History Of Human Population Growth

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From the origin of Homo sapiens, more than 500,000 years ago, until about 10,000-12,000 years ago, the human population grew very slowly. During this time, humans lived in small nomadic groups and obtained food by hunting animals and gathering roots, berries, nuts, shellfish, and fruits. This way of life is called the hunter-gatherer lifestyle. By studying the few hunter-gatherer societies that exist today, scientists have learned that a low rate of population growth results from small populations and high mortality rates. Population growth is slowed especially when mortality is high among infants and young children, because fewer individuals reach reproductive maturity.

The Development of Agriculture

The hunter-gatherer lifestyle began to change about 10,000 to 12,000 years ago, when humans began to domesticate animals and cultivate certain plants for food. This dramatic change in lifestyle is called the agricultural revolution, and it led to profound changes in every aspect of life. Most important, the practice of agriculture greatly stabilized and increased the available food supply. As a result, the human population began to grow faster. About 10,000 years ago, there were between 2 million and 20 million people on Earth. By about 2,000 years ago, the population had increased to between 170 million and 330 million.

The Population Explosion

As you can see in Figure 19-12, human population growth continued through the Middle Ages despite some short-term reversals. The outbreak of bubonic plague in 1347-1352 is thought to have killed about 25 percent of the population of Europe.

Human population growth began to accelerate after 1650, primarily because of a sharp decline in death rates. Reasons for this decline in death rates included better sanitation and hygiene, control of disease, increased availability of food, and improved economic conditions. While death rates fell, birth rates remained high, resulting in rapid population growth. The human population was about 500 million in 1650 and had risen to about 1 billion by 1800 and 2 billion by 1930.

Mortality rates fell sharply again in the decades immediately following World War II because of improvements in health and hygiene in the world's poorer countries. Birth rates in these countries remained high, pushing the per capita growth rate to its highest values. It took most of human history for the human population to reach 1 billion, but the population grew from 3 billion to 5 billion in just the 27 years between 1960 and 1987.

Population Growth Today

The global growth rate peaked in the late 1960s at about 0.021 per capita. Because birth rates have decreased in many countries, the growth rate has gradually declined slowly to its 2004 level of about 0.012 per capita. This decline has led some people to mistakenly conclude that the population is not increasing. In fact, the number of people that will be added to the world population this year is larger than it was when the growth rate was at its peak. This is simply a function of today's greater population size. For example, in 1970 there were about 3.7 billion people, and the growth rate was about 0.0196. In 1970, therefore, about 3,700,000,000 x 0.0196, or about 73 million people, were added to the world's population. In 1999 there were about 6 billion people and the growth rate was 0.014 per capita, so the number of people added to the population was 6,000,000,000 x 0.014, or 84 million.

Today about 20 percent of the world's population live in developed countries. This category includes all of the world's modern, industrialized countries, such as the United States, Japan, Germany, France, the United Kingdom, Australia, Canada, and Russia. On average, people in developed countries are better educated, healthier, and live longer than the rest of the world's population. Population growth rates in developed countries are very low—about 0.003 per capita. The populations of some of these countries, such as Russia, Germany, and Italy, are shrinking because death rates exceed birth rates.

Most people (about 80 percent of the world's population) live in developing countries, a category that includes most countries in Asia, Central America, South America, and Africa. In general, these countries are poorer, and their populations are growing faster—at a rate of about 0.015 per capita.

Human Population Growth Graph

figure 19-12

The J shape of the graph is characteristic of exponential growth. Many ecologists agree that the current human population growth rate is not sustainable.

figure 19-12

The J shape of the graph is characteristic of exponential growth. Many ecologists agree that the current human population growth rate is not sustainable.

Demonstrating Population Doubling

Materials pencil, paper, sheet of newspaper

Procedure

1. Make a data table. Label the columns "Fold number," "Number of layers," and "Power of 2." Write the numbers 1-10 in the first column.

2. Fold a sheet of newspaper repeatedly in half, as your teacher demonstrates. Fill in your data table after each fold.

Analysis If each layer in the paper represented 100 million people and each fold in the paper represented one human generation (about 35 years), how quickly could a starting population of 100 million grow to exceed 6 billion?

Stage 1 Preindustrial

Stage 2 Transitional

Stage 3 Industrial

Stage 4 Postindustrial

High-

Low-

Population size

Death rate

Birth rate

Replacement level birth r /

Time

Large

Small figure 19-13

The demographic transition model consists of four stages. Note the relative changes in birth rates, death rates, and population size.

Word Roots and Origins demographic from the Greek demos, meaning "the people," and graphein, meaning "to write"

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