Demography studies the quantitative changes in human population, like births, deaths, income, age structure, which inform about the changing structures of human populations and societies. Is the economic system of a country related to the birth and death rates of the country's population? The answer to this question is a certain yes. And that relation is the focus of demographic transition based on the studies, done in 1929, by the American demographer Warren Thompson.
U.S. Post-war Baby BoomThis refers to the period between 1946 and 1964, when there were 76 million births in the United States. Very high fertility rates of more than 3 children per woman reached a peak in the 1950s, when the rate was 3.7 births per woman.
It is a representation of the phases of transition from high birth and death rates to low birth and death rates experienced by a country. It is a model that explains the transformation of a country's population dynamics in progressive stages, corresponding to the economic development of the country. The stages are determined based on the following crucial measures of demography:
Birth rate: Total number of live births per one thousand people in a year.
Death rate: Total number of deaths per one thousand people in a year.
Replacement rate: The extent to which a population is replacing itself. It is the ratio of infant girls to the women of childbearing age.
There are four stages of demographic transition. The transition from one stage to another is different for different regions or countries of the world. The transition is not like a timeline.
Stage I: StationaryBirth rate and death rate, both are high
This refers to human society before the industrial era (before the Industrial Revolution of the 1850s), when humans survived as hunters and gatherers. The availability of food supply determined the number of living population; a drought or famine would result in many deaths (of young and old).
Since both births and deaths almost equaled each other, there was hardly any growth in the population in this pre-industrial society. There was no medical aid like the inventions and discoveries of science we have now, this, coupled with natural calamities, took a huge toll on human life. Also, there were no measures of controlling birth rates, as no contraception was available. In fact, the high death rates led people to have more children (as not all would grow into adults), who could support them in their old age.
This was the condition in almost all parts of the world till the end of the 1700s.
Stage II: Early ExpansionDeath rate drops drastically, but birth rate is high
This stage corresponds to the largest growth of population or population explosion. It marks the beginning of the process of development of a country, seen through increased lifespan of people. The drop in death rates due to improved public health, lesser infant mortality, availability of food, results in population increase. [please note: population does not grow due to the high birth rate]
The agricultural revolution during the 18th century, which brought in systematic cropping patterns and agricultural practices, increased food productivity and yield. Europe witnessed this demographic stage during the 19th century, around the period of Industrial revolution.
On the other hand, the developing countries present a different scenario. They witnessed the second stage in the 20th century (medical advancement in the late 20th century). Also, the overall scientific and technological progress and access to it resulted in a faster drop in the death rates of the developing nations.
Natural Increase: This is the population growth percentage derived from the difference of the death rate and birth rate. This is, thus, the natural increase in the population of a country.
Some developing countries in Sub-Saharan Africa are in this stage.
Stage III: Late ExpansionBirth rate starts to decline and death rate is low
Many reasons like family planning, urbanization, change in economic sectors (with better remuneration or wages), change in the role and status of women (after being literate) in society, medicines assuring longevity of life result in decreased fertility rates, as parents do not fear early deaths of their sons, use of contraceptives (even though limited), change in traditional values or thinking patterns. Decline of birth rates began in the late 19th century in some developed countries of Europe.
Developing and developed countries: Mexico, Brazil, South Africa, China, India are currently experiencing this phase.
Stage IV: Low GrowthBirth rate and death rate both are low
Low birth rates are attributed to the modern lifestyle, individualistic living, easy access to and increased use of contraceptives, nucleated families, realizing the increasing costs and efforts in upbringing of children, etc. Fertility rates begin to show a sharp decline, as women form a significant part of the workforce and are less interested in child rearing. This stage represents a large and stable population. However, there is hardly any growth in population.
Highly developed countries: USA, Europe, Japan, Australia are currently experiencing this phase.
Stage VThe original demographic transition theory proposes only four stages of transition. So, the fifth stage is an addition. It represents a declining trend in population. The death rate falls below the birth rate, leading to population decline or population aging. It is a situation where the population is not stable, like in the fourth stage. The lowering fertility rates reaching below replacement levels in highly developed countries show indications of an aging population.
Germany, Japan and Italy are seen as examples of this stage. Fertility rates are not showing any significant increase here. However, in a few countries like the U.S., the fertility rates bounced back to replacement levels after a decline. So, this stage and its corresponding social indicators are still debated upon.
This model has some limitations also. Not all countries pass through all the four stages in a similar manner. Many developed countries like U.S., Canada, and Australia have not experienced the first stage as they were populated by immigrants. Some African countries have stagnated at the second stage, for lack of industrial development. Such situations are not explained by this model.