Demography and Population Growth

Learning Outcomes

  • Describe demography and the main demographic measurements used to project population growth
About twenty people on motorcycles and scooters drive along a crowded road with cars and bicycles. Some wear masks and most wear helmets.

Figure 1. At nearly 8 billion, Earth’s population is always on the move, but the methods vary. As you see here, bicycles, motorcycles, and scooters are more common in Vietnam than they are in many U.S. cities. And in some countries, masks were common well before COVID-19. (Credit: Esin Üstün/flickr)

Between 2011 and 2012, we reached a population milestone of 7 billion humans on the earth’s surface. The rapidity with which this happened demonstrated an exponential increase from the time it took to grow from 5 billion to 6 billion people. In short, the planet is filling up. How quickly will we go from 7 billion to 8 billion? How will that population be distributed? Where is population the highest? Where is it slowing down? Where will people live? To explore these questions, we turn to demography, or the study of populations. Three of the most important components that affect the issues above are fertility, mortality, and migration.

The fertility rate of a society is a measure noting the number of children born. The fertility number is generally lower than the fecundity rate, which measures the potential number of children that could be born to women of childbearing age. Sociologists measure fertility using the crude birthrate (the number of live births per 1,000 people per year). Just as fertility measures childbearing, the mortality rate is a measure of the number of people who die. The crude death rate is a number derived from the number of deaths per 1,000 people per year. When analyzed together, fertility and mortality rates help researchers understand the overall growth occurring in a population.

Another key element in studying populations is the movement of people into and out of an area. Migration may take the form of immigration, which describes movement into an area to take up permanent residence, or emigration, which refers to movement out of an area to another place of permanent residence. Migration might be voluntary (as when college students study abroad), involuntary (as when Syrians evacuated war-torn areas), or forced (as when many Native American tribes were removed from the lands they’d lived in for generations).

Mass Migration Crisis

About twenty young people sit on the floor of a holding area with plastic sheeting as walls. Plastic blankets litter the floor, and boxes are outside. In the background a similar holding area with more people can be seen.

Figure 2. This March 2021 image of dozens of children in plastic-lined holding areas was one of a group of photos that sparked public outcry in the early days of the Biden administration, years after similar scenes and situations in the 2014 and 2018 border crises. (Credit: Defense Visual Information Distribution Service)

At least once during each of the last three Presidential administrations, the United States has faced a crisis at its southern border. While images of children in crowded holding areas, covered in piles of shiny plastic emergency blankets, were often associated with the Trump Presidency, Presidents Obama and Biden saw children in the same conditions. The holding facilities, described as cages by some and often referred to as “perreras” (dog kennels) or “hieleras” (ice boxes) by the migrating people, are meant to be temporary stopovers while people await hearings or related refugee processes. But during a number of occasions, the number of people crossing the border was so large – including, at times, tens of thousands of children – that the system became overwhelmed. The conditions are deplorable. The outcomes are uncertain. But the people cross the border anyway.

How did we get here? Bipartisan legislation passed in 2008 guarantees unaccompanied minors a hearing with an immigration judge where they may request asylum based on a “credible” fear of persecution or torture (U.S. Congress 2008). In some cases, these children are looking for relatives and can be placed with family while awaiting a hearing on their immigration status; in other cases, they become involved with the foster system or are placed in of the 170 housing facilities run by nonprofit or for-profit groups. Finally, for people who turn 18 while still in the process, they may be transferred to detention centers, sometimes on their birthday (Montoya-Galvez 2021). Many people in America were either accepting or unaware of these policies and situations until crises occurred in 2014 and 2018-19. At those points of incredible influxes of migrant children, border control, refugee services, and advocacy organizations were overwhelmed by the surge. Both the Obama and Trump administrations pushed for changes in laws or guidelines for enforcement (Gomez 2014 and Kanno-Youngs 2020).

The Obama administration sought to make the decision process faster. In 2014, over 50,000 unaccompanied minors were taken into custody, creating the backlog discussed above. The Trump administration sought to discourage immigration through policies such as separating parents and children who arrived together. The policy was decried by members of Trump’s own party, as well as many other organizations, and was eventually dealt a series of legal blows before the President reversed it. Later investigations determined that hundreds, if not thousands, of children remained separated from their parents for extended periods of time (Spagat 2019).

While the situations at the border are extremely threatening to children’s health and safety, people and policymakers in the United States are divided on how to address the situation. In many cases, these children are fleeing various kinds of violence and extreme poverty. The U.S. government has repeatedly indicated that the best way to avoid these crises is to address those conditions in the migrants’ home countries. But even with financial aid for those nations and pressure on their governments to crack down on illegal activity, it is unlikely that the situation will change quickly or consistently. The Biden administration may not be the last to face a surge of immigrant children at its border.

Population Growth

Changing fertility, mortality, and migration rates make up the total population composition, a snapshot of the demographic profile of a population. This number can be measured for societies, nations, world regions, or other groups. The population composition includes the sex ratio, the number of men for every hundred women, as well as the population pyramid, a picture of population distribution by sex and age.

A population graph shows the percentage of people at each age and by gender. Ages 0 through 4 contains a total of 5.9 percent of the population, with 3 percent male and 2.9 percent female. Ages 20-24 has 6.8 percent of the total population, with 3.7 percent male and 3.5 percent female. Ages 50-54 has 6.4 percent of the population, and it is evenly split between male and female. Ages 70-74 has 4.1 percent of the population and 2.2 percent of that is female. Overall, the graph is relatively even for each age group with a slightly larger group at age 25-29, and beginning to get smaller starting at age 65. Ages older than 65 become progressively lower percentages of the population.

Figure 3. This population pyramid shows the breakdown of the 2019 U.S. population according to age and sex. (Credit:

As the table illustrates, countries vary greatly in fertility rates and mortality rates—the components that make up a population composition. This data is from 2018, and changes occur continually. For example, in 2014, the number of children per adult woman in Afghanistan was 5.4 – generally an average of one more child per family. And the U.S. was slightly higher at 2.0 (World Bank 2019)
Varying Fertility and Mortality Rated by Country
Country Population (in millions) Fertility Rate Mortality Rate Sex Ratio Male to Female
Afghanistan 38 4.4 4.8% 1.05
Finland 5.52 1.4 0.2% 1.04
United States of America 32.8 1.7 0.57% 0.97

Comparing the three countries reveals that there are more men than women in Afghanistan and Finland, whereas the reverse is true in the United States. Afghanistan also has significantly higher fertility and mortality rates than either of the other two countries. In all three cases, the fertility rates have dropped in recent years, but Afghanistan’s drop (from 5.4 children per woman to 4.4) will likely be the most impactful (World Bank 2019). Do these statistics surprise you? How do you think the population makeup affects the political climate and economics of the different countries?

Think It Over

  • Given what we know about population growth, what do you think of China’s policies that limit the number of children a family can have? Do you agree with it? Why, or why not? What other ways might a country of over 1.3 billion people manage its population?
  • Describe the effect of immigration or emigration on your life or in a community you have seen. What are the positive effects? What are the negative effects?
  • What responsibility does the United States have toward underage asylum-seekers?

Try It


the study of population
fecundity rate:
potential number of children that could be born to women of childbearing age
fertility rate:
a measure noting the actual number of children born
mortality rate:
a measure of the number of people in a population who die
population composition:
a snapshot of the demographic profile of a population based on fertility, mortality, and migration rates
population pyramid:
a graphic representation that depicts population distribution according to age and sex
sex ratio:
the ratio of men to women in a given population


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