The recent surge in interest in the origins of multicellular animals (metazoans) is fueled by new evidence from three major sources: molecular sequencing, the study of evolutionary development and the discovery of exceptionally preserved fossils of Precambrian and Cambrian age, particularly from China. Genetic sequences provide a means of analyzing how the major animal groups are related and of estimating their time of origin (using the molecular clock) — a means that is independent of morphological data and the record of evolutionary events the fossils reveal. The study of developmental processes in an evolutionary framework ("evo-devo") provides the link between...