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The Human Population: Factors that Affect Population Size

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  • 0:05 The Human Population
  • 1:51 Factors That Increase…
  • 4:05 Factors That Decrease…
  • 5:47 The Population Growth Rate
  • 6:35 Lesson Summary
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Lesson Transcript
Instructor: Margaret Cunningham

Margaret has taught many Biology and Environmental Science courses and has Master's degrees in Environmental Science and Education.

The human population is constantly changing. In this lesson, we will explore the factors that cause increases and decreases in the human population, including births, deaths, immigration, and emigration.

The Human Population

Take a minute and think about all of the different people you interact with in a given day. For most people, this would include family, friends, co-workers, and strangers. A population is often described as a group of individuals of the same species that inhabit the same area. Therefore, all of the people you encounter each day are part of your population. Other examples of populations include the dandelion plants growing in a field or the cockroaches that inhabit a single house.

On a larger scale, you can think of all humans on Earth as the human population. As of 2011, the human population exceeded seven billion people! Although the human population has been around this size for most of us for our entire lives, the population has not always been so large.

Around 10,000 years ago, before the invention of agriculture, it is estimated that the human population was only a few million people worldwide. After the invention of agriculture, the human population began to grow slowly until the 1900s, when a rapid increase in the human population began. With increases in technology and medical advances, the human population was able to reach three billion in the 1960s. Since that time, the population has more than doubled and continues to increase.

Now that we know how the human population has changed overtime, it is important to investigate the factors that have influenced these changes. There are many factors that can influence the size of a population. Some factors result in an increase in the population, while others can cause a decrease in population size.

Factors that Increase Population Size

There are two factors that result in an increase in the size of a population. First, there is natality, which is the number of individuals that are added to a population over a period of time due to reproduction. This term is often used to describe reproductive rates over a variety of time periods.

The term most commonly used when describing natality in the human population is 'birth rate'. Birth rate is the number of individuals born per 1,000 individuals per year. An example of birth rate would be if a population of 5,000 people resulted in the birth of 50 children in a year, which would yield a birth rate of ten individuals per 1,000 per year. Birth rate is often reported as a percentage of the population. In 2010, the birth rate in the United States was 1.38%, which is considerably lower than the birth rate in many developing countries. For example, in 2010, the birth rate in Ethiopia was 4.34%. Birth rates can vary a great deal by region and can have drastic effects on the overall human population.

The second factor that can cause a rise in a population is immigration. Immigration is the migration of an individual into a place. When an individual immigrates to a new location, they increase the population within that area. Immigration is a factor that can influence the size of a specific population of humans, but does not influence the overall human population.

For example, if an individual decides to move from London to New York, they would be immigrating to the United States and would therefore increase the population of the U.S. Their immigration would have no influence on the overall human population because no matter where they live, they are included in the size of the human population. The only way that immigration could influence the overall human population on Earth is if humans lived on a different planet and immigrated to Earth. In that scenario, the human population on Earth would increase.

Factors that Decrease Population Size

Now that we have learned about the factors that increase population size, let's investigate the factors that have the opposite influence. The first factor that results in a decrease in the population size is mortality. Mortality is the number of individual deaths in a population over a period of time. In terms of the human population, mortality is often described as the death rate, which is the number of individuals that die per 1,000 individuals per year.

Death rates are often used to describe how many individuals die in specific age groups. For example, the death rate of infants is often an important statistic to investigate when looking at changes in the population. Similar to birth rates, the death rate is also often described as a percentage of the population. In 2010, the death rate for infants in the United States was 0.6%, while in Ethiopia the infant death rate was 7.1%.

The second factor that can decrease the size of a population is emigration. Emigration is the migration of an individual from a place. When an individual emigrates from a location, they decrease the population within that area. If you think back on the immigration example, with the person moving from London to New York, we said that the person was immigrating to the United States. Using this same example, the person would also be emigrating from England. Similar to immigration, emigration also does not have an influence on the overall human population on Earth because people are not leaving Earth to move to a new planet.

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