94 THE STRUCTURE OF EVOLUTIONARY THEORY
genius, took this secondary force, proposed a new mechanism for its operation
(natural selection), and then redefined this former source for superficial tinkering
as fully sufficient to render all of evolution—thus branding the separate and more
exalted force of progress as illusory.
Such an argument poses an obvious logical dilemma: how can such power be
granted to a force formerly viewed as so inconsequential? After all, evolution must
still construct the full pageant of life's history and the entire taxonomic panorama,
even if we abandon the concept of linear order. Darwin's answer records the depth
of his debt to Lyell, the man more responsible than any other for shaping Darwin's
basic view of nature. Time, just time! (provided that the "inconsequential" force of
adaptation can work without limit, accumulating its tiny effects through geological
immensity). The theory's full richness cannot be exhausted by the common
statement that Darwinism presents a biological version of the "uniformitarianism"
championed by Lyell for geology, but I cannot think of a more accurate or more
encompassing one-liner. (In a revealing letter to Leonard Horner, written in 1844,
Darwin exclaimed: "I always feel as if my books came half out of Lyell's brains ...
for I have always thought that the great merit of the Principles [of Geology], was
that it altered the whole tone of one's mind and therefore that when seeing a thing
never seen by Lyell, one yet saw it partially through his eyes" (cited in Darwin,
1987, p. 55).)
Darwin, in his struggle to formulate an evolutionary mechanism during his
annus mirabilis (actually a bit more than two years) between the docking of the
Beagle and the Malthusian insight of late 1838, had embraced, but ultimately
rejected, a variety of contrary theories—including saltation, inherently adaptive
variation, and intrinsic senescence of species (see Gruber and Barrett, 1974; Kohn,
1980). A common thread unites all these abandoned approaches: for they all
postulate an internal drive based either on large pushes from variation
(saltationism) or on inherent directionality of change. Most use ontogenetic
metaphors, and make evolution as inevitable and as purposeful as development.
Natural selection, by contrast, relies entirely upon small, isotropic, nondirectional
variation as raw material, and views extensive transformation as the accumulation
of tiny changes wrought by struggle between organisms and their (largely biotic)
environment. Trial and error, one step at a time, becomes the central metaphor of
Darwinism.
This theme of relentless accumulation of tiny changes through immense time,
the uniformitarian doctrine of Charles Lyell, served as Darwin's touchstone
throughout his intellectual life. Uniformitarianism provides the key to his first
scientific book (Darwin, 1842) on the formation of coral atolls by gradual
subsidence of oceanic islands, long continued. And the same theme defines the
central subject of his parting shot (1881), a book on the formation of vegetable
mould by earthworms. Darwin, for lifelong reasons of personal style, did not
choose to write a summary or confessional in lofty philosophical terms, but he did
want to make an exit with guns blazing on his favorite topic. Ironically, Darwin's
overt subject of worms has led to a common interpretation quite opposite to his
own intent—his misrepresentation as a doddering old naturalist who couldn't judge