Evolution and Development II: DST & Reductionism

Evolution has resulted in organisms that develop. For a long time the processes of evolution and development have been theoretically and empirically largely independent. This was epitomized by the gene selectionist view of evolution, which rendered the process of development largely epiphenominal to the evolutionary business of evolving the genome. However, there is now a growing awareness that an understanding of development is essential to a complete understanding of evolution and vice versa. This session addresses what this 'developmental synthesis' may contribute and some difficulties that must be overcome for its success.

Organized by: Kelly Smith & Roger Sansom

Lee Zwanziger, National Academy of Science
"Reductionist Models in Developmental Biology"

Developmental biology, particularly morphogenesis such as theories of pattern formation, is a very useful conceptual laboratory in which to work on a sensible approach to reduction. Reduction, after all these years, is still important to conceiving of the how-questions that drive (at least a good deal of) biological understanding, but since biology is just as essentially historical (the objects of biological theory are essentially products of historical development), then any useable reductionism must accommodate time asymmetry and the balance of particular environmental contingencies plus vast ceteris paribus assumptions in order to come up with understanding. When we apply a set of reductionistic heuristics to questions of mechanism in a biological system under the overarching auspices of a not very reductionist model, such as an information-theoretic model, we get a complex picture, but one that is honestly and justifiably complex, not an example of mere theoretical eclecticism. The investigation of the Particular Model (say, the developing chick limb) via reductionistic heuristics under a Conceptual Model (information exchange) is more likely to result in the reification of the C-model and reductionistic use of it to work out an account of how a structure, e.g. the particular model comes about, than it is to push understanding of development in a non-reductionistic direction. [ Full Paper ]

Questions:

1. This paper depends on my conviction that accumulated historical contingency is a critical feature of biological systems and thus must be captured in biological explanation. How can that idea, if sensible, be clarified and refined?
2. This paper reflects my conclusions that theorizing in biology necessarily depends on invoking, and abstracting from, an overlapping series of models, ranging from the absolutely particular to the widest generality. If models are not necessary in this way, why and how else should we account for theory creation?
3. Finally, this paper reflects my observation that reductionistic research is critical to biology and properly so, but that it must be redescribed so as to escape the well developed reduction/antireduction debate cycle. If so, is there a more accurate way to do so than reductionistic research heuristics?

Jason Scott Robert, Brian K. Hall, and Wendy M. Olson, Dalhousie University
"DST Proposes, EDB Disposes? Integrating Approaches to Development and Evolution"

Many scientists, and very many commentators, are troubled by the relative isolation of developmental biology from evolutionary biology. Reconciling the science of development with the science of heredity preoccupied a minority of biologists for much of the twentieth century, but these efforts were not corporately successful. Mainly in the past fifteen years, however, these once dispersed integrating programs have been themselves synthesized and so reinvigorated. Two of these more recent synthesizing endeavors are evolutionary developmental biology (EDB) and developmental systems theory (DST). While the former is a bourgeoning and scientifically well-respected biological discipline, the same cannot (yet) be said of developmental systems theory. In this review, we provide overviews of DST and EDB, summarize their key tenets, and examine various ways in which DST relates to EDB. Three areas of special concern to us are: how DST and EDB bear on the study of epigenetics, which we define as causal mechanisms of development rather than a mechanism of inheritance; whether 'environment' should be understood (EDB-style) as a transgenerational constant or rather as inherited (DST); and the possibility that EDB already contains all the biologically worthwhile elements of DST. We conclude with some predictions about likely fruitful avenues for future inquiry where evolution meets development. [ Full Paper ]

Discussion Questions:

• Does a two-generational account of genetic transmission (including both zygotic and maternal genomes) suffice as an account of 'all that is inherited'?Ý
• Can processes be inherited?Ý
• How are mainstream evolutionary theory and Neo-Darwinian evolutionary theory challenged by DST's account of development?Ý
• If DST offers nothing practical to wet-bench scientists, should it receive less attention from philosophers of biology?ÝÝ More basically, does DST in fact offer nothing practical?

Julio Tuma, (University of Chicago
"The Biological Individual In-Formation"

Claims about information flow in ontogeny form a central part of the debate between researchers from the Developmental Systems perspective (DSTists) and those researchers who privilege the gene/genome (GPers) as playing a more programmatic or organizing role in development. DSTists point out that since mathematical information theory gives us no way of evaluating claims of source relevance, the choice of any given bit of information as signal (rather than noise) is somewhat relative. Relative, that is, to what one wants to count as holding content in the selection process. DSTists conclude that the only adequate (impartial) description of information flow need involve all regularly recurring developmental resources. This developmental egalitarianism is not shared by GPers who think that there is much to gain from a model that maintains the interactor/replicator distinction. Recent efforts (e.g. Maclaurin, 1998; Maynard Smith, 2000) to mediate between causal oversimplification and an abundance of explanatory developmental resources offer to extend information theory by stipulating what should count as informationally relevant or similarly put forward an account of what is intentional in selection. While these efforts and others to "clear up" what is meant by information in biology are laudable, they dispense with the problem of content or intentional relativity by replacing it with one of relativity in terms of trait assignment. More seriously, these accounts tend to miss (or at least, severely discount) what are potentially very important interactions in the developmental process. I offer an account that hopes to avoid these difficulties by focusing on the integration of functional roles within a developmental cycle rather than on the structural integrity so important to those who maintain the replicator/interactor distinction.