Demographic transition refers to a shift in reproductive behavior from a state of high birth and death rates to a state of low birth and death rates. This transition takes place because of advances in agricultural technology and medical science or improvement in hygiene environment, all of which result in corresponding declines in the mortality rate. In this first phase of the demographic transition, population growth rises because the decline in mortality rate has not been coupled with any significant change in parents’ fertility decisions. Then, in the second phase of the transition, parents begin to reduce their fertility as they realize that their ideal number of children can be more easily achieved with fewer births. The widespread use of contraceptive techniques facilitates parents’ attempts to reduce fertility, which in turn causes a decline in the population growth rate. Eventually, the population growth rate converges to a new level, which may be higher or lower than in the pretransitional stage. To facilitate comparison, we can use figure 11.1 to characterize the time and process of the transition. In figure 11.1, Tα marks the apparent starting point of a continuous decline in mortality. Tβ, which normally occurs later than Tα, refers to the time at which the fertility rate begins to decline. Tγ, is the point of lasting return, with an average rate of natural increase equal to or less than that of the period preceding the date of Tα. The convention is to define D = Tγ - Tα as the duration of the transition period. Chesnais (1992) separated the observations of world demographic transition into several types. The first type includes developed countries in Europe and Japan; the second type consists of countries with immigrant European populations, such as the United States, Australia, and Argentina; late-developing countries, such as India. South Korea, and Jamaica, belong to the third type. For countries of the first type, the mortality decline process is closely related to the development of medical technology, which was gradual and spread out over time; hence, the demographic transition is also long. Late-developing countries and those with large immigrant populations were able to adopt the already-developed medical technology from the advanced countries at one time.