Inherent forms and the evolution of evolution

Abstract

John Bonner presented a provocative conjecture that the means by which organisms evolve has itself evolved. The elements of his postulated nonuniformitarianism in the essay under discussion—the emergence of sex, the enhanced selection pressures on larger multicellular forms—center on a presumed close mapping of genotypic to phenotypic change. A different view emerges from delving into earlier work of Bonner's in which he proposed the concept of “neutral phenotypes” and “neutral morphologies” allied to D’Arcy Thompson's analysis of physical determinants of form and studied the conditional elicitation of intrinsic organizational properties of cell aggregates in social amoebae. By comparing the shared and disparate mechanistic bases of morphogenesis and developmental outcomes in the embryos of metazoans (animals), closely related nonmetazoan holozoans, more distantly related dictyostelids, and very distantly related volvocine algae, I conclude, in agreement with Bonner's earlier proposals, that understanding the evolution of multicellular evolution requires knowledge of the inherent forms of diversifying lineages, and that the relevant causative factors extend beyond genes and adaptation to the physics of materials.

The Lithbea Domain

“…Third: Evolution that evolves. S. Newman, [ 95 ] in an interesting reflection on the inherent forms and the evolution of evolution, argues that “Once a novel kind of biological matter has been constituted, evolution is channeled in new, preferred directions, ….”. In this direction, it is possible to speculate that new rules may appear in the evolution of some of the synthetic living beings because their creation is not the result of a natural process (it has not been tested by natural selection), but of direct changes in the genetic program or the development of new synthetic beings.…”

Interplay of mesoscale physics and agent-like behaviors in the parallel evolution of aggregative multicellularity

“…The physical framework addressed here provides a complement, or even an alternative, to the multilevel selection and scale-based accounts. As described above, despite the fact that animals, Dictyostelia and Myxobacteria can all be conceptualized as non-living liquids, the weaker associations between cells and surfaces in the social amoebae and bacteria lead to behaviors not observed in animals (e.g., streaming) and the stronger, cytoskeletally linked attachments in animals mediate behaviors (multilayering and lumen formation) not seen in the aggregative systems [15]. These differences are amplified by the fact that polarity (affecting, variously cell surface or shape in the different systems) is much more transient in Dictyostelia and Myxobacteria than in animals [65,179,180], undermining the persistence of complex organization in the former two groups.…”

“…There appear to be ecological determinants (e.g., resource availability, land vs. water environment) of whether organisms are clonal or aggregative [ 9 , 12 , 13 ]. Furthermore, clonal lineages do not always exhibit complex development with different cell types and arrangements, and aggregative ones often do [ 3 , 14 , 15 ].…”

Unmodern Synthesis: Developmental Hierarchies and the Origin of Phenotypes

“…Waddington introduced the concept of epigenetics to help elucidate the morphogenetic and historical factors that act in conjunction with genes to produce adult phenotypes (for a review of the concept see). Some extended synthesis proponents have used the term in a similar manner, suggesting that the dynamical patterning networks that emerge from the reciprocal interactions of cells, secreted morphogens, and genes are the true purveyors of phenotypes . For these individuals, “epigenetics” refers to a suite of morphogenetic mechanisms that are often neglected in traditional molecular studies, which almost always focus heavily, or exclusively on genetics.…”