The near-simultaneous appearance of most modern animal body plans in the Cambrian explosion suggests a brief interval of rapid phenotypic and genetic evolution, which Darwin believed were too fast to be explained by natural selection. Lee et al. have now inferred the rates of these innovations by applying phylogenetic clock methods to the arthropods during this period. The rates of genetic and phenotypic evolution were shown to be ~4 times and ~5.5 times faster, respectively, than all subsequent parts of the Phanerozoic era — consistent with natural selection during the Cambrian explosion.