164 THE STRUCTURE OF EVOLUTIONARY THEORY
Darwinism embodies a meaningful central logic, or "essence," and that other
proposals about evolutionary mechanisms can be classified with reference to their
consonance or dissonance with these basic Darwinian commitments.
I was particularly pleased to learn that Kellogg's categories, though differently
named and parsed, are identical with those recognized here. He divides the
plethora of proposals under discussion in his time into those "auxiliary to" and
those "alternative to" natural selection. Among auxiliaries that aid, expand,
improve, or lie within the spirit of Darwinism, Kellogg highlights two principal
themes: studies of Wagner, Jordan, and Gulick on the role of isolation in the
formation of species; and hierarchical models of selection as espoused by Roux
and Weismann (discussed in detail in Chapter 3). I noted with special gratification
that Kellogg recognized hierarchy as an auxiliary, not a confutation, to Darwinism,
for this same contention sets a principal theme of this book.
In his second category of confutations, Kellogg identified "three general
theories, or groups of theories, which are offered more as alternative and
substitionary theories for natural selection than as auxiliary or supporting theories"
(1907, p. 262): Lamarckism (inheritance of acquired characters in the form
advocated by late 19th century neo-Lamarckians), orthogenesis, and heterogenesis
(Kellogg's designation for saltationism).
Kellogg's taxonomy works particularly well in evaluating the central
principles of Darwinism. His "auxiliaries" aid selection (by addition of other
principles that do not challenge or diminish selection, or by expansion of selection
to other levels); but his "alternatives" confute particular maxims of the minimal
commitments for Darwinian logic. The Kelloggian "alternatives" all deny the
fundamental postulate of creativity for selection by designating other causes as
originators of evolutionary novelties, and by relegating selection to a diminished
status as a negative force. Each alternative rejects a necessary Darwinian postulate
about the nature of variation (see pp. 141— 146): Lamarckism and orthogenesis
deny the principle of undirected variability; saltationism refutes the claim that
variation must be small in extent.
I warmly endorse Kellogg's approach. As practicing scientists, we often do
not pay enough respect to the logical structure of an argument—to its rigors and its
entailments. We tend to assume that conclusions flow unambiguously from data,
and that if we observe nature closely enough, and experiment with sufficient care
and cleverness, the right ideas will somehow coalesce or flow into place by
themselves. But scholars should know, from the bones and guts of their practice,
that all great theories originate by intense and explicit mental struggle as well. We
should not castigate such efforts as "speculation" or "armchair theorizing"—for
mental struggle deserves this designation only when the thinker opposes or
disparages our shared conviction that, ultimately, empirical work or testing must
accompany and validate such exercises in thought (and then all scientists would
agree to let the calumny fall). Great theories emerge by titration of this basically
lonely mental struggle with the more public, empirical acts of fieldwork and bench
work.
One need look no further than Charles Darwin for proper inspiration. He