The “excess” number of males is the result of sex-selective abortion and female infanticide. Pregnant women sometimes choose to abort after ultrasound examination reveals that the fetus is a female, or less commonly, they kill or abandon newborn girl babies prior to registering their births. The ratio can become more skewed toward males even after birth. A preference for male children means that girls suffer malnutrition more than boys and are given less medical care. This results in higher child death rates for girls than for boys. This imbalance can create social stresses due to a surplus of men unable to marry and form families. In some cases, this leads to human trafficking of women, as male “demand” outstrips female “supply” of spouses. There is also evidence that rates of crime, including rape, are disproportionately committed by unmarried men between the ages of 15 and mid-30s.
Figure 2.28 illustrates how sex selection has become more prevalent in recent decades in three highly skewed countries, China, India, and Azerbaijan. Prior to 1980, the sex ratio at birth in each country was just slightly above the natural rate of 105. However, around the 1980s, the rates rose substantially. This was due to better access to ultrasound technology that allowed the sex of fetuses to be determined. Furthermore, as incomes rose, more families could afford to pay for ultrasound scans. Increased access and affordability of ultrasound scans allowed for greater sex-selective abortion.
Figure 2.28.Sex ratio at birth. Data for China, India, and Azerbaijan show a rapid rise in the sex ratio after the diffusion of ultrasound technology. Data source: United Nations.
In countries with highly skewed sex ratios, cultural norms and laws favor males over females, resulting in a preference for sons. For instance, in India, the families of daughters must pay a dowry when she gets married. In addition, once she is married, she often moves in with her in-laws, caring for them rather than her own parents. Women generally cannot inherit property and are not equal guardians of their children. Furthermore, girls often cannot choose who to marry, and families sometimes feel obliged to commit “honor killings” of their daughters who disobey family wishes. Because of these cultural and legal traditions, parents prefer to have sons.
In some cases, skewed sex ratios come not from a preference for males but from immigration. The most highly skewed sex ratios in 2016 were found in the Middle Eastern countries of Qatar and the United Arab Emirates (figures 2.29 and 2.30). In both cases, the population pyramid shows a dramatic increase in the male population ages approximately 20 to 49, which reflects a large number of male foreign workers in each country.
Figure 2.29.Sex ratio and immigration. Data source: US Census.
Figure 2.30.Foreign construction workers from South Asia in the United Arab Emirates. Photo by Rob Crandall. Stock photo ID: 584348938. Shutterstock.
Go to ArcGIS Online to complete exercise 2.4: “Population structure.”
Population theories
Demographic transition
After observing patterns of fertility and mortality, natural increase, population structure, and more, we want to know why these patterns vary over time and place. The demographic transition model offers a useful explanation by describing how places move through four demographic stages (figure 2.31). In each stage, there are changes in fertility and mortality, which result in differing population growth rates and age structures.
Figure 2.31.The demographic transition model. Image by author.
Stage 1: Preindustrial society
Preindustrial societies are in stage 1 of the demographic transition. From hunter and gatherer societies through agricultural societies, birth rates and death rates tend to be high. Birth rates are high because children are economic assets, helping with hunting, gathering, and farming from an early age. Likewise, children serve as insurance for their parents. They are their “pension plan,” caring for them in their later years, and can also mitigate risk by working for others if output on the family farm is limited. A large number of children are also desirable due to high infant mortality rates. Families must have enough children who survive into adulthood and can, in turn, have their own children and ensure survival of the group. For these reasons, numerous cultures developed that bestow status and prestige on parents with many children and shame those with few children. Gender roles also have a significant impact on birth rates. Stage 1 societies tend to be culturally conservative, where women’s roles are restricted to that of mother and helping with local village tasks. As part of this role, women marry and become mothers at a young age. Given the restricted role that women play in these societies, there is often a preference for sons. Having at least two sons is often the goal of parents to ensure that at least one survives to care for and support the family. Thus, women need, on average, 4.1 children to get two boys. With a reality of high infant mortality rates, an even larger number of births is often required.
Death rates also tend to be high in stage 1 societies due to disease and unstable food supplies. A lack of proper nutrition, along with limited calorie intake in hard times, results in many deaths, especially among infants and young children. At the same time, communicable diseases kill many children due to a lack of medical knowledge. Diseases that are spread by other humans, animals and insects, and unsanitary water—such as influenza, cholera, malaria, and plague—ensure that death rates remain high.
In stage 1, population growth (natural increase) remains flat, or close to zero, given that both birth rates and death rates are high. This was the situation for most of human history.
Stage 2: Early urban-industrial societies
Societies enter stage 2 as they begin to industrialize and urbanize. In this stage, birth rates remain high, but death rates begin to fall substantially for several reasons. With industrial and urban development, agricultural technology leads to more stable food supplies and thus better nutrition and calorie intake. Furthermore, knowledge about germs improves, and the development of public health programs expands. Clean water and sewer systems are gradually built, which reduces waterborne disease. Meanwhile, rodent and insect controls are put in place, and the use of soaps and disinfectants is promoted. In addition, medical technology improves and accessibility diffuses to a larger proportion of the population.
For instance, the smallpox vaccine was widely used by the early 1800s, resulting in many fewer deaths from that deadly disease. Also in the 1800s, English physician John Snow linked a water well to an outbreak of cholera, using spatial analysis to show that the disease was waterborne and not airborne (figure 2.32). His discovery contributed to the eventual development of urban water and sewer infrastructure.
However, during stage 2, birth rates remain high as people maintain the cultural tradition of having large families both in rural areas and in expanding urban areas. Cultural traditions that limit the role of women and esteem large families and deride small ones still influence family size. Furthermore, a preference for sons pushes parents to keep having children until at least two boys are born.
With a large difference between births and deaths, natural increase rises and population growth increases significantly in this stage.