1198 THE STRUCTURE OF EVOLUTIONARY THEORY
construction, of the underlying Bauplan—cannot be gainsaid at this level of
complexity. (With refreshing candor, D'Arcy Thompson admits that he had tried his
best "to circumscribe the employment of the latter [that is, of heredity] as a working
hypothesis in morphology.") D'Arcy Thompson writes, in his key statement (p. 715):
It would, I dare say, be a gross exaggeration to see in every bone nothing
more than a resultant of immediate and direct physical or mechanical
conditions; for to do so would be to deny the existence, in this connection, of
a principle of heredity. And though I have tried throughout this book to lay
emphasis on the direct action of causes other than heredity, in short to
circumscribe the employment of the latter as a working hypothesis in
morphology, there can still be no question whatsoever but that heredity is a
vastly important as well as a mysterious thing; it is one of the great factors in
biology... But I maintain that it is no less an exaggeration if we tend to
neglect these direct physical and mechanical modes of causation altogether,
and to see in the characters of a bone merely the results of variation and of
heredity, and to trust, in consequence, to those characters as a sure and certain
and unquestioned guide to affinity and phylogeny.This admission then leads to a recovery of relevance via the second argument,
presented in his last and, in the judgment of most biologists, his most important
chapter "on the theory of transformations, or the comparison of related forms." All
professional evolutionists know D'Arcy Thompson's famous diagrams of related
organisms compared by imposing a Cartesian grid upon one form, treated as a
reference, and then rendering other forms as results of simple distortions and
transformations of the grid lines (see Figure 11-6 for an example). But I think that
most of us have not understood the logical and theoretical reasons behind D'Arcy
Thompson's invention, largely because (as for the chapter "on magnitude") we read
this section out of context, and do not grasp its intimate relation (as an apotheosis,
given the limitations he had to admit) to his general and idiosyncratic theory of form.
That is, we tend to interpret these Thompsonian transformed coordinates as a
crude, and ultimately failed, attempt to operationalize (by pictorialization) a good
intuition about the multivariate nature of evolutionary change before the development
of appropriate statistical techniques, and the invention of computers, permitted us to
apply genuine multivariate mathematics to problems of form. Most of us, I think,
envisage the deformed coordinate grid as a mere residuum of a qualitative analysis
focused on the transformed bodies themselves—just a set of guidelines needed to
make a crude map of the organisms under consideration.
In so doing, we misunderstand D'Arcy Thompson's intention in a precisely
backwards manner. His interest lay primarily in the lines of the stretched and
deformed grids, for he had remained true to his theory that physical forces shape
organisms directly. He had made a painful and necessary surrender of that theory—
by bowing to conventional evolutionary resolutions in terms of