The demographic cycle represents the changes in the population of a region as it moves from high births and high deaths to low births and low deaths as that region/society progress from rural, agrarian and illiterate to an urban, industrial and literate society. These changes occur in three stages which are collectively called Demographic Transition Theory. The three stages are:
1. The First Stage: This stage is marked by high fertility and high mortality. The death rate is also high due to epidemics and variable food supply. Therefore, the population growth is slow and life expectancy is low. People are mostly illiterate and engaged in agriculture due to which large families are preferred. Level of technology is also low.
2. Second Stage: In this stage, the expansion of population remains high because the death rate reduces due to the improvement in sanitation and health conditions but the fertility rate remains high. Though at the later stage it declines with time. The mortality rate also decreases. The net addition to a population in this stage is high.
3. Third Stage: In the last stage, both fertility and mortality declines considerably and population either stabilises or grows slowly. The family size is deliberately controlled as the population becomes urbanised and literate. There is a high level of technical know-how in this stage. High technical knowledge contributes deliberately in controlling the family size.