Inherency of form, mesoscopic materials and the physical origin of body plans

James (1890) described the soul as a simple substance in which psychic faculties and affections inhere.¹ Driesch (1908) wrote that the categories of substance and inherence apply most simply when things are regarded as bearers of properties.² Thompson (1992 edition of On Growth and Form) used the term in a physical sense. He wrote that a charge of either sign is inherent in the surface of a fluid drop. He added that such a charge tends to lower surface tension, because the surface molecules repel one another and so oppose their usual mutual attraction.⁵

Child (1924) reported a dispute over whether polarity and symmetry are inherent in protoplasm. Preformists, he wrote, assumed that they are inherent but can be altered by external factors.³ Child found no convincing evidence for this and much against it.³ He also argued that the constancy of axial pattern depends on the conditions of development, and that it disappears when those conditions are altered beyond a limit.³ In his account, physiological gradients are not inherent in protoplasm. They arise in a reaction to a local or differential external factor, and the relation is quantitative and dynamic, not specific or material.⁴

Newman (2019) placed inherency in the physical state of multicellular masses. The properties relevant to morphogenesis and pattern formation are those of mesoscopic materials, such as liquid and liquid-crystalline tissues, and of extended excitable media. These include diffusion, reaction and synchronization of oscillations.⁶ Mesenchymes and connective tissues are not liquid tissues by Newman's definition. They are still biogeneric materials, viscous, viscoelastic or solid depending on their extracellular matrix. Cell condensation is one inherent form of these tissues, and condensations are the primordia of hairs, teeth, feathers and the bones of vertebrate fins and limbs.⁷ Newman noted that inherency applied only once such materials existed as multicellular masses. Gene innovations confined to Metazoa were needed to constitute them.⁸

Fábregas-Tejeda and Sims (2025) described how evolutionary developmental biology moved on. The search for master control genes proved overly simplistic. It gave way to modelling gene regulatory networks and to wider causal-mechanistic accounts of development.⁹ In their list of phenotype-generating mechanisms, they included generic mesoscale physical forces and dynamical patterning modules, citing Newman and Bhat (2009).⁹ The physical account of form is thus treated as one line of work beside gene-network studies, not as a replacement for them.⁹