Pigliucci, Muller: Evolution, extended synthesis

For me this collection of 17 articles was thrilling insight into insider thinking about evolution today. Taken back to front, it moves from an overview of dialectic within science itself, even of science's place within culture, through dialectic within evolutionary biology, through recognition of the disunity that's always marked the Modern Synthesis, through considerations of modern trends in biology that further amplify that disunity, to detailed analyses of specific current controversies through which discourse for framing evolutionary theory is being extended.

Challenges to the Modern Synthesis appearing in the book Massimo marshals into clusters in his introduction: Gradualism--"various kinds of mechanisms for discontinuous change are now known from the domains of genome evolution, phenotypic plasticity, epigenetic development and nongenetic inheritance." Externalism--"organisms themselves represent determinants of selectable variation and innovation. At the theoretical level this shifts a significant portion of the explanatory weight from the external conditions of selection to the internal generative properties of evolving phenotypes." Gene centrism--"several contributions to this volume converge on the view of 'genes as followers' in the evolutionary process, ensuring... the progressive fixation of phenotypic traits that were initially mobilized through plastic responses of adaptative development systems to changing environmental conditions. In this way, evolution progresses through the capture of emergent interactions which are passed on and elaborated on in subsequent generations." I was left with an impression of the Modern Synthesis dissolving into incoherence, its original appearance of coherence having been much of a myth in the first place.

Teleology is taken into consideration briefly at the end of the book, only to be summarily rejected. Throughout, human conscious judgement and volition is assumed merely through each author's opinions being thought worth the attention of a reader, yet no one considered the implications of that talent being a creation of the process of evolution. That is, teleology appears to be involved by someone undertaking the conceiving and planning of the conference this book was based on, participation in the discussion of the issues raised, and the process of publishing the contributions, yet no one explores where such an appearance of teleology might originate in our evolutionary past. Generally the authors’ attitude to the Modern Synthesis is to note challenges to it but not to judge whether those challenges actually contradict it. In this sense the book perfectly fulfills its title. It extends the Modern Synthesis, but does not challenge it.

Here are quotes from the end of the book, in reverse order:

Werner Callebaut:

Let me conclude. Ever since its inception, the synthesis has been characterized by “lateral” and “vertical” extensions and by simultaneous disunifying tendencies, with no end in sight…

It remains to be seen if, in a broader social and cultural embedding, “evolution” (or at least a “gene’s eye” variety) will retain the aura of austerity that someone like George Williams (1966) cast on the theme almost half a century ago. Or will it, rather, function as ersatz religion, not unlike Huxley’s and E. O. Wilson’s secular humanism, but now for the masses (the “new atheism”)?...

[The Synthesis] is first and foremost a loosely and flexibly structured network of concepts and models rather than a “theory” according to old-style hypothetico-deductivism.

[Quote from Douglas Futuyama]: By and large, naturalists and systematists absorbed rather little of the population-genetic theory that is the core of neo-Dawinism: but it must be granted that, for decades after the Synthesis, few if any comprehensive treatments of population genetics explained the implications of the equations for evolutionary studies, especially in terms that a nonmathematical biologist could understand…

[Quote from E. O. Wilson]: some of the apparent new understanding of the Modern Synthesis was false illumination created by the too-facile use of a bastardized genetic lexicon: “fitness,” “genetic drift,” “gene migration,” “mutation pressures,” and the like. So many problems seemed to be solved by invoking these concepts, and so few really were. Stagnation inevitably followed…

Rather than revolutionary upheaval, the language of extension propounded in the present volume suggests to me “accommodation” in the Piagetian sense… of accommodating an old “schema,” the Synthesis, to new “objects,” namely, the areas of biology that it [the synthesis] left out or “blackboxed.”

Gerd B. Muller:
This shift from a predominantly statistical and correlational approach to a causal-mechanistic approach is one of the main characteristics of the Extended Synthesis.

The origin of novelty and its role in the evolution of phenotypic complexity represents an evolutionary problem that had been sidelined by the Modern synthesis, due to its focus on variation and population dynamics.

Evolutionary developmental biology reemphasizes the phenotype in addressing the mechanistic factors in organismal change…. The inclusion of EvoDevo concepts in general, and of epigenetic innovation theory in particular, entails not only a conceptual widening but also a shift of emphasis in some of the traditional elements of the Modern Synthesis. One is the reduction of the overreliance on facile genetic explanations of organismal form and diversity…. EvoDevo demonstrates that knowledge of the rules of the processes that intervene between genotype and phenotype is necessary for understanding the causalities of biological form.

In this interpretation, natural selection functions to release inherent developmental potential and to explore the residual plasticity of developmental systems, but the specificity of the phenotypic outcome is determined by the capacities of the developmental systems undergoing change.

Stuart A. Newman:
A striking aspect of the metazoan radiation is the fact that a common set of highly conserved gene products, the developmental-genetic tool kit…has been used to a nearly exclusive extent to generate animal body plans and organ forms for more than half a billion years… A surprising number of the tool kit genes, including some that have key roles in morphogenesis and pattern formation, are found in the genome of M. brevicollis, an exclusively unicellular choanoflagellate… a few additional genes appear in the tool kit concomitant with the emergence of the sponges, and a few more are found in the simplest eumetazoans, the cnidarians. The Cambrian explosion followed with no more significant additions to the tool kit.

Below, microdata: