To Defend Evolution, One Must Understand It

In the Radiolab show just broadcast, I heard them make a rather common error in describing the idea of evolution. I wrote them this letter to point out the error, and why it matters:   Your program on laughter described chimps as "our ancestors." Similarly, it spoke of our having "inherited" something from them.   Chimps are not our ancestors; they're our cousins, with whom we share a common ancestor which was neither human nor chimp. This is more than a technical distinction, because this sort of confusion contributes significantly to scientific illiteracy. More than once someone has objected to the idea of evolution by asking me, "Why haven't other animals evolved?"   This question assumes the conception of evolution as a ladder with the different species as rungs -- rather than a tree the tips of whose branches are extant species, and whose lower levels are extinct ones. If one assumes this incorrect conception of evolution, there indeed is no good answer to the question. With the correct understanding, one can answer, "They have evolved. Their ancestors were different from them, and from anything existing today."