392 THE STRUCTURE OF EVOLUTIONARY THEORY
Whitman's attitude towards natural selection bears closer scrutiny as an aid
(still useful today) for clarifying the borderline between two intergrading yet
contradictory strategies: (1), using the structuralist and formalist concept of
channels in pluralistic reinforcement with natural selection to forge helpful
revisions of basic Darwinian theory (the position advocated in this book); or (2)
viewing channels as so deep, so unidirectional, and so limiting that such
constraints impel evolutionary change from within, leaving selection only to tinker
with minor details (a truly anti-Darwinian theory that led the Modern Synthesis to
reject orthogenesis completely). I cannot place Whitman on either end of this
continuum—for he argued both sides and usually rested with ambivalence at some
middle position. But his writings provide our best illustration of this important
concept in the logic and historiography of theories.
Whitman's usual account of natural selection grants a distinctly subsidiary
role to Darwin's process. By adaptation's dumb luck, the inexorable process of
reduction in color may occasionally generate a form with utility. At this point,
natural selection may intervene to tinker, rearrange, and even strengthen the valued
colors. But selection cannot long prevail, for even a useful concentration of color
must eventually move towards orthogenetic effacement: "Even in cases where
natural selection has probably played a conspicuous part in modifying and
beautifying these marks ... we find that the reducing process has not been brought
to a standstill" (1919, p. 62).
Whitman asks us to consider examples from both major components of
color—bars and checkers: The bars may be useful as marks of recognition, but
they arise by orthogenetic reduction, not natural selection, and Darwinian forces
cannot maintain them against the stronger internal push to effacement. (Note the
interesting admission at the end of this statement that we have yet to fathom the
mechanism of a process powerful enough to overcome selection.)
Standing alone on a pale gray ground, these bars would gain immensely in
conspicuity [sic] and utility as ornamental recognition marks. The
advantage of all this to the species, whatever it be, would be merely an
accident of the situation presented at this particular point in a progressive
series of modifications. It is conceivable that the utility of the bars might be
great enough to give natural selection a chance to step in and bar [pun
intended?] the way to further reduction. But the process of obliteration has
certainly gone much farther in many other species. There may be stages in
the process, which suggest utility; but when we consider the whole series of
stages and note that the process runs on, sweeping away the stages, which
we imagine to be most useful, we are left with the conviction that some
general principle underlying the course of events has not yet been fathomed
(1919, p. 61).Whitman stresses the same point, in even stronger form, for the few,
conspicuous and apparently adaptive checkers of mourning doves. These
remaining marks of color are "hanging tough," stubbornly resisting the
orthogenetic