1. Chapter 2 Key Issue 4 Why Might the World Face an Overpopulation Problem?

2. Malthus on Overpopulation • One of the most famous models to explain changes in population over time was developed by Thomas Malthus. Malthus was an English economist and demographer who published his Essay on the Principle of Population in 1798. • He argued that the world’s population was growing geometrically or exponentially but food supplies were only growing arithmetically. • According to Malthus this would lead to “negative checks” consisting of starvation and disease because of lack of food. The only way to avoid this would be for populations to lower crude birthrates.

3. Neo-Malthusians • Malthus’ theory is still potentially relevant today because of rapid growth in some LDCs. His adherents today are called neo-Malthusians and are led by Paul Ehrlich, who has made a similar argument to Malthus in The Population Bomb. • Neo-Malthusians such as Robert Kaplan and Thomas Fraser Homer-Dixon have broadened Malthus’ theory to include fuel, agricultural land, and other resources as well as food.

4. Malthus’s Critics • Malthus has critics, too. The Marxist theorist Friedrich Engels believes that the world has enough resources to eliminate hunger and poverty if they are more equally shared. • Contemporary critics include Julian Simon and Esther Boserup, who argue that larger populations can actually stimulate economic growth. • Malthus was terribly pessimistic and did not foresee the development of new agricultural technologies or the human ability to reduce population growth rates.

5. Declining Birth Rates • Most demographers would agree that some parts of the world are overpopulated, a condition in which a country can no longer sustainably support its population because it has reached its carrying capacity. • In human geography the carrying capacity refers to the number of people a given area can support. • The CBR has declined rapidly since 1990 except in some countries in Sub-Saharan Africa. This has occurred partly as a result of economic development, which has resulted in more money for education and health care. • Birthrates have also lowered because of diffusion of modern contraceptives. Some countries, such as Bangladesh, have reduced their birthrates like this without economic development. There is opposition to birth-control programs from some countries for religious and political reasons.

6. World Health Threats • Medical researchers have identified an epidemiologic transition that focuses on the causes of death in each stage of the demographic transition. Epidemiology is the branch of medicine which is concerned with disease.

7. Epidemiologic Transition Stages 1 & 2 • In stage one of the epidemiologic transition, infectious and parasitic diseases were the main causes of death. • These include the Black Plague and cholera pandemics. • A pandemic occurs over a wide geographic area, unlike an epidemic, which is more localized. These causes of death were most common for people in countries in stage 1 and the early part of stage 2 of the demographic transition.

9. Stage 3 & Stage 4 of the Epidemiologic Transition • Stage 3 of the epidemiologic transition is associated with degenerative and human-created diseases such as heart diseases and cancer. • As LDCs have moved from stage two to stage three of the demographic transition, the incidence of infectious diseases has declined. • Human -created diseases are more typical of countries in stage four of the demographic transition.

10. Stage 5 of the Epidemiologic Transition • Some medical researchers have argued that the world is now moving into stage five of the epidemiologic transition, characterized by a reemergence of infectious and parasitic diseases. • This could be for a number of reasons, including the evolution of infectious disease microbes, poverty, and improved travel. • Avian flu is one of the “new” infectious diseases that has emerged in recent decades, and it has the potential to become pandemic. • However, AIDS is the most lethal epidemic of recent years, especially in Sub-Saharan Africa, where more than 25 million people were infected with HIV in 2005.