Causes of the Cambrian Explosion

The rapid diversification of animal species in the early Cambrian was the result of a range of interacting biotic and abiotic processes. Many hypotheses have been invoked to explain the rapid diversification of animal species in the early Cambrian (541 million to 515 million years ago), ranging from starbursts in the Milky Way to intrinsic genomic reorganization and developmental patterning. Recent hypotheses for the Cambrian explosion fall into three main categories: developmental/genetic, ecologic, and abiotic/environmental, with geochemical hypotheses forming an abundant and distinctive subset of the last ( 1 ). Most of these hypotheses have been posited as stand-alone processes that were the main cause of the explosion, yet many of them are tightly interlinked and codependent. The rapid diversification of animals in the early Cambrian is likely to have been the result of a complex interplay of biotic and abiotic processes (see the first figure).