Solution:The demographic transition theory is a generalized description of the changing pattern of mortality, fertility and growth rates as societies move from one demographic regime to another. The term was first coined by the American demographer Frank W. Notestein in the mid-twentieth century, but it has since been elaborated and expanded upon by many others. There are four stages to the classical demographic transition model.Stage I: This stage is particularly seen in least developed countries where birth and death rates are high, due to which the population becomes stable.
Stage II: With the process of development, the birth rate is high, but due to improvements in food supply and sanitation and improved health facilities, the death rate decreases.
Stage III: Birth rate fall but the population increases continuously, because there are a large number of people in the reproductive age group due to the high fertility of earlier generations.
Stage IV: In this stage, both the birth and death rates be. come low and thus population become more stable than the first phase.