, Volume 21, Issue 5, pp 667-702
Date: 09 Feb 2007

Aggregate, composed, and evolved systems: Reductionistic heuristics as means to more holistic theories

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Richard Levins’ distinction between aggregate, composed and evolved systems acquires new significance as we recognize the importance of mechanistic explanation. Criteria for aggregativity provide limiting cases for absence of organization, so through their failure, can provide rich detectors for organizational properties. I explore the use of failures of aggregativity for the analysis of mechanistic systems in diverse contexts. Aggregativity appears theoretically desireable, but we are easily fooled. It may be exaggerated through approximation, conditions of derivation, and extrapolating from some conditions of decomposition illegtimately to others. Evolved systems particularly may require analyses under alternative complementary decompositions. Exploring these conditions helps us to better understand the strengths and limits of reductionistic methods.

The immediate stimulus for this analysis was Levins’ germinal essay “Complexity” (1973, from 1971 draft) and his distinction (1970) between aggregate, engineering, and evolved systems, which also influenced my 1974. The analysis of aggregativity began as class handouts in the Philosophy of Social Science and Philosophy of Biology courses that Levins and I co-taught at Chicago in the Winter and Fall quarters of 1971, later written up in my 1986b. I pointed Bechtel and Richardson to Levins’ work in the early 1970’s. They discuss this particular distinction on pages 25–26 of their superb and insufficiently appreciated (1992). Some properties of aggregativity are also noted by Nagel in his (1961) and classic, “Wholes, Sums and Organic Unities”—though we diverged in what we made of them. Stuart Glennan, Peter Taylor and Bill Bechtel gave especially useful comments on prior versions.