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Explain factors that affect total fertility rate in human populations.

Total Fertility Rate

The fertility of a population is the average number of offspring a woman has in her lifetime. For example, some women have 10 children, so they have a higher fertility than women with no children. We often take the average fertility of the population, which allows us to see the average number of children born to each woman.

Explore the graph below. Higher fertility rate indicates a lower median age. Japan’s fertility rate is much lower than Niger’s, so Niger’s median age is 35 years less. Why do you think the Vatican's birth rate is so low?

The total fertility rate of the population is the number of children born to a woman if she were to live to the end of her childbearing years and give birth to children at her country's age-specific fertility rates.

A population with a high total fertility rate will have a lower median age and the base of their population pyramid will be broader.

The graph displays the total fertility rate in various OECD countries from 1970 to 2020. The x-axis spans from 1970 to 2020, and the y-axis ranges from 1 to 3.5, representing the number of children. Each line represents a different OECD country, with colors identified in the legend. Countries exhibit varying fertility rates and degrees of fluctuation. — ***Despite a continued lowering of the global fertility rate, the population is still increasing, why?***

Interestingly, the total fertility rate of most countries has declined in many countries, as seen in the graph to the left. This is due to several factors.

More women are working and completing more years of schooling, which delays and/or reduces childbearing. Globally, we have greater access to contraception, which allows women greater control over their reproductive choices.

Previously, many families had many children to help around the farm and because children were less likely to survive into adulthood. With a population experiencing fewer childhood deaths, and moving away from working on the land, a family no longer needs as many children as possible.

These factors reflect improvements in healthcare, gender equality, and economic development and slow the rapid growth rate of our population. However, it does raise challenges for many developed countries, such as aging populations, shrinking workforces, and more dependence on social security systems. The interactive below discusses some of the factors affecting fertility rates in both developing and developed countries:

We will talk more about developing and developed countries when we talk about the demographic transition later in this module.

Essential Knowledge

Total fertility rate (TFR) is affected by the age at which females have their first child, educational opportunities for females, access to family planning, and government acts and policies.

Replacement Level Fertility

We are also interested in the replacement level fertility. This is how many children parents need to have to replace themselves. At first, you would think this number would be an even two because two parents would need two children to replace themselves. However, because not all children survive into adulthood, the replacement level fertility is actually about 2.1.

The graph depicts global population distribution by fertility levels from 1950 to 2100, showing the cumulative share of the world population on the x-axis and the number of children per woman on the y-axis. Lines represent average fertility rates for different periods, with annotations highlighting specific countries. The trend indicates a shift towards lower fertility rates globally, with most countries projected to have less than 3 children per woman by 2100. — Over time, the fertility of the global human population has decreased. In the 1950s the average TFR was 4.97 children per woman. By the 2090s, the global average TFT is expected to be 1.90, less than the replacement level fertility of 2.1. Yet, the global population still increases, why?

Essential Knowledge

If fertility rate is at replacement levels, a population is considered relatively stable.

Crude Birth Rate

The crude birth rate is the number of live births occurring per 1000 people. This is also known as natality, but we rarely use the term natality. Since the 1950s, the number of live births has been decreasing worldwide. Explore the interactive below to learn more about how global birth rates have changed since 1950:

Crude Death Rate

The crude death rate is the number of deaths per 1000 people. This is also known as mortality and this term is used more frequently. The global death rate has declined across all age cohorts.

The graph displays declining death rates across the lifespan for various birth cohorts in Sweden. The trend reveals decreasing death rates across all age groups over time, with the gap between cohorts widening. Specific data points, like infant, ten-year-old, and fifty-year-old death rates for different birth years, are highlighted. — Death rates have consistently decreased, as we have gained access to better sanitation, clean water, and improved healthcare. Additionally, children are less likely to work in dangerous occupations, such as coal mines or factories.

In general, developing countries will have a high birth rate and death rate, and developed countries will have a low birth rate and death rate.

For example, in 2014, the crude birth rate worldwide was 19.4 and the crude death rate was 7.75. So, the birth rate was more than double the death rate. This helps explain why the human population is growing so quickly.

Essential Knowledge

Factors associated with infant mortality rates include whether mothers have access to good healthcare and nutrition. Changes in these factors can lead to changes in infant mortality rates over time.

Population Momentum

Three line graphs depicting the concept of 'population momentum,' where despite declining fertility rates, high birth numbers persist due to a large number of women in reproductive age. — ***Population momentum causes a population to continue growing even after the births decline.***

But wait, we said birth rates have been declining, so shouldn't the human population decline as well? Not exactly. This is because of something known as population momentum.

Population momentum causes a population to continue growing even after the fertility rate is equal to or less than the replacement level. If a population has many young people, even if the fertility rate is immediately cut, there are still so many people in their reproductive years that the population size still increases.

Current population projections suggest that extreme global population growth will level off around 2100. The question becomes: can our planet support this continued growth through 2100?

AP Exam Tip

You should know the general characteristics of developing vs developed countries and how these characteristics affect the birth and death rates in these countries.

Even though the global human fertility rate has decreased, our population continues to grow because of population momentum.

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