Editing Cephalization (section)

=== Anterior Hox genes ===

Bilaterians have many more [[Hox gene]]s [[Evolutionary developmental biology|controlling the development]], including of the front of the body than do the less cephalized Cnidaria (two Hox clusters) and the Acoelomorpha (three Hox clusters). In the vertebrates, duplication resulted in the four Hox clusters (''HoxA'' to ''HoxD'') of mammals and birds, while another duplication gave [[teleost]] fishes eight Hox clusters. Some of these genes, those responsible for the front (anterior) of the body, helped to create the heads of both arthropods and vertebrates. However, the ''Hox1-5'' genes were already present in ancestral arthropods and vertebrates that did not have complex head structures. The Hox genes therefore most likely assisted in cephalization of these two bilaterian groups independently by [[convergent evolution]], resulting in similar [[gene network]]s.<ref name="Hombria 2021">{{cite journal |last=Hombría |first=James C.-G. |last2=García-Ferrés |first2=Mar |last3=Sánchez-Higueras |first3=Carlos |title=Anterior Hox Genes and the Process of Cephalization |journal=Frontiers in Cell and Developmental Biology |volume=9 |date=5 August 2021 |pmid=34422836 |pmc=8374599 |doi=10.3389/fcell.2021.718175 |doi-access=free}}<!--paper is CC-by-SA 4.0, could use image(s)--></ref>