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What is Evolution?

Biological evolution is the theory that all living things are modified descendants of a common ancestor that lived in the distant past. It claims that you and I are descendants of ape-like ancestors, and that they in turn came from still more primitive animals. This is the primary meaning of “evolution” among biologists. “Biological evolution,” according to the National Academy’ booklet, “explains that living things share common ancestors. Over time, evolutionary change gives rise to new species. Darwin called this process ‘descent with modification,’ and it remains a good definition of biological evolution today.” For Charles Darwin, descent with modification was the origin of all living things after the first organisms. He wrote in The Origin of Species: “I view all beings not as special creations, but as the lineal descendants of some few beings” that lived in the distant past. The reason living things are now so different from each other, Darwin believed, is that they have been modified by natural selection, or survival of the fittest: “I am convinced that Natural Selection has been the most important, but not the exclusive, means of modification.”

When proponents of Darwin’s theory are responding to critics, they sometimes claim that “evolution” means simply change over time. But this is clearly an evasion.No rational person denies the reality of change, and we did not need Charles Darwin to convince us of it. If "evolution" meant only this, it would be utterly uncontroversial. Nobody believes that biological evolution is simply change over time. Only slightly less evasive is the statement that descent with modification occurs. Of course it does, because all organisms within a single species are related through descent with modification. We see this in our own families, and plant and animal breeders see it in their work. But this still misses the point. No one doubts that descent with modification occurs in the course of ordinary biological reproduction. The question is whether descent with modification accounts for the origin of new species in fact, of every species. Like change over time, descent with modification within a species is utterly uncontroversial. But Darwinian evolution claims much more. In particular, it claims that descent with modification explains the origin and diversification of all living things. The only way anyone can determine whether this claim is true is by comparing it with observations or experiments. Like all other scientific theories, Darwinian evolution must be continually compared with the evidence. If it does not fit the evidence, it must be reevaluated or abandoned otherwise it is not science, but myth.