The Origins and Evolution of Animal Identity

The Darwinian synthesis focuses on speciation as the leading edge of evolution. But species are poor candidates for natural kinds because they are always susceptible to giving rise to something new. Physicalist evolutionary developmental biology presents an alternative scenario in which broad differences between organismal types were ontologically and temporally prior to subtypes and species-level variants. The cell masses that first developed into the metazoans, or animals, for example, arose from unicellular antecedents by a set of molecular innovations that constituted the embryos of these organisms as an unprecedented form of matter – liquid and liquid crystalline tissues – and thus a natural kind. This novel material embodied a set of morphogenetic processes and motifs that laid the basis for subsequent animal evolution. With the addition of other molecular functionalities simple “basal” metazoan body plans (sponges, placozoans) engendered more complex diploblasts (cnidarians, ctenophores) and bilaterian triploblasts (arthropods, chordates, mollusks, and so forth). Self-organizing patterning processes arising within these integrated communities of cells produced segments, appendages, patterned skeletons and organs. Bioelectrical scaffolding effects and the standardizing effects of development from an egg transformed phylotypic forms into canalized, integrated individuals that exist in the biosphere as “natural purposes,” causes and effects of themselves

The Origins and Evolution of Animal Identity

The Darwinian synthesis focuses on speciation as the leading edge of evolution. But species are poor candidates for bearers of well-defined biological identity because they are always susceptible to giving rise to something new. Physicalist evolutionary developmental biology presents an alternative scenario in which broad differences between organismal types were ontologically and temporally prior to subtypes and species-level variants. The cell masses that first developed into the metazoans, or animals, for example, arose from unicellular antecedents by a set of molecular innovations that constituted the embryos of these organisms as an unprecedented form of matter – liquid and liquid crystalline tissues – and thus a natural kind. This novel material embodied a set of morphogenetic processes and motifs that laid the basis for subsequent animal evolution. With the addition of other molecular functionalities simple “basal” metazoan body plans (sponges, placozoans) engendered more complex diploblasts (cnidarians, ctenophores) and bilaterian triploblasts (arthropods, chordates, mollusks, and so forth). Self-organizing patterning processes arising within these integrated communities of cells produced segments, appendages, patterned skeletons and organs. Bioelectrical scaffolding effects and the standardizing effects of development from an egg transformed phylotypic forms into canalized, integrated individuals that exist in the biosphere as “natural purposes,” causes and effects of themselves

The Origins and Evolution of Animal Identity

The Darwinian synthesis focuses on speciation as the leading edge of evolution. But species are poor candidates for bearers of well-defined biological identity because they are always susceptible to giving rise to something new. Physicalist evolutionary developmental biology presents an alternative scenario in which broad differences between organismal types were ontologically and temporally prior to subtypes and species-level variants. The cell masses that first developed into the metazoans, or animals, for example, arose from unicellular antecedents by a set of molecular innovations that constituted the embryos of these organisms as an unprecedented form of matter – liquid and liquid crystalline tissues – and thus a natural kind. This novel material embodied a set of morphogenetic processes and motifs that laid the basis for subsequent animal evolution. With the addition of other molecular functionalities simple “basal” metazoan body plans (sponges, placozoans) engendered more complex diploblasts (cnidarians, ctenophores) and bilaterian triploblasts (arthropods, chordates, mollusks, and so forth). Self-organizing patterning processes arising within these integrated communities of cells produced segments, appendages, patterned skeletons and organs. Bioelectrical scaffolding effects and the standardizing effects of development from an egg transformed phylotypic forms into canalized, integrated individuals that exist in the biosphere as “natural purposes,” causes and effects of themselves

Cell differentiation: what have we learned in 50 years?

I revisit two theories of cell differentiation in multicellular organisms published a half-century ago, Stuart Kauffman's global gene regulatory dynamics (GGRD) model and Roy Britten's and Eric Davidson's modular gene regulatory network (MGRN) model, in light of newer knowledge of mechanisms of gene regulation in the metazoans (animals). The two models continue to inform hypotheses and computational studies of differentiation of lineage-adjacent cell types. However, their shared notion (based on bacterial regulatory systems) of gene switches and networks built from them, have constrained progress in understanding the dynamics and evolution of differentiation. Recent work has described unique write-read-rewrite chromatin-based expression encoding in eukaryotes, as well metazoan-specific processes of gene activation and silencing in condensed-phase, enhancer-recruiting regulatory hubs, employing disordered proteins, including transcription factors, with context-dependent identities. These findings suggest an evolutionary scenario in which the origination of differentiation in animals, rather than depending exclusively on adaptive natural selection, emerged as a consequence of a type of multicellularity in which the novel metazoan gene regulatory apparatus was readily mobilized to amplify and exaggerate inherent cell functions of unicellular ancestors. The plausibility of this hypothesis is illustrated by the evolution of the developmental role of Grainyhead-like in the formation of epithelium

