This article summarizes a section from The World Book Encyclopedia that addresses the challenges facing the theory of evolution. Paleontologist Carroll Lane Fenton acknowledges that belief in evolution rests on certain evidence, but he also points out three key problems that remain unsolved: the cause of variations in nature, the mechanisms of natural selection, and the existence of missing evolutionary links in the fossil record. The article also highlights religious objections to evolution, based on interpretations of the Bible, the nature of God, and the Christian gospel.