Natural SelectionEvolutionEvolution 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.AdaptationAdaptations 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.
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