The Demographic Transition Theory describes the shift from high birth and death rates to low birth and death rates during a country's development. This theory has four main stages, but this discussion focuses on the first three.
Stage 1: High Stationary Stage
Population remains stable or grows slowly as both birth and death rates are high. High birth rates are driven by a lack of family planning, high infant mortality, and agricultural economies where children are assets. High death rates stem from disease, inadequate medical care, and famine. Pre-industrial societies typically exhibit this stage.
Stage 2: Early Expanding Stage
Death rates decline sharply due to advancements in sanitation, healthcare, and nutrition. Birth rates, however, stay high, resulting in rapid population growth. Countries undergoing initial industrialization, such as those in sub-Saharan Africa, often experience this stage.
Stage 3: Late Expanding Stage
Birth rates begin to fall as a consequence of improved education, family planning, and economic shifts. Individuals opt for fewer children, recognizing the economic advantages of smaller families. More economically developed nations, like Brazil and India, are in this stage.
In summary, demographic transition theory illustrates the progression of societies from high fertility and mortality to low fertility and mortality, linked to economic development and technological advancement.