492 THE STRUCTURE OF EVOLUTIONARY THEORY
Geology, which the future historian will recognize as having produced a revolution
in natural science, yet does not admit how incomprehensibly vast have been the
past periods of time, may at once close this volume" (1859, p. 282). Of course, we
now acknowledge the immensity of time and therefore continue to open the Origin.
We also dismiss Cuvier's argument that lack of recorded intermediacy precludes
evolution.
But Cuvier's claim retains force in a more restricted sense: the earth's
measured history does not provide enough time to dissolve the appearance of mass
extinction into gradual change masked by an imperfect record. Geology therefore
does run "too fast" to explain these crucial episodes by extended gradualism
through an imperfect record—and if catastrophic mass extinctions are, as many
paleontologists now argue (see Chapter 12), more frequent, profound, rapid, and
different in their effects than we had previously admitted, then natural selection in
Darwin's accumulative mode, with biotic competition as a primary source of order,
may become seriously demoted in relative frequency among the causes of
macroevolutionary pattern. In this sense, the pace of geological change remains a
vital subject for evolutionary theory, and Cuvier's last line still sounds a valid
warning. For evolutionists committed to biotic competition by wedging as the
primary source of macro-evolutionary pattern, new data on mass extinction may
"not leave sufficient time for the production of the changes that are alleged to have
taken place."
Fortunately, we may proceed beyond conjecture in trying to discern Darwin's
personal response to geological systems that threatened the efficacy of natural
selection as an adequate source for the larger pattern of life's history. Cuvier died
while Darwin worked on the Beagle and Lyell thrust his metaphorical sword (at
least to Darwin's satisfaction) through the heart of traditional catastrophism. But
Darwin could not rest easy, in full confidence that geological change would always
plod along at optimal slowness for natural selection. For a formidable challenge,
similar in broad concept to Cuvier's but very different in overt claims, greatly
worried Darwin during the last fifteen years of his life—the "odious spectre" of
Lord Kelvin. Darwin's widely misunderstood response proves, once again, how
clearly he had pondered and assimilated the logic of his theory—and how much he
required the slowness and uniformity of geological change.
Darwin's Geological Need and Kelvin's Odious Spectre
The familiar story of Lord Kelvin's incursion into geology has usually been
recounted as a morality play. In basic outline, arrogant physics invades, but
beleaguered natural history holds the line and triumphs, ultimately in a twist of
delicious irony. I won't dispute this basic outline, but an attention to detail does
compromise the traditional moral message, while also providing a striking example
of Darwin's geological commitments.
In 1866, William Thomson, the future Lord Kelvin, published one of the most
arrogant documents in the history of science—a one-paragraph paper (with an
appended calculation) boldly entitled "The 'Doctrine of Uniformity'