(a) Demographic Transition theory is concerned with the historical population growth of a society. It attempts to explain the relationship between fertility and mortality on population growth. The theory explains how all developed countries in contemporary times have passed through three identical stages or population history.
(b) Stages of the theory: Stage (I) (pre-transition phase/stage):
This stage is characterized by high fertility and high mortality rates In this stage the population is fairly stable, static or decreasing or increasing at a low rate.
It is a feature of the pre-industrial society.Stage (II) (Transition stage/phase): In this stage both fertility and mortality are declining. Fertility decline less rapidly at first and then grows more rapidly than mortality leading to an increase tn population. It is a period of population explosion as a result of high birth rates and low death rates.
It is a feature of an economy at the industrial take-off It is feature of developing economy.
Stage (iii) (Post- transition phase/stage):
Both fertility and mortality are low and under control at this stage. The growth rate is controlled as population remains, more or less stable i.e it is a period of low birth rate. and low death rates, which leads to little or no population growth. It is a feature of advanced economy.