1054 THE STRUCTURE OF EVOLUTIONARY THEORY
becomes something of a miscellaneous repository, as Seilacher (1970) recognized for
the same end member (that he called bautechnischer, or architectural). In particular,
the structural vertex includes two strikingly different subcategories, united in their
common appeal to physical consequences rather than functional crafting, but
otherwise strikingly disparate, even diametrically opposite, in their implications for a
key question, admittedly subsidiary to our present inquiry about structural vs.
functional origin, but of central importance to evolutionary study in general: namely,
the role of history and contingency in the interpretation of evolutionary lineages.
I shall consider these two structural categories seriatim, and in depth, in Chapter
11, and will therefore only present the basic conceptual framework here. In the first
category, some adaptive features of organisms may be directly molded by, or may
originate as immediate and deterministic consequences of, the physical properties of
matter and the dynamical nature of forces—in other words, not by an accumulative
process of functional honing through selection, and not (for that matter) by any
uniquely biological process at all. When Williams (1966) famously, if a bit
facetiously, remarked that we shouldn't consider a flying fish's capacity to fall back
into the water as an adaptation because their descent represents a necessary
consequence of physical mass—even though this capacity may be vital to the
continued life of the fish, and therefore strongly aptive—he invoked a direct physical
property of matter (not subject to alteration by selection at all in this case!).
D'Arcy Thompson's (1917, 1942) theory—that physical forces directly impose
an optimal biomechanical form upon plastic organic material—marks the admittedly
idiosyncratic locus classicus for this general attitude (see pp. 1179-1208). Stuart
Kauffman's (1993) interesting concept of "order for free" (good design automatically
generated by nature's laws, with no need for laborious construction by a particular
biological process like natural selection) provides the most fruitful current context for
this approach to aptive organic design.
In the second category that Darwin designated as "correlations of growth," and
Gould and Lewontin (1979) called spandrels, features arise nonadaptively as
physically necessary consequences of other changes that may (and, in all probability,
usually do) have an adaptive basis, or as inevitable and unselected sequelae of
general organic designs (that, again, generally arise for conventional functional
reasons).
Nonselected origin for structural reasons defines the common ground of the two
categories—directly generated by physical forces in the first, indirectly developed as
correlated consequences in the second. But the philosophical implications of these
two bases could not be more different in one crucial respect—hence the oppositional
stance often adopted between champions of the two modes, despite their
acknowledged common ground at the vertex of nonselected origin by physical
necessity.
Pure D'Arcy Thompsonians maintain little interest in history and phylogeny, and
may even become overtly hostile to the commanding influence of these concepts in
evolutionary biology. After all, if a trait arises by physical