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CHAPTER 7 Integrated Mechanisms 1. INTRODUCTION: REPLACING A DIRECT LOCALIZATION Analysis into localized components and their interactions is a fruitful scientific strategy when the system under study is nearly decomposable; that is, when the organization is relatively simple. In defending near decomposability as a heuristic for human problem-solving, Simon offers two markedly different kinds of reasons in its favor. First, given the resource limitations of human beings, near decomposability is an assumption that enables us to deal efficiently with complex systems. This is a kind of naturalistic grounding for simplicity. Second, simply or nearly decomposable systems are more likely to evolve.1 We have already pointed out that Simon's second reason is less plausible than his first: Evolution works with functioning systems and modifies them to carry out new tasks and meet new demands; it is not creation de novo, but descent with modification. Modifying an existing system may entail altering some ofits parts, but this is accomplished by adjusting extant structures to fit new demands. This theory lies at the heart of appeals to evolutionary constraints. 2 As Darwin said, initially appealing to similarities in developmental stages, We can clearly understand, on the principle of variations supervening at a rather late embryonic period, and being inherited at a corresponding period, how it is that the embryos of wonderfully different forms should still retain, more or less perfectly, the structure oftheir common progenitor.... Thus we can understand how it has come to pass that man and all other vertebrate animals have been constructed on the same general model. (1871, p. 32) This development through descent neither depends upon nor creates decomposability . If anything, the mutual coevolution of parts will compromise what decomposability there is and make the system more integrated functionally. Problems ofthe sort we will discuss in this and the next chapter present especially difficult problems for localization and decomposition as research strategies because the systems involved exhibit a more complex form of organization. Within some systems, processes depend on the integration of lower-level components, rather than on just their weak interaction . These are functionally integrated systems. A research strategy that 150 . III. Elaborating Mechanisms decomposes a hierarchically integrated system into units exhibiting independence or quasi-independence will not identify the processes that result from the integration of the system. Simon characterizes the kinds of nearly decomposable systems with which he is concerned as hierarchical, but he explicitly notes that in so doing he is not requiring that hierarchies incorporate subordination of function. This is one important feature of integrated functions in complex systems: they provide a means by which one component can exercise control over other components. To capture the idea that, in some hierarchies, higher levels exercise control over lower levels, Pattee (1973) introduces a distinction between what he calls structural hierarchies and control hierarchies. Structural hierarchies are Simon's hierarchical systems. In control hierarchies, demands on systemic function affect constituent behavior , and the mode of organization has the consequence that the interactions between components at one level can alter the behavior of the constituents of these components; that is, processes explicable at a higher level alter processes at lower levels. 3 The result, Pattee claims, is that we can no longer identify a sharp cleavage between levels in nature and thereby develop dynamic theories at one level while ignoring or averaging over processes at others: In a control hierarchy the upper level exerts a specific, dynamic constraint on the details ofthe motion at the lower level, so that the fast dynamics ofthe lower level cannot simply be averaged out. The collection of subunits that forms the upper level in a structural hierarchy now also acts as a constraint on the motions of selected individual subunits. This amounts to a feedback path between levels . Therefore, the physical behavior of a control hierarchy must take into account at least two levels at a time. (Ibid., p. 77) Control hierarchies, as far as we understand them, result from the way a system is organized. In functionally integrated systems the behavior ofthe components is interdependent, so a change in the behavior of one part alters the behavior of others. Thus, the systems are self-organizing because of the integration and interdependence of component functions. As with the cases discussed in the previous chapter, the focal case we consider in this chapter-research on fermentation and muscle glycolysis -began with an assumption of simple decomposability that shifted to near decomposability. Fermentation was assumed to involve a series of...

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