The Structure of Evolutionary Theory

The Essence of Darwinism and the Basis of Modern Orthodoxy 125

Smith's laissez-faire economics, I believe that we achieve our best insight into the
essential claims of Darwinism and natural selection. First, and foremost, we grasp
the theoretical centrality of Darwin's conclusion that natural selection works
through a struggle among individual organisms for reproductive success. Darwin's
choice of levels, and his attempted restriction of causality to one level alone, then
becomes neither capricious nor idiosyncratic, but, rather, central to the logic of an
argument that renders the former "proof" of God's direct benevolence as an
epiphenomenon of causal processes acting for apparently contrary reasons at a
lower level. Second, we recognize the focal role of adaptation as the chief
phenomenon requiring causal explanation— for good design had also set the
central problem for English traditions in natural theology, the worldview that
Darwin overturned by deriving the same result with an opposite mechanism.
These two principles—the operation of selection on struggling organisms as
active agents, and the creativity of selection in constructing adaptive change—
suffice to validate the theory in observational and microevolutionary expression.
But Darwin nurtured far more ambitious goals (as the foregoing discussion of his
methodology illustrates, see pages 97-116): he wished to promote natural selection,
by extrapolation, as the preeminent source of evolutionary change at all scales and
levels, from the origin of phyla to the ebb and flow of diversity through geological
time. Thus, the third focal claim in the Darwinian tripod of essential postulates—
the extrapolationist premise— holds that natural selection, working step by step at
the organismal level, can construct the entire panoply of vast evolutionary change
by cumulating its small increments through the fullness of geological time. With
this third premise of extrapolation, Darwin transfers to biology the uniformitarian
commitments that set the worldview of his guru, the geologist Charles Lyell.

THE FIRST THEME: THE ORGANISM AS THE AGENT

OF SELECTION

Once the syllogistic core, * the "bare bones" mechanism of natural selection, has
been elucidated, two major questions—the foci of the next two sections

*By the "syllogistic core" of natural selection ("the bare-bones argument"), I

refer to the standard pedagogical presentation of the abstract mechanism of the

theory as a set of three undeniable factual statements followed by the inference of

natural selection (the fourth statement) as a logical entailment of the three facts, viz:

1. Superfecundity: all organisms produce more offspring than can possibly
   survive.


2. Variation: all organisms vary from other conspecifics, so that each
   individual bears distinguishing features.


3. Heredity: at least some of this variation will be inherited by offspring
   (whatever the mechanism of hereditary transition—a mystery to Darwin, but the
   argument only requires that heredity exist, not that its mode of action be known).


4. Natural selection: if we accept these foregoing three statements as factual (2
   and 3 ranked as "folk wisdom" in Darwin's time and could scarcely be doubted;
   while Darwin took great pains to validate 1 in early chapters of the Origin, showing,
   for example, that even the most slowly reproducing of all animals, the African
   elephant, would soon fill the