Inherency and homomorphy in the evolution of development

Organismal development occurs when expression of certain genes leads to the mobilization of physical forces and effects that shape and pattern multicellular clusters. All materials exhibit preferred forms, but the inherent morphological motifs of some, such as liquids and crystalline solids are well-characterized. Recent work has shown that the origin of the animals (Metazoa) was accompanied by the acquisition by their developing tissues of liquid-like and liquid-crystalline properties. This and the novel capacity to produce stiff internal substrata (basal laminae) set these organisms apart from their closest relatives by the propensity (predictable from their material nature) to form complex bodies and organs. Once functional forms became established, however, they were susceptible to further genetic change as well as partial or full supplanting of original physical determinants by different ones. This results in the increasingly recognized phenomenon of homomorphy, the presence of the same structure in descendent organisms, brought about by transformed developmental mechanisms.