Misconception: “Evolution is like a climb up a ladder of progress; organisms are always getting better.”

Response: It is true that natural selection weeds out individuals that are unfit in a particular situation, but for evolution, “good enough” is good enough. No organism has to be perfect. For example, many taxa (like some mosses, protists, fungi, sharks, opossums, and crayfish) have changed little over great expanses of time. They are not marching up a ladder of progress. Rather, they are fit enough to survive and reproduce, and that is all that is necessary to ensure their existence.

Other taxa may have changed and diversified a great deal—but that doesn’t mean they got “better.” After all, climates change, rivers shift course, new competitors invade—and what was “better” a million years ago, may not be “better” today. What works “better” in one location might not work so well in another. Fitness is linked to environment, not to progress.

Evolution is Random

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Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.