Growth of population: four phases

Population growth has two parts: natural growth (births minus deaths) and induced growth (people migrating in or out).

India's growth since 1901 passed through four phases:

• Phase I (1901-1921): stagnant. Both birth and death rates were high, because of famines, epidemics and poor health care. The decade 1911-21 even saw negative growth.
• Phase II (1921-1951): steady growth, as better health and sanitation brought the death rate down.
• Phase III (1951-1981): the population explosion. Death rates fell fast with development and medical care, while birth rates stayed high: growth was about 2.2 per cent a year.
• Phase IV (after 1981): growth is still high but slowing. Birth rates are falling, as people marry later and more girls are educated.

In 2011 the yearly growth rate was 1.64 per cent. Doubling time is the number of years a population takes to double.

In short: deaths fell first; now births are falling too.