The early evolution of Hox genes: a battle of belief?

Abstract

For more than a century the origin of metazoan animals and for less than three years the early evolution of Hox genes has been debated. Both discussions are intrinsically tied together. New data from whole genome sequencing and recent progress in phylogeny of basal metazoans allow to provide an answer. The evolution of diploblastic animals (Placozoa, Porifera, Ctenophora and Cnidaria) and Bilateria (all higher animals) went parallel. The early split of these two lineages led to the evolution of a Hox system in Bilateria and the presence of Hox-like genes in Cnidaria and Placozoa.