Trends in Global Population Growth
Today, the world's population is approximately 6.7 billion and increasing rapidly despite a recent decline in overall rates of population growth. Population growth is distinctly uneven worldwide and these differences are reflected in the allocation and use of resources. This article gives a brief overview of population growth processes and surveys recent trends in population statistics, including fertility, contraception, sex ratios, nutrition, HIV/AIDS, urbanization, aging, migration, income distribution, consumption, and biocapacity. Current population trends are indicators of the near future, providing a basis for ongoing attention and research on population issues.
Demographers track several population processes to estimate and project population change. For most of history, and likely pre-history, the world's population change has been marked by high fertility rates, high crude birth rates, high infant mortality rates, high crude death rates, high mortality rates, and low life expectancy. When added together, this means that the world's population turned over rapidly, but absolute numbers grew only slightly or not at all. In demography, a relatively stable condition of no net decrease or increase in numbers is called a population replacement rate.
By 1830, the global population had reached one billion. The second billion in population increase took only 100 years, the third billion about 30 years, the fourth billion 15 years, and the fifth billion only 12 years (Population Reference Bureau, 2007). Figure 1 illustrates this exponential growth of world population since 1950, providing projections through the year 2050 (US Census Bureau, 2011).
By 2013, the world's population had reached approximately 7.1 billion, increasing by around 2.5 individuals per second (US Census Bureau, 2013). Around 1990, we see the beginning of a downward trend in the overall population growth rate. As shown in Figure 2 (US Census Bureau, 2012), if this decreasing trend continues, the rate of population growth will have slowed significantly by 2050.
However, as Figure 1 shows, a decrease in the rate of population growth does not lead to a decrease in overall population. In absolute terms, the global population is projected to increase to over 9 billion people by 2050. According to the Population Reference Bureau, this increase is approximately the size of the combined populations of China and India, the two most populous countries representing two of the highest population growth rates in the world (2007).
Factors Affecting Population Growth
Obviously, genetic, biological, geographical, and ecological factors affect population processes. One of the most well-known theories of population growth was put forth in 1798 by Robert Malthus, who held that world population would grow at a rate just slightly higher than food production. Though "natural" population-limiting processes exist, such as disease, drought, and natural disasters, which tend to increase mortality rates, Malthus predicted a future in which widespread starvation would occur.
Cultural and social factors also have had a tremendous impact on population processes. It is no coincidence that the statistical techniques of demography became more sophisticated around the same time as the term "sociology" was first coined by Auguste Comte. The two fields are complementary to one another, just as social change and population change go hand in hand. For example, the potential of war to dramatically affect population numbers cannot be overstated. If natural conditions produce widespread starvation, social conditions that spur conflict and war can arise.
Demographic Transition Theory
A more recent and even better-known theory of population growth is known as demographic transition theory, which holds that populations move through four distinct stages of growth and decline processes, linked to the technological or developmental state of a given society.
In Table 1, the first stage is representative of most of human history up until the last few centuries. According to demographic transition theory, stages 2 and 3 are periods of expected increases in overall population as societies undergo processes of industrialization and the accompanying changes in food supply, sanitation, medicine, and working conditions. In stage 3, decreasing birth rates and increasing life expectancy begin a period of population decline. In stage 4, the birth rate can either stabilize or decrease. If birth rates are stable, the population again reaches replacement rate.
Table 1: Stages of Population Growth during Demographic Transition
Stage 1 Stage 2 Stage 3 Stage 4 Production Rates (economic goods) Low Increase Increase Stable Fertility Rates High Decrease Decrease Stable Birth Rates High High Decrease Stable Death Rates High Decrease Decrease Stable NET EFFECT: Replacement Growth Declining Replacement
Demographic transition is descriptive of population growth during the era of widespread industrialization. Certainly, global population growth and decline have been geographically uneven, and patterns do differ between more and less industrialized nations, as demonstrated in Figure 3.
Demographic transition theory will be put to the test as India and China, with the world's largest populations, continue to industrialize and we see the outcomes of other recent trends in population processes over the next 40 years.
Recent Trends in Population Processes Fertility & Contraception
Fertility rates in industrialized nations have been declining since the early twentieth century. In many less industrialized countries, the idea of planning and timing children was quite revolutionary. Traditionally, with high rates of infant mortality, larger families held better chances of survival, gaining more status and wealth over time.
During the latter part of the twentieth century, attitudes toward childbearing began to change. The global fertility rates began to decline after 1960, as women in less industrialized countries began to limit the number of their children. Many factors contributed to the changes in fertility patterns in the less industrialized world. Some studies credit organized family planning programs with at least half of that decline (Kent & Haub, 2005).
Growing acceptance of the idea of family planning opened the door to multiple changes in childbearing behavior. In the 1960s and 1970s, surveys to measure knowledge and use of family planning were first conducted in a small number of countries around the world. These surveys found that less than 10 percent of women were using any family planning method. Family planning programs worldwide began to introduce women to more effective pregnancy prevention methods, including female sterilization, intrauterine devices (IUDs), and oral contraceptives. Condom usage, which protects from sexually transmitted diseases (STDs) as well as pregnancy, ranks in popularity below these others in every country; only around 5 percent of women worldwide rely on condoms. Vasectomy, or male sterilization, is used by only about 4 percent of the worldwide population (Kent & Haub, 2005).
By the 1980s, most women were using at least one effective method of contraception, and by 2000, more than half of the world's women of reproductive age were using some method of birth control. In less industrialized nations, the total fertility rate fell from about 6.2 in the 1950s to around 3.0 in 2005. At that time, contraceptive use was higher in some less industrialized countries than in many European countries (Kent & Haub, 2005).
A large body of research over the last several years links higher education for women and girls with reduction in fertility levels. Indeed, recent data from many countries show that women with at least a secondary-level education eventually give birth to onethird to one-half fewer children than do women with no formal education whatsoever. Educated women tend to delay marriage and opt for more control over their reproductive lives (Haub, 2007).
Across countries and time periods, both the sex ratio at birth and the population sex ratio generally varies little between human populations. In 2013, just over half of the human population was male, with males accounted for 50.3% of the global total. In some areas of the world the ratio of males to females is higher, while in other countries, including the United States, females outnumber males. Small variations do occur naturally, but reports began to appear in the 1990s of 100 million or so "missing women" across the developing world (Hesketh & Wei Xing, 2006; Sahni, et al., 2008).
Cultural traditions of preference for sons are seen in almost all patrilineal societies, which link inheritance of property to the males in a family. However, there seems to be some evidence that son preference has distorted expected sex ratios in large parts of Asia and North Africa in particular. The contention is that son preference is now practiced actively in these countries through the increasing availability and use of sex-selective abortion and through discrimination in caregiving practices for girls, which leads to higher female mortality (Hesketh & Wei Xing, 2006; Sahni et al., 2008).
Differential gender mortality in some areas has now been a documented problem for some time. Since the early 1990s, improved health care and conditions for women have resulted in reductions in female mortality, but these advances have now been offset by large numbers of "surplus" males now reaching adulthood. These males are predominantly of low socioeconomic class, and concerns have been expressed that their lack of marriageability and consequent marginalization in society may lead to antisocial behavior and...
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