How to Explain Complexity (Adaptive, Non-Adaptive, and Irreducible)

Dan McShea
Biology Department, Duke University

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     Last modified: June 15, 2005
     Presentation date: 07/14/2005 2:00 PM in MACK 236
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Abstract
Evolutionists have never been able to offer an appealing explanation for adaptive complexity, meaning the extraordinary functional capabilities and structural intricacy of organisms. The consequences have been recurring overt challenges to evolution, and perhaps a broader skepticism as well, based on the supposed difficulty in explaining the vertebrate eye, the human brain, and other complex structures. The latest is a creationist challenge based on the “irreducible complexity” of the elaborate internal machinery of cells, the so-called “intelligent design” argument. The heart of the problem, I argue, is a conflation in evolutionary thought of two notions, adaptation – for which we have a perfectly good explanation (natural selection) – and organismal complexity, for which we don’t. Here I offer an explanation for complexity, pure complexity, divorced from any notion of adaptation. I call it the “internal-variance principle,” and it is based on Herbert Spencer’s metaphysics. The idea is simply that the accumulation of variation in any set of parts within an organism tends to make the parts more different from each other, and that this differentiation is a type of complexity. (“Adaptive complexity,” then, is just the subset of these ever-more complex variants that is also functional.) The principle predicts the existence of a vector, or drive, toward greater complexity, one affecting all lineages in all times and all places over the history of life. Thus, in this view, the complexity of organisms emerges as an expected feature of the evolutionary process, not a difficulty to be explained. Interestingly, the vector not only does not require selection, but there is reason to think that selection opposes it (that is, opposes complexity), and strongly!