Form, function, mind: what doesn't compute (and what might)

The applicability of computational and dynamical systems models to organisms is scrutinized, using examples from developmental biology and cognition. Developmental morphogenesis is dependent on the inherent material properties of developing tissues, a non-computational modality, but cell differentiation, which utilizes chromatin-based revisable memory banks and program-like function-calling, via the developmental gene co-expression system unique to metazoans, has a quasi-computational basis. Multi-attractor dynamical models are argued to be misapplied to global properties of development, and it is suggested that along with computationalism, dynamicism is similarly unsuitable to accounting for cognitive phenomena. Proposals are made for treating brains and other nervous tissues as novel forms of excitable matter with inherent properties which enable the intensification of cell-based basal cognition capabilities present throughout the tree of life

The Origins and Evolution of Animal Identity

The Darwinian synthesis focuses on speciation as the leading edge of evolution. But species are poor candidates for natural kinds because they are always susceptible to giving rise to something new. Physicalist evolutionary developmental biology presents an alternative scenario in which broad differences between organismal types were ontologically and temporally prior to subtypes and species-level variants. The cell masses that first developed into the metazoans, or animals, for example, arose from unicellular antecedents by a set of molecular innovations that constituted the embryos of these organisms as an unprecedented form of matter – liquid and liquid crystalline tissues – and thus a natural kind. This novel material embodied a set of morphogenetic processes and motifs that laid the basis for subsequent animal evolution. With the addition of other molecular functionalities simple “basal” metazoan body plans (sponges, placozoans) engendered more complex diploblasts (cnidarians, ctenophores) and bilaterian triploblasts (arthropods, chordates, mollusks, and so forth). Self-organizing patterning processes arising within these integrated communities of cells produced segments, appendages, patterned skeletons and organs. Bioelectrical scaffolding effects and the standardizing effects of development from an egg transformed phylotypic forms into canalized, integrated individuals that exist in the biosphere as “natural purposes,” causes and effects of themselves

The Excessive Use of Presumptions and the Role of Subjective Employee Intent in Effectuating the Purposes of the National Labor Relations Act

This article will first examine the origin and development of significant presumptions and second, suggest a method by which the Board could better protect the Section 7 rights of employees without risking destabilization of the collective-bargaining process

The Evolutionary Origin of Digit Patterning

The evolution of tetrapod limbs from paired fins has long been of interest to both evolutionary and developmental biologists. Several recent investigative tracks have converged to restructure hypotheses in this area. First, there is now general agreement that the limb skeleton is patterned by one or more Turing-type reaction-diffusion, or reaction-diffusion-adhesion, mechanism that involves the dynamical breaking of spatial symmetry. Second, experimental studies in finned vertebrates, such as catshark and zebrafish, have disclosed unexpected correspondence between the development of digits and the development of both the endoskeleton and the dermal skeleton of fins. Finally, detailed mathematical models in conjunction with analyses of the evolution of putative Turing system components have permitted formulation of scenarios for the stepwise evolutionary origin of patterning networks in the tetrapod limb. The confluence of experimental and biological physics approaches in conjunction with deepening understanding of the developmental genetics of paired fins and limbs has moved the field closer to understanding the fin-to-limb transition. We indicate challenges posed by still unresolved issues of novelty, homology, and the relation between cell differentiation and pattern formation

Diphenylphosphinoyl chloride as a chlorinating agent - The selective double activation of 1,2-diols

© The Royal Society of Chemistry 2006Treatment of 1,2-diols with diphenylphosphinoyl chloride in pyridine produces beta-chloroethyl phosphinates which react with complete control of stereochemistry to give epoxides and azido-alcohols, useful intermediates in cyclopropane synthesis.David J. Fox, Daniel Sejer Pedersen, Asger B. Petersen and Stuart Warre