Major Movements in Psychology

Sociobiology and Evolutionary Psychology

What is natural selection?

Natural selection refers to the effect of the natural environment on the likelihood that genetically based traits will be passed on from one generation to the next. The process goes like this: First there must be variation in a particular trait within a population. Secondly, the trait must have some genetic basis. Thirdly, one version of the trait is better adapted to the environment than another version. Consequently, the animals with the more adaptive trait will bear more young, thus passing more of their genes onto the next generation.

Let’s consider the example of light and dark moths first recorded by Charles Darwin. There were two varieties of moths in England, light-colored moths and dark-colored moths. Originally, there were more light-colored moths than dark ones, as the dark ones stood out against the light-colored tree bark and were easy prey for the local birds. At this point, light color was more adaptive than dark color.

During the Industrial Revolution in England, however, the trees became covered with soot. This meant the dark-colored moths were better adapted to their environment than the light-colored moths, as they no longer stood out against the soot-covered tree bark. Now it was the light-colored moths that were easy prey for the birds. Hence, the population of dark-colored moths grew relative to the population of light-colored moths as more of the former survived to reproduce and pass their genes on to the next generation. Thus natural selection acted on the moth population as a result of their coloring. Of note, Darwin’s concept of natural selection does not explain how variation in the population comes to be, only how one trait comes to be more frequent in the population than another trait.


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