The Demographic Transition

In one line

Every society that has developed has moved from high birth rates and high death rates to low birth rates and low death rates, and the population explosion is what happens in the middle.

In the wording a student can write in an exam: the demographic transition is the historically observed movement of a society from a regime of high birth rates and high death rates, through a phase in which death rates fall while birth rates remain high, to a regime of low birth rates and low death rates. Population grows rapidly only in the middle phase, and the transition is completed when fertility approaches replacement level.

The four stages

Stage one: high stationary. High birth rates and high death rates, both fluctuating with harvest and epidemic. Population is large in its churn and small in its net change, and this is the position of most of human history.

Stage two: early expanding. Death rates fall, principally among infants and children, because of public health, nutrition, clean water and the control of epidemic disease. Birth rates remain high, because the reasons for having many children, being the survival of some of them, labour, and security in old age, have not yet changed. The gap widens and population grows very fast. This is the explosion.

Stage three: late expanding. Birth rates begin to fall, because children now survive, because they cost more and earn later in a wage economy, because girls are educated and marry later, and because contraception is available. Growth continues but at a declining rate.

Stage four: low stationary. Both rates are low. Population is roughly stable, and its age structure is much older.

And a fifth stage is sometimes added, in which fertility falls below replacement and population declines, which is the position of several countries in Europe and East Asia.

Where India is

India entered stage two after 1921 and was in it through the explosion of 1951 to 1981. It entered stage three as fertility began to fall, and it is now at the end of stage three or the beginning of stage four, with fertility at about replacement level nationally.

But the transition is uneven within India, and this is the point that makes the model useful rather than decorative. Several States, particularly in the south, completed the transition decades ago and have been at or below replacement fertility for a long time. Several northern and central States entered stage three later and are still in it.

Two consequences for a legal answer. A national population policy addresses a country in which different States are at different stages, so the same instrument means different things in each. And the environmental pressure of population growth is now regionally concentrated, which is an argument for regional rather than national measures.