Population Growth and the Demographic Transition Prior to pursuing higher degrees, I was both concerned and fascinated about the world population explosion or population bomb. My naïve assumption was that fertility drove this trend. Exposure to demographic transition “theory,” through graduate studies in demography, led me to realize that it was actually the secular ( long-term) mortality decline which stimulated the explosive population growth. Subsequent studies in epidemiology enabled me to appreciate the overlap between demography and epidemiology, and recognize more fully that Abdel Omran’s Theory of Epidemiologic Transition derives from, and extends demographic transition theory.

Learning Objectives To view population growth from a Malthusian perspective To calculate crude death rates, birth rates, rates of natural increase, and population doubling times To comprehend the concept of the Demographic Transition

Performance Objectives Examine patterns of natural increase Classify populations and sub-populations within the demographic transition framework Predict growth trends in populations and sub-populations

a kindred population science Demography a kindred population science with epidemiology, it shares the Greek root demos (people) and the same founder, 17th century Englishman, John Graunt John Graunt in his Natural and Political Observations…on the Bills of Mortality* detected regularity in patterns of births and deaths. He noticed a higher sex ratio in favor of males at birth and females at age of death. Graunt also constructed a primitive life table (life tables generate life expectancy and survival data) and estimated the population size of London, England. * John Graunt, “Natural and Political Observations Mentioned in a Following Index, and Made upon the Bills of Mortality,” in William Petty, The Economic Writings of Sir W. Petty, vol. 2, ed. C.H. Hull (New York: Augustus M. Kelley, 1964): 314-431.

Demography is the scientific study of the determinants and consequences of human population trends

By the beginning of the 21st century, world population reached 6 billion. Most of the growth has occurred in the past 200 years.

Figure 1 World Population Growth Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 38

The unprecedented population growth of modern times heightens interest in the notion of doubling time. Calculation of population doubling time is facilitated by the Law of 70.

Law of 70 If a population is growing at a constant rate of 1% per year, it can be expected to double approximately every 70 years -- if the rate of growth is 2%, then the expected doubling time is 70/2 or 35 years. More accurately, a population growing at a constant 1% per year would double in 69.3 years. A Law of 70 is much simpler to remember than a Law of 69.3.

T.R. Malthus, 1766-1834 English clergyman, Thomas Robert Malthus, was the first person to draw widespread attention to the two components of natural increase, births and deaths (fertility and mortality).

In his Essay on the Principle of Population, initially published in 1798, Malthus postulated that population tended to grow geometrically (exponentially) while the means of subsistence (food) grew only arithmetically. Malthus is a giant in intellectual history. For example, his thinking strongly influenced Charles Darwin and Alfred Russel Wallace in formulating their respective theories of natural selection. Immensely popular and provocative, the Essay appeared in multiple editions, with the last one being published posthumously. Reference: Thomas R. Malthus. An Essay on the Principle of Population. Text, Sources and Background, Criticism. Editor,Philip Appleman. New York: W.W. Norton, 1976.

The Malthusian Trap arithmetic growth (food): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10… geometric growth (population): 1, 2, 4, 8, 16, 32, 64, 128, 256, 512…

Malthus argued that the difference between geometric and arithmetic growth caused a tension between the growth of population and that of the means of subsistence. -- this gap could not persist indefinitely.

Owing to war, disease, hunger, and vice, mortality would serve as a positive check on population growth.