades. Many countries are currently in this stage including India, Mexico and Brazil. There are several factors contributing to this eventual decline, although some of them remain speculative:
- In rural areas continued decline in childhood death means that at some point parents realize they need not require so many children to be born to ensure a comfortable old age. As childhood death continues to fall and incomes increase parents can become increasingly confident that fewer children will suffice to help in family business and care for them in old age.
- Increasing urbanization changes the traditional values placed upon fertility and the value of children in rural society. Urban living also raises the cost of dependent children to a nuclear family (education acts and child labor acts increase dependency). Partly due to education and access to family planning, people begin to assess more rationally just how many children they desire or need. Once traditional patterns of thinking are broken the decline is likely to accelerate. People in urban areas often become more materialistic and seek a better quality of life rather than large families.
- Increasing female literacy and employment lower the uncritical acceptance of childbearing and motherhood as measures of the status of women. Valuation of women beyond childbearing and motherhood becomes important. In addition, as women enter the workforce their life extends beyond the family, and the connections they make with other women serve to break their isolation and change their attitudes towards the burdens of childbearing. Within the family they become increasingly influential in childbearing decisions.
- Improvements in contraceptive technology are now a major factor, but contraceptives were not widely available in the 19th century and so did not contribute to the European decline. Fertility decline is caused as much by changes in values about children and sex as by the availability of contraceptives and knowledge of how to use them. Today in the world there exists a close correspondence between fertility and contraceptive use, but this likely means that those families that have chosen to limit family size find contraceptives the easiest and most effective way to do so. In some countries birth rates fall more slowly or not at all because traditional religious beliefs inhibit the use of contraception.
The resulting changes in the age structure of the population include a rapidly aging population, a sharp decrease in the number of young people, reducing the youth dependency ratio. The population structure becomes less triangular and more like an elongated balloon.
Source
Keith Montgomery has given permission for the contents of this page to be moved into Wikipedia.