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Developmental Systems Theory Chapter 5 Developmental Systems Theory and “Fuzzy” Organisms “It’s not human until we say it’s human” T he previous chapter highlighted the centrality of selfdirection in determining the status of a developing entity. It was the proximate and active potential to self-direct its own development that grounded the claim that the embryo is human. Collections of cells with only the proximate potential to become human could not be regarded as human since, in such a case, they would not be exhibiting what Whelton called an internal principle of motion and rest (soul). In dramatic contrast to this view, it is precisely the claim that there is anything self-directing in development that is called into question by some versions of developmental systems theory.1 1. The general school of thought known as systems theory goes by a variety of names, including “developmental systems theory” (or “DST”), “systems biology,” “systems approach” or “systems view.” 133 134 Developmental Systems Theory The Role of Non-genetic Factors in Development The primary focus of systems theory is not the ontological status of the embryo. Rather, the central concern is to show that the developmental activity observable in any organism, including embryos, cannot be reduced to the agency of a single part. Such activity is best explained as an effect of the whole complex of parts, which act upon and regulate one another. This claim obviously puts systems theorists at odds with Aquinas and Aristotle, as well as with Whelton, Ashley, and Moraczewski (discussed in the previous chapter), all of whom argue or imply that development is controlled by a central organ. In practice though, the systems view is typically contrasted against what Jason Scott Robert refers to as the “genes only” or “genes-plus” view of biology;2 namely, one in which the genome is seen as containing all or most of the “information” necessary for development, thereby singling out the genome as the primary or exclusive agent of development. Robert succinctly contrasts the systems view to the genes-only view as follows: A standard interpretation [i.e., the genes-only view] is that the inherited genome initiates and directs development, and that we can understand the development of organisms best by beginning with the genome and investigating the minutiae of gene activation. I contend that this interpretation is misguided, that there is much more to development than the activation of genes, and that the genome may be the wrong place to start in understanding development.... To take development seriously is ... to explore in detail the processes and mechanisms of differentiation, morphogenesis, and growth, and the actual (not ideologically or perhaps merely technologically inflated) roles of genes in these organismal activities.3 When taken in this general form, the point of systems theory is straightforward: developmental biology has uncovered many examples of non-genomic structures interacting and cross-regulating the developmental process. Recall the earlier discussion of the interaction of sperm and egg-derived molecular components prior to syngamy. There, for ex2 . Cf. Jason Scott Robert, Embryology, Epigenesis, and Evolution: Taking Development Seriously (Cambridge: Cambridge University Press, 2004). 3. Robert, Embryology, Epigenesis, and Evolution, xiii. Developmental Systems Theory 135 ample, we saw the sperm (not the DNA within the sperm) initiating a block to polyspermy simply by coming into contact with the membrane of the oocyte. Furthermore, once the membrane was penetrated, preexisting proteins within the sperm facilitated the second meiotic division of the oocyte nucleus—a clear step in the developmental process. Furthermore, as Robert notes, the actual expression of a gene depends on a variety of “environmental” factors acting both within and among the cells of a developing organism:4 gene “activation” is irreducibly spatiotemporal, depending on the developmental history of the particular cell in which it is located—particularly, the cell’s location in the developing embryo and the number of times the cell line that leads to it has divided. Thus, it is evident that genes are not passive providers of encoded instructions that retain their structure across generations .... In short, in the production of an organism, segments of DNA interact with proteins, metabolites, nutrients, and other segments of DNA according to a specifically structured (though flexible) schedule within a specifically structured (though not invariant) environment which enables such interactions and which is necessary for their occurrence.5 Even if one grants that the genome contains all or most of the “information ” required for successful development, the determination of where, when, and in what...


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