Population growth is linked to overall levels of economic development and that every society follows a typical pattern of development related population growth.
Phase 1: Low population growth in a society because both birth and death rates are very high. This is because the society is underdeveloped and technologically backward.
Phase 2: Low population growth in a developed society where both death and birth rates have been reduced.
Phase 3: This is a transitional stage of movement from backward to an advanced stage which is characterised by very high rates of growth of population.
Population Explosion: This happens 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 behavior to suit the new situation of relative prosperity and longer life-spans.