Natural Selection and Adaptations in Action

In This Chapter

^ Understanding the types of selection ^ Seeing selection in action ^ Knowing an adaptation from an exaptation ^ Examples of selection in action

£ volution is nothing more — or less — than changes in the relative frequencies of heritable traits in a group of organisms (whether particular populations or whole species) over time. Simple enough.

But what causes traits to change over time? Often, it's natural selection, the process whereby some individuals, as a result of possessing specific traits (keener eyes, bigger leaves, etc.) leave more descendants than other individuals that lack these traits. If these advantageous traits are heritable (and thus are passed on to offspring), then over time, as some traits are favored and others are selected against, populations change — they evolve. Eyesight gets keener because the individuals with weaker eyes are not passing the genes for weaker eyes to future generations. Changes that are the result of natural selection are adaptations. In this example, keener eyes is an adaptation, as are bigger leaves.

Natural selection is not a difficult concept, but many people get all confused about it — particularly when it comes to differentiating between the process of selection (how it works) and the results of selection (the adaptations). This chapter helps you sort everything out.

Natural selection is only one of the mechanisms that cause evolution. Another mechanism — genetic drift — is the topic of the next chapter.

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