1. Solution to the Malthusian Trap
Preventive checks: birth control through (1) later age at marriage. (2) abstinence from sex outside marriage.
(Malthus opposed artificial methods of birth control on moral grounds. Viewed contraception as a vice)
The twentieth century witnessed the appearance of neo-Malthusians, many of whom departed from Malthus through advocating the use of artificial methods of birth control (in family planning) to decelerate the growth of burgeoning regional and national populations.

2. Population Explosion
Contrary to Malthus’s prediction, mortality has not yet risen to curb world population growth.
< 1 billion people in 1800
6 billion by the end of the
20th century

3. Population Explosion
Why was Malthus unable to foresee the population explosion (also known as the population bomb)?
He did not recognize the force of the Industrial Revolution, which produced exponential growth in the means of subsistence.

4. The Demographic Transition
During the first half of the 20th century, demographers conceived the notion of the demographic transition.
The Demographic Transition assumes a closed population; that is, a population closed to migration. We can readily conceive the world population as closed, but migration affects population growth of smaller geographic units in varying degrees.

5. The Demographic Transition
The demographic transition framework illustrates population growth in terms of discrepancies and changes in two crude vital rates – mortality and fertility (ignores migration)

6. Crude Death Rate (CDR) = # deaths in calendar year * k
CRUDE VITAL RATES
Crude Death Rate (CDR) =
# deaths in calendar year * k
mid–year population
For demographers, the constant (k) in crude vital rates is usually 1,000; that is, rates are expressed per 1,000 population. Related to greater interest in cause-of-death breakdowns and the smaller numbers implied, epidemiologists differ from demographers in typically expressing crude death rates per 100,000 population.

7. CRUDE VITAL RATES
Crude Birth Rate (CBR) =
# deaths in calendar year * k
mid–year population
Rate of Natural Increase = CBR - CDR

8. Figure 2 The Demographic Transition
The demographic transition is presented as a function of time and socioeconomic development. It traces a change from a state where a population experiences high rates of mortality and fertility, and hence a low rate of natural increase (Stage I), to one where the mortality and fertility rates are low - as is the rate of natural increase (Stage IV). Stages II and III are characterized by high population growth rates due to large discrepancies between respective birth and death rates.
A fluctuating mortality rate in Stage I reflects human helplessness in the face of epidemics, wars and other natural and manmade calamities. The fluctuating fertility rate in Stage IV suggests human decision-making that is sensitive to economic change, and facilitated by modern methods of contraception. Noteworthy, the post-World War 11 baby boom in the United States and other industrialized countries was a mere “boomlet” compared to the population explosion of the demographic transition.
The demographic transition, as theory or concept, cannot be attributable to one person. Rather it reflects the work of a number of scholars including Carlos P. Blacker, Kingsley Davis, Adolphe Landry, Frank Notestein, and Warren Thompson.
Reference:
Dudley Kirk. Demographic Transition Theory. Population Studies 50; 1996:
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 39