We argue that the physics of complex materials and self-organizing processes should be made central to the biology of form. Rather than being encoded in genes, form emerges when cells and certain of their molecules mobilize physical forces, effects, and processes in a multicellular context. What is inherited from one generation to the next are not genetic programs for constructing organisms, but generative mechanisms of morphogenesis and pattern formation and the initial and boundary conditions for reproducing the specific traits of (...) a taxon. There is no inherent antagonism between this “physicalist” perspective and genetics, since physics acts on matter, and gene products are essential material components of living systems whose variability affects the systems’ parameters. We make this notion concrete by summarizing the concept of “dynamical patterning modules” (DPMs; Newman and Bhat, Phys Biol 5:1–14, 2008; Int J Dev Biol 53:693–705, 2009), an explicit physico-genetic framework for the origin and evolution of multicellular form in animals, as well as (when differences in interaction toolkit genes and applicable physical processes are taken into account) in multicellular plants (Hernández-Hernández et al., Int J Dev Biol 56:661–674, 2012). DPMs provide the missing link between development and evolution by revealing how genes acting in concert with physics can generate and transform morphology in a heritable fashion. (shrink)

Much of the philosophical attention directed to Kant’s intervention into biology has been directed toward Kant’s idea of a transcendental limit upon what can be understood constitutively. Kant’s own wider philosophical practice, however, was principally oriented toward solving problems and the scientific benefits of his methodology of teleology have been largely underappreciated, at least in the English language literature. This paper suggests that all basic biology has had, and continues to have, a need for some form of heuristic “bracketing” and (...) that a renewal of some form of, albeit flexible, teleological methodological bracketing can better complement the productive assimilation into developmental biology of continuing advances in our understanding of the mesoscale physics and chemistry of soft, excitable condensed matter, than what has been the prevailing and de facto use of a form of bracketing shaped by the neoDarwinian Modern Synthesis. Further we offer a concept of biogeneric processes and a framework of physico-genetic “dynamical patterning modules”, that can begin to account for the appearance of new Kantian “stocks of Keime und Anlagen”, capable of potentiating some range of possible organismal forms, and provide grounds for moving up the teleological “goalposts”, i.e., expanding the range of what can be accounted for on a constitutive basis. (shrink)

During vertebrate limb development, various genes of the Hox family, the products of which influence skeletal element identity, are expressed in specific spatiotemporal patterns in the limb bud mesenchyme. At the same time, the cells also exhibit ‘self‐organizing’ behavior – interacting with each other via extracellular matrix and cell‐cell adhesive molecules to form the arrays of mesenchymal condensations that lead to the cartilaginous skeletal primordia. A recent study by Yokouchi et al.(1) establishes a connection between these phenomena. They misexpressed the (...) product of the Hoxa‐13 gene in chick limb buds and demonstrated both skeletal pattern perturbations and changes in cell‐cell adhesivity in mesenchyme aberrantly expressing this protein. (shrink)

When two populations of cells within a tissue mass differ from one another in magnitude or type of intercellular adhesions, a boundary can form within the tissue, across which cells will fail to mix. This phenomenon may occur regardless of the identity of the molecules that mediate cell adhesion. If, in addition, a choice between the two adhesive states is regulated by a molecule the concentration of which is periodic in space, or in time, then alternating bands of non‐mixing tissue, (...) or segments, can form. But temporal or spatial periodicities in concentration will tend to arise for any molecule that is positively autoregu‐latory. It is therefore proposed that segmentation is a ‘generic’ property of metazoan organisms, and that metamerism would be expected to have emerged numerous times during evolution. A simple model of segmentation, based solely on differential adhesion and periodic regulation of adhesion, can account for segment properties as disparate as those seen in long and short germ band insects, and for diverse experimental results on boundary regeneration in the chick hind brain and the insect cuticle. It is suggested that the complex, multicom‐ponent segment‐forming systems found in contemporary organisms (e.g., Drosophila) are the products of evolutionary recruitment of molecular cues such as homeobox gene products, that increase the reliability and stability of metameric patterns originally templated by generic self‐organizing properties of tissues. (shrink)

This book is concerned with, and makes an important contribution to, answering the central question of evolutionary theory: By what mechanisms and processes do organisms undergo transformative change? Animals or plants may undergo alterations in morphology or activity during their lifetimes, but only if such alterations are conveyed to the next generation can they contribute to the establishment of new forms. Heritability by itself is not decisive: offspring can differ from their parents at a variety of genetic loci without this (...) constituting evolutionary change, notwithstanding the fact that on theoretical grounds the standard model, stemming from the Modern Synthesis, asserts that any such variation represents incipient evolution (i.e., evolution is change in allele frequency). Clearly, some gene changes make more of an evolutionary difference than others. By placing phenotype at center stage and treating genotypes not in terms of their selective advantage, but rather with respect to the changes they exert on the phenotype, the author subtly but significantly reorients the explanatory terrain of evolutionary theory. (shrink)