sence both because the logical structure of the theory so dictates, and because the
history and current utility of the theory so document.
To complement this most general statement with just one example of the
utility of historical analysis at the smaller scale of details, I offer the following case
as the strongest argument for my central claim that Darwin's brave attempt to
construct a single-level, exclusively organismic theory of natural selection must
fail in principle, and that all selectionists must eventually own a hierarchical
model. What better evidence can we cite than the historical demonstration (see
Chapters 3 and 5 for details) that each of the only three foundational thinkers who
truly understood the logic of selectionism—August Weismann, Hugo de Vries, and
Charles Darwin himself—tried mightily to make the single-level version work as a
fully sufficient explanation for evolution. And each failed, after intense intellectual
struggle, and for fascinatingly different reasons documented later in the book—
Darwin for explaining diversity by reluctant resort to species selection; Weismann
for a strongest initial commitment to a single level, and an eventual recognition of
full hierarchy as the most important and distinctive conclusion of his later career
(by his own judgment); and de Vries for reconciling his largely psychological
fealty to Darwin as his intellectual hero, with his clearly non-Darwinian account of
the origin of species and the explanation of trends (including an explicit coining of
the term "species selection" for explaining cladal patterns).
One might cite various truisms telling us that people ignorant of history will
be condemned to repeat its errors. But I would rather re-express this accurate and
rueful observation in a more positive manner by illustrating the power of historical
analysis to aid both our current understanding and the depth of our appreciation for
the intellectual importance of our enterprise. Finally, and to loosen the rein on
personal bravado that I usually try to hold at least somewhat in check, no scholar
should impose a project of this length upon his colleagues unless he believes that
some quirk of special skill or experience permits him to proceed in a unique
manner that may offer some insight to others. In my case, and only by history's
fortune of no immediate competition in a small field, I may be able to combine two
areas of professional competence not otherwise conjoined among current
evolutionists. I am not a credentialed historian of science, but I believe that I have
done sufficient work in this field (with sufficient understanding of the difference
between the Whiggish dilettantism of most enthusiastic amateurs, and the rigorous
methods applied by serious scholars) to qualify as adequately knowledgeable. (At
least I can read all the major works in their original languages, and I stay close to
the "internalist" style of analysis that people who understand the logic and history
of theories, but cannot claim truly professional expertise in the "externalist" factors
of general social and historical context, can usefully pursue.) Meanwhile I am, for
my sins, a lifelong and active professional paleontologist, a commitment that began
at age five as love at first sight with a dinosaur skeleton.
Many historians possess deeper knowledge and understanding of their
immediate subject than I could ever hope to acquire, but none enjoy enough in-
Defining and Revising the Structure of Evolutionary Theory 37