1208 THE STRUCTURE OF EVOLUTIONARY THEORY
organic shapes with the optimal forms directly produced by physical forces. He
regarded the correlation as a map of the actual efficient cause. This aspect of good
organic design does express a final cause in adaptation, but any evolutionary changes
must still must be crafted by an efficient cause—and Darwinian natural selection
generally acts as the efficient cause we seek for our explanations.
But before we dismiss Growth and Form as a brilliant and wonderfully written
disquisition rooted in a central error, we should pause to reflect upon the partial
validity of D'Arcy Thompson's theory of direct impress, or "order for free" in current
parlance (Kauffman, 1993). D'Arcy Thompson admitted that he could not apply his
theory to explain the groundforms of complex creatures, which he then accepted as
"givens" in his analysis of transformed coordinates. This admission scuttled more of
his hopes for generality than he was ever willing to acknowledge. But D'Arcy
Thompson's theory cannot be rejected as entirely, or even generally, wrong. Surely
his arguments for the hexagonal forms of crowded corallites, and the conformity of
the ends of hive cells to the Maraldi angle, are correct: organisms don't have genes
"for" hexagonality per se. Developmental genetics may regulate the types of
materials, and their rates and places of production. But hexagonal shapes probably
arise, just as for inorganic materials in similar conditions, by direct shaping under
laws of closest packing.
I am confident that biologists can trace the lineage of hippos deep into an
artiodactyl past in the early Cenozoic—as a genuine historical particular of unique
form, requiring a phylogenetic explanation. But when someone tells me that a
particular form of bacterium has not changed for 3.5 billion years because the oldest
of all fossils displays the same shape as some modern species, then I doubt that this
correct observation teaches me anything about filiation in a particular and continuous
lineage; whereas I may learn something about basic forms, homoplastically attained
again and again during the history of life, and therefore bearing no particular phyletic
message. And I may use D'Arcy Thompson's procedures to establish the probable
reasons behind these shapes, whether or not my explanations lie in direct shaping by
these physical forces (a strong possibility for the bacteria, but not for the hippos), or
in the adaptive values of designs actually built by the efficient cause of natural
selection.
ORDER FOR FREE AND REALMS OF RELEVANCE FOR
THOMPSONIAN STRUCTURALISMIn the most important modern work in the D'Arcy Thompsonian tradition, Kauffman
(1993, p. 443) "invites our attention to the central theme of this [that is, his] book:
Order in organisms may largely reflect spontaneous order in complex systems."
Kauffman retains strong feality to D'Arcy Thompson's central principle that the
adaptive order of biological systems arises by direct imposition of physical forces—
thus advocating an "externalist" form of structuralist thought that has not played a
large role in the history of evolutionary biology.