The theory of demographic transition suggests that population growth is linked to overall levels of economic development. It argues that every society follows a typical pattern of development-related population growth. There are three basic stages of population growth. The first stage is characterized by low population growth in a society that is underdeveloped and technologically backward. In this stage, growth rates are low because both the death rate and the birth rate are very high.

The transition period is associated with a ‘population explosion’ because death rates are brought down relatively quickly through advanced methods of disease control, public health, and better nutrition. However, it takes longer for society to adjust to change and alter its reproductive behaviour to suit the new situation of relative prosperity and longer life spans. This creates a gap where the birth rate remains high while the death rate declines, leading to a population explosion. In India, for instance, the demographic transition is not yet complete as the mortality rate has reduced but the birth rate has not been brought down to the same extent.