The Theory of Natural Selection

In the 1800s, Charles Darwin, a British naturalist, developed the theory of natural selection in his book “On the Origin of Species by Means of Natural Selection”. Darwin had the opportunity to travel around the world as the naturalist on a British survey ship. Wherever Dar­win visited, he saw a large number of different kinds of plants and animals and noted how well they were adapted to their particular situations.

He determined that there were several factors that could interact together to allow for natural selection:

1. Individuals within a species showed variation; some of the variations were very useful and others were not. For example, individual animals that are part of the same species show different colour variations. Some colours make the animal more conspicuous while others are less conspicuous.

2. Organisms within a species typically produce many more offspring than can survive. This means that here is not enough suitable habitat for all of the offspring to grow to maturity. A pair of rabbits may have three to four litters of offspring each sum­mer with several young in each litter.

3. Because of the excess number of individuals, there is a struggle for survival. Individuals within the population must compete with each other for food, space, mates, or other requirements that are in limited supply.

Great horned owls and other large owls typically produce two young at a time, but if food is in short supply, the larger of the two young will get the majority of the food.

4. Because of variation among individuals, some would have a greater chance of surviving and reproducing than others. The competition for resources often results in the less fit individuals dying; therefore, they do not get a chance to reproduce themselves. Even if they do not die, they may mature more slowly and not be able to repro­duce as many times as the more fit members of the species.

5. As time passes and each generation is subjected to the same kind of process, there will be an increase in the percentage of individuals showing the favorable variations and a decrease in those having unfavorable variations. The species will become better adapted to its environment.

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