had explicitly denied such an outcome as the most radical implication of his
theory), but on subsidiary ecological claims for the predominance of biotic over
abiotic competition, and for a geological history of plenitude in a persistently
crowded ecological world, where one species must displace another to gain entry
into ecosystems (the metaphor of the wedge). Darwin used these ecological
sequelae, along with the gradualist and incrementalist logic of natural selection
itself, as primary justifications for his third essential claim of selection's scope, or
the uniformitarian extension of small-scale microevolution, in a smoothly
continuationist manner, to explain all patterns of macro-evolution by accumulation
of increments through the immensity of geological time.
- Such a claim requires that the geological stage operate in an appropriate,
and "Goldilockean," manner—not too much change to debar the operation and
domination of this slowly and smoothly accumulative biological mode, and not too
little to provide insufficient impetus (within Darwin's externalist and functionalist
theory) for attributing the amount of change actually observed to natural selection. - The primary claim of "too much" derived from the school of
"catastrophism" in geology—a movement that has been unfairly stigmatized by
later history, following Lyell's successful and largely rhetorical mischaracterization
(he was a lawyer by profession), as an unscientific defense of super-naturalism to
cram the observed results of geology into the strictures of biblical chronology, but
that actually took the opposite position of strict empirical literalism (whereas
uniformitarians argued that the numerous literal appearances of rapidity in the
geological record must be "interpreted" as misleading consequences of how
gradual change must be expressed in a woefully imperfect set of strata). The great
catastrophist Cuvier, in particular, was an Enlightenment rationalist, not a
theological apologist—and he based his defense of catastrophism upon his literalist
reading of the paleontological and geological record. - The primary claim of "too little" geology followed Lord Kelvin's
increasingly diminished estimates for the age of the earth (incorrectly made—
although Kelvin accurately described the necessary, but (as it turned out)
empirically false, logic required to validate his views—by assuming that heat now
flowing from the earth represented a continuing loss from an originally molten
state). Darwin worried intensely over Kelvin's claims, even referring to him as an
"odious spectre" in a letter to Wallace. Darwin feared that Kelvin's low estimates
would not permit enough time to generate the history of fife under his slowly
acting theory of gradualistic and accumulative change. Although this story has
been told often, and has become familiar to scientists, an important (and decisive)
aspect of the tale has rarely been exposed: Darwin fought this battle alone, and his
strong distress illustrates the maximal, and unique, extent of his gradualistic and
continuationist commitments. His closest colleagues, Wallace and Huxley, did not
find Kelvin's low estimates unacceptable, but argued that we had only been led to
expect such slow change from our previous conception of the earth's age, and that
faster rates
70 THE STRUCTURE OF EVOLUTIONARY THEORY