Natural Selection

Natural Selection - Natural Selection Evolution Evolution...

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Natural Selection Evolution Evolution refers a change in the gene frequency of a population. For example, suppose that in a certain human population in 1990, 65% of the eye color genes were for blue eyes and 35% were for brown eyes. In 2000, the number of blue eye genes was 67%. This small evolutionary change may not be noticeable, but over time, small differences accumulate to produce larger differences. A number of natural phenomena can act to change gene frequencies. Organisms moving into or out of a population (migration) can cause gene frequencies to change. Random fluctuations can also cause changes, particularly in small populations. Natural selection (described below) is particularly important in causing changes in gene frequencies. Adaptation Adaptations are structures or behaviors that allow efficient use of the environment. For example, the webbed foot of a duck enables it to swim better than a foot that is not webbed. Adaptations are due to genes , that is, they are inherited. Natural Selection As was noted in the introductory paragraph above, natural selection is one of several different mechanisms that cause evolutionary change in populations. Natural selection operates to produce individuals that are better adapted to their environment. It is important to keep in mind as you read below that natural selection does not act on individuals; it acts on populations. Individual organisms cannot become better-adapted to their environment because they cannot change their genes. Natural selection produces changes in the genetic composition of a population from one generation to the next. As a result, organisms become better adapted to their environment. Natural selection occurs because 1. Individuals within a population vary; they are not all identical. 2. Some variants are “better” than others. As a result, they have more reproductive success. 3. The traits that vary are heritable. If the above three items are true, then the “better” individuals will have more success
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This note was uploaded on 07/20/2011 for the course BIO 101 taught by Professor Krm during the Summer '11 term at LSU.

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Natural Selection - Natural Selection Evolution Evolution...

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