Perspectives on the Problem of World Population Growth

The Malthusian Dilemma. The most famous and perhaps most influential model of world population growth was proposed by Thomas Malthus, an English clergyman, over two centuries ago. Malthus argued that human populations grow geometrically or exponentially--that is, by doubling every few generations, as in the series 2-4-8-16. In contrast, he contended that food resources could only increase arithmetically or in additive increments, such as 4-5-6-7. As shown in the following diagram, Malthus believed that, at these differing rates of growth, a population would eventually outstrip its supply of food. At that point, positive checks on population growth--famine, disease, and war--would come into play and bring the population back into balance with its food resources.

The Population Growth Equation. The field of demography deals with the growth and composition of human populations. Demographers basically deal with three variables that affect population change: (B) the fertility or birth rate; (D) the mortality or death rate; and (M) the net migration rate. As depicted in the following equation, which is typically referred to as the population growth (or balancing) equation, the rate of change (delta) in a given population (P), is a function of these three variables.

The Demographic Transition Model. Kingsley Davis, a well-known demographer, formulated a relatively simple model that describes different historical stages in the growth of populations. Davis originally applied this model to changes that occurred in Western European populations over the course of several centuries, beginning with the pre-industrial Middle Ages and ending with the industrialized 20th Century. However, the model is also useful for describing the current problem of rapid population growth in developing nations, which have experienced a dramatic decline in death rates while birth rates have remained relatively high. As shown in Stage 2 below, the shape decline in death rates in developing nations after World War II has resulted in a high rate of natural increase in their populations. Some nations in Asia and Latin America appear to be entering Stage 3, but the gap between birth rates and death rates remains large in many regions of the Third World.

Population Pyramids.