Book excerpt: Among the offspring of humans and other animals are occasional individuals that are malformed in whole or in part. The most grossly abnormal of these have been referred to from ancient times as monsters, because their birth was thought to foretell doom; the less severely affected are usually known as anomalies. This volume digs deeply into the cellular and molecular processes of embryonic development that go awry in such exceptional situations. It focuses on the physical mechanisms of how genes instruct cells to build anatomy, as well as the underlying forces of evolution that shaped these mechanisms over eons of geologic time. The narrative is framed in a historical perspective that should help students trying to make sense of these complex subjects. Each chapter is written in the style of a Sherlock Holmes story, starting with the clues and ending with a solution to the mystery.