Ten questions to ask your biology teacher about evolution. ORIGIN OF LIFE. Why do textbooks claim that the 1953 Miller-Urey experiment shows how life's building blocks may have formed on the early Earth -- when conditions on the early Earth were probably nothing like those used in the experiment, and the origin of life remains a mystery? DARWIN'S TREE OF LIFE. Why don't textbooks discuss the "Cambrian explosion," in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor -- thus contradicting the evolutionary tree of life? HOMOLOGY. Why do...