this particular specimen just happen to occupy the exact places that I needed a
priori to make my central point about lower choppings that destroy theories,
middle choppings that change theories in a Falconerian way (major alterations in
structure upon a preserved foundation), and upper choppings that change theories
in the lesser manner of Darwin's Milanese metaphor (smaller excisions that leave
the framework intact as well).
The central trunk (the theory of natural selection) cannot be severed, or the
creature (the theory) dies. (The roots, if you will, represent sources of evidence;
any one may be excised, if recognized as incorrect by later study, so long as
enough remain to anchor the structure). This central trunk then divides into a
limited number of major branches. These basic struts—the three
1 - 4. Agostino Scilla was also a celebrated painter as well as a scientist. The plates of his
1670 treatise are therefore particularly well done. This figure, representing a fossil coral
that Scilla found near Messina, fortuitously (and without any alteration whatsoever), pre-
sents a detailed picture of the basic logic of Darwinian theory as recognized in this book.
See text for details.Defining and Revising the Structure of Evolutionary Theory 19