What Is Meant by Fitness

The phrase "survival of the fittest" may conjure up an image of a big strong lion with his pride of lionesses producing many lion cubs. In that example, the genes of the strong lion, as well as those of the lionesses he chooses, will have a greater chance of being passed down to future generations of lions than the genes of a weak lion without any lionesses. We say that the genes of the strong lion are "selected" because of his ability to father more lion cubs. This, however, is not the only type of selection that exists in nature. Indeed, in the example of a field of four -o'clock plants in chapter 10, we saw a different type of selection. In that case, the preference of insect pollinators could increase the chances of one color gene being favored over another. Thus, selection is a process in which the individuals considered the

"fittest" are those that have a higher chance of passing on their genes to the next generation. There are many ways to achieve this. To put it differently, the term "fitness" in this genetic sense does not necessarily refer to strong muscles or the ability to jog several miles. The fittest individuals are not necessarily the strongest, the smartest, or the healthiest. For example, it could be said that white four-o'clock flowers are less fit, not because they are sickly or smaller or have fewer flowers, but because they are not chosen by insect pollinators that prefer red flowers. In such a case, if insect pollinators prefer red flowers, they will not pollinate white or pink flowers, with the result that the white version of the gene will be underrepresented in subsequent generations. Therefore, the genes from the fittest individuals are those that are selected for in such a way that their proportion will increase in successive generations. The genes from less fit individuals are selected against and their proportion will decrease in successive generations.

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