Human geographers have determined that all nations go through a four-stage process called the demographic transition model (DTM). Developed in 1929 by American demographer Warren Thompson, the DTM’s function is to demonstrate the natural sequence of population change over time, depending on development and modernization. This can help geographers, and other scientists examine the causes and consequences of fertility, mortality, and natural increase rates. Though controversial, the DTM is used as the benchmark for forecasting human population growth regionally and globally.

STAGE 1: LOW GROWTH RATE

We have lived in the first stage of the Demographic Transition Model for most of human existence. In this first stage, CBRs and CDRs fluctuated significantly over time because of living conditions, food output, environmental conditions, war, and disease. However, the natural increase of the world was pretty stable because the CBRs and CDRs were about equal. However, around 8,000 BC, the world’s population began to grow dramatically due to the first agricultural revolution. During this time, humans learn to domesticate plants and animals for personal use and became less reliant on hunting and gathering for sustenance. While this transition allowed for more stable food production and village populations to grow, War and disease prevented population growth from occurring on a global scale.

STAGE 2: HIGH GROWTH RATE

Around the mid-1700s, global populations began to grow ten times faster than in the past for two reasons: The Industrial Revolution and increased wealth. The Industrial Revolution brought with it a variety of technological improvements in agricultural production and food supply. Increased wealth in Europe, and later North America, because of the Industrial Revolution, meant that more money and resources could be devoted to medicine, medical technology, water sanitation, and personal hygiene. Sewer systems installed in cities led to public health improvements. All of this dramatically caused CDRs to drop around the world. At first, CBRs stayed high as CDRs decreased; this caused populations to increase in Europe and North America. Over time, this would change.

Africa, Asia, and Latin America moved into Stage 2 of the demographic transition model 200 years later for different reasons than their European and North American counterparts. The medicine created in Europe and North America was brought into these emerging nations, creating what is now called the medical revolution. This diffusion of medicine in this region caused death rates to drop quickly. While the medical revolution reduced death rates, it did not bring with it the wealth and improved living conditions, and development that the Industrial Revolution created. Global population growth is highest in the regions that are still in Stage 2.

STAGE 3: MODERATE GROWTH RATE

Today, Europe and North America have moved to Stage 3 of the demographic transition model. A nation moves from Stage 2 to Stage 3 when CBRs begin to drop while CDRs simultaneously remain low or even continue to fall. It should be noted that the natural rate of increase in nations within Stage 3 is moderate because CBRs are somewhat higher than CDRs. The United States, Canada, and countries in Europe entered this stage in the early 20th Century. Latin American nations entered this stage later in the century.

Advances in technology and medicine cause a decrease in IMR and overall CDR during Stage 2. Social and economic changes bring about a reduction in CBR during Stage 3. Nations that begin to acquire wealth tend to have fewer children as they move away from rural-based development structures toward urban-based structures because more children survive, and the need for large families for agricultural work decreases. Additionally, women gain more legal rights and chose to enter the workforce, own property, and have fewer children as nations move into Stage 3.

STAGE 4: LOW GROWTH RATE

A nation enters Stage 4 of the demographic transition model when CBRs equal to or become less than CDRs. When CBRs are equal to CDRs, a nation will experience zero population growth (ZPG). It should be noted that sometimes a nation could have a slightly higher CBR, but still experience ZPG. This occurs in many countries where girls do not live as long before they reach their childbearing years due to gender inequality.

When a country enters Stage 4, the population ages, meanwhile fewer children are born. This creates an enormous strain on the social safety net programs of a country as is tries to support older citizens who are no longer working and contributing to the economy. Most of Europe has entered Stage 4. The United States would be approaching this stage if it were not for migration into the country.

A nation in the first two stages of the transition model will have a broad base of young people and a smaller proportion of older people. A country in Stage 4 will have a much smaller base of young people (fewer children), but a much larger population of elderly (decreased CDR).  A nation with a large youth population is more likely to be rural with high birthrates and possibly high death rates. This can tell geographers a lot about the health care system of that nation. Moreover, a country in Stage 4 with a large elderly population will have much fewer young people supporting the economy. These two examples represent the dependency ratio, mentioned earlier in this chapter. This ratio is the number of people, young and old, who are dependent on the working force.

Human geographers like to focus on the following demographic groups: 0-14 years old, 15-64 years old, and 65 and older. Individuals who are 0-14 and over 65 are considered dependents (though this is changing in older generations). One-third of all young people live in emerging nations, and this places considerable strain on those nations’ infrastructure such as schools, hospitals, and day-care. Older individuals in more developed nations (MDL) benefit from health care services, but require more help and resources from the government and economy. The author of this textbook uses the term “emerging nations,” rather than “less developed” or “developing,” or “third-world” nations as a more inclusive and equitable term.

Another ratio geographers look at is the number of males compared to females. This is called the sex ratio. Globally, more males are born than females, but males also have a higher death rate than females. However, understanding a nation’s sex ratio and its dependency ratio helps human geographers analyze fertility rates and natural increase.

As noted earlier, population growth has increased dramatically in the last century. No country is still in Stage 1, and very few have moved into Stage 4. The majority of the world is either in Stage 2 or 3, both having higher crude birth rates than crude death rates; therefore, the world’s population is over 7 billion today.

In summary, the demographic transition model is a model that helps human geographers understand and predict the demographics of individual nations. In Stage 1, CBR and CDR are very high and thus produce a low natural increase. In Stage 2, a nation’s CBR stays relatively high, but the CDR drops dramatically, producing the highest growth in population. In Stage 3, CDR stays low; however, changes in social customs and economic conditions result in a moderately low CBR. Finally, nations in Stage 4 have nearly equal CBR and CDR (sometimes higher CDR), creating a drop in natural increase.