How Natural Selection Affects Populations

Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

Varied genetic traits help species survive changes to their environment. This lesson will explain what happens in a population when one trait is favored over another due to environmental pressures.

Genetic Variation

You may have a different eye color than your best friend or a different hair color than your little sister. If you look at the people you know, it's easy to spot small differences such as these.

Naturally occurring genetic differences in individuals are known as genetic variation. This genetic variation is why you often see different traits such as eye color, hair color, or height, even among close family members. You can observe genetic variation in any species, and in nature it is often key to a population's ability to deal with the unexpected. Let's examine the impact of genetic variation on a population, and the results of this variation in different situations.

Even among family members, genetic variation can express different eye color, height, hair color, or other traits.

Genetic Drift

Sometimes, a change in the variation of genetic traits occurs in a population. These different variations of genes which express different traits are called alleles. Changes in the frequency of alleles are known as genetic drift. When genetic drift occurs, the number of individuals with a certain trait may increase or decrease.

For example, several generations ago, your family had only a few members with red hair. Today, however, this is a trait shared by most family members. In fact, your family is famous for being the red heads in your small town.

Natural Selection

In nature, traits like your family's red hair can have a much greater impact. Individuals that develop beneficial traits have a better chance of survival and individuals with less useful traits are weeded out through the process of natural selection. The greater the variety of traits that exist in a population, the greater the population's chance of survival. This is true because a larger number of alleles provides more options for dealing with changes to the environment.

Imagine beetles living in the flower garden of your front yard. You plant different color flowers in the garden each year and each year, the color of most beetles living in the garden matches the color of the flowers. This is because the beetles that do not blend in with the flowers are more likely to be seen and eaten by predators. The beetles are able to survive the change to flower colors each year because they have a great deal of genetic variability. One of the many different alleles is able to survive each year.

This red ladybug blends in with the color of the red flower. Assuming that yellow and orange variations of the ladybug are also present, the population possesses the ability to blend in with yellow or orange flowers as well.

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