Population Change. Birth Rates. Death Rates

Population distribution and population densities are subject to considerable variation over time. Where are populations growing most rapidly? Why are population growth rates higher in some areas than in others?

We can compare the population of any place at two given times based on knowledge of four variables. The population will increase by the number born and the number who have moved into the area during the interval between the two times. Over the same interval, the population will decrease by the number who have died or moved away.

In this chapter, we will separate our treatment of migration from analysis of births and deaths. Ignoring migration for the time being, it is clear that population change is dependent on the relative numbers of births and deaths. Population rises in places where births exceed deaths. It remains stable when the number of births equals the number of deaths. When deaths exceed births, the population declines.

Birth Rates. In comparing changes in population distribution, geographers use many different measures to analyze births and deaths. The crude birth rate is the ratio of births to the total population within a given year. Usually, crude birth rates are expressed in terms of the number of live births per 1,000 people. A crude birth rate of 18 per 1,000 implies that 1 8 babies were born in a given year for every 1,000 people already there.

Crude birth rates vary widely throughout the world (Figure 3-4a). The highest birth rates in the world are found in Africa, the Middle East, southern Asia and Latin America. North America, Europe, Japan, and Australia, by contrast, report substantially lower birth rates.

Figure 3-4. Observing Population Differences. Population differences between developed and less developed countries are readily apparent. High rates of fertility (a) and death (b) in the less developed nations are apparent for a variety of economic and cultural reasons. Thus high rates of natural increase (c) result

In various research efforts, human geographers sometimes use alternative measures of birth rates. Agespecific birth rates refer to the number of children born to women in specific age categories. Age-specific birth rates are useful measures of the pace of population growth.

When birth rates among very young women are high, the pace of population growth accelerates more rapidly than when birth rates are higher among older women. The fact that an increasing proportion of women in the developed countries have postponed childbearing until reaching their thirties has helped to slow the rate of population growth in industrial societies.

The total fertility rate, another useful measure of population growth over time, is the average number of children borne by women during their lifetimes. A place with a total fertility rate slightly higher than two has achieved replacement-level fertility. This implies that birth rates and death rates are approximately equal; hence, the population is stable. On the other hand, if the total fertility rate is considerably higher than two, births exceed deaths consistently and the population increases steadily.

Death Rates. Crude death rates are calculated in the same way as crude birth rates. A crude death rate of 14 per 1,000 implies that 14 deaths have occurred for every 1,000 people in a place during a given year. Crude death rates, like crude birth rates, vary throughout the world (Figure 3-4b). Africa and tropical Asia report somewhat higher crude death rates than do Europe and the Americas.

Death rates, like birth rates, can be broken down into age-specific categories. Naturally, age-specific death rates among the elderly are much higher than those among young adults. In addition, death rates are often calculated on the basis of cause of death. Cause-specific death rates illustrate how different causes of death affect age groups differently.

The leading causes of death in the Western world are heart disease and cancer, whose primary victims are the elderly. In years past, however, epidemic diseases like smallpox were among the leading causes of deaths throughout the world. Epidemic diseases strike old and young people indiscriminately. Advances in medical technology have eradicated smallpox and have greatly reduced death tolls from diphtheria, tuberculosis, and other infectious diseases. Because death rates from these causes are now much lower, a higher percentage of the world's population survives to old age.

Age- and cause-specific death rates are useful in calculating life expectancy — the average length of the life span. In the United States and other highly industrialized countries, an infant born this year can expect to live more than 75 years. By contrast, many African and Asian countries report life expectancies of less than 60 years. Differences in life expectancy between developed and less developed countries can in part be accounted for by differences in infant mortality rates — death rates among babies within the first year of life. High infant mortality rates are associated with low life expectancy. They often can be attributed to malnutrition, inadequate prenatal and infant medical care, and the continued prevalence of diseases that affect babies and small children.