Causes of the Cambrian Explosion.

Abstract

In the last decade, at least thirty individual hypotheses have been invoked to explain the Cambrian Explosion, ranging from starbursts in the Milky Way to intrinsic genomic reorganization and developmental patterning. It has been noted (1) that recent hypotheses fall into three categories: a) developmental/genetic, b) ecologic and c) abiotic environmental, with geochemical hypotheses forming an abundant and distinctive subset of the last. With a few notable exceptions, a significant majority of these hypotheses have been posited as stand-alone processes that constituted the principal causal modes of the Explosion. An additional challenge relates to the precise definition of the Explosion – is it the first appearance of animal groups, the diversification event, the emergence of marine ecosystems with ‘modern’ trophic structures, or all of these?