The Structure of Evolutionary Theory

CHAPTER 11

The Integration of Constraint and

Adaptation (Structure and Function)

in Ontogeny and Phylogeny:

Structural Constraints, Spandrels,

and the Centrality of Exaptation in

Macroevolution

The Timeless Physics of Evolved Function

STRUCTURALISM'S ODD MAN OUTSIDE

In a famous passage from the Introduction to the Origin of Species, Darwin identified
the intricately adaptive character of most anatomical features as the primary
phenomenon that any theory of evolutionary mechanisms must explain. Many other
sources of information, he states, can easily prove evolution's factuality, but we will
not understand the causes of change until we can explain "how the innumerable
species inhabiting this world have been modified so as to acquire that perfection of
structure and coadaptation which most justly excites our admiration" (1859, p. 3).
Darwin felt that this striking and pervasive functionality of organic design
required an explicit functional theory of evolutionary causes rooted in the proposition
that adaptive structures originate "for" their utility. As functionalist theories, both
Lamarckian soft inheritance and Darwinian natural selection share a defining premise
that environmental information about adaptive design somehow passes to organisms,
and that organisms then respond by fashioning traits to enhance their competitive
ability within these environments. (Above all, functionalist theories require explicit
interaction of organism and environment in the service of improving local adaptation.
The pure imposition of one side upon the yielding properties of the other side does
not qualify.)
The strikingly different mechanisms of the two major functionalist theories—
organic response to felt needs for Lamarck, natural selection upon isotropic variation
for Darwin—should not obscure their agreement on the key functional principle that
adaptation drives evolution as organisms change to

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