It is one of the best-known defenses of the theory of evolution, written by one of the best known evolutionists. It is a scientific theory only, and it has in recent years been challenged in the world of science-that is, not believed in the scientific community to be as infallible as it once was. Well, evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty.
Facts are the world's data.
Theories are structures of ideas that explain and interpret facts. Facts do not go away while scientists debate rival theories for explaining them. Einstein's theory of gravity replaced Newton's, but apples did not suspend themselves in mid-air pending the outcome. And human beings evolved from apelike ancestors whether they did so by Darwin's proposed mechanism or by some other, yet to be discovered. You might have been surprised by this opening.