Demographic transition is a model that describes the changes in a population's growth rate over time. It is a theoretical construct that helps to explain the shifts in fertility, mortality, and population growth that have occurred in different parts of the world. The demographic transition model consists of four phases: pre-industrial, transitional, industrial, and post-industrial.
The first phase, pre-industrial, refers to societies that are primarily agricultural and have a high fertility and high mortality rate. In these societies, population growth is slow because the death rate is high, often due to infectious diseases and poor living conditions. However, the fertility rate is also high, as children are seen as a source of labor and support in old age.
The second phase, transitional, is characterized by a decline in both the fertility and mortality rates. This phase is often associated with the Industrial Revolution and the development of modern medicine, which led to improvements in living standards and healthcare. As a result, the death rate starts to decline, while the fertility rate remains high. This leads to rapid population growth, as there are more births than deaths.
The third phase, industrial, is marked by a further decline in the fertility rate and a continued decline in the mortality rate. In these societies, women have more access to education and employment opportunities, which leads to a decrease in fertility. At the same time, advances in medicine and public health continue to drive down the mortality rate. As a result, population growth slows down, although it is still higher than in pre-industrial societies.
The fourth and final phase, post-industrial, is characterized by low fertility and low mortality rates. These societies have reached a demographic equilibrium, with roughly equal numbers of births and deaths. Population growth is slow or even stagnant in these societies.
In summary, the demographic transition model describes the changes in population growth over time as societies move from pre-industrial to post-industrial. It is a useful framework for understanding the shifts in fertility, mortality, and population growth that have occurred in different parts of the world.