Darwin's Dangerous Idea - Evolution and the Meaning of Life

290 BULLY FOR BRONTOSAURUS
but only represents the proper scaling of ordinary events into the vastness of
geological time" (Gould 1992b, p. 12).
So this was a false-alarm revolution that was largely if not entirely in the
eyes of the beholders. But in that case, the view we find Gould and Eldredge
maintaining once we zoom in beyond the misleading time-squashing of their
geological diagrams, is not the rightmost doozy in figure 10.8 after all, but
one of the other, gradual, nonviolent paths illustrated. As Dawkins has noted,
the way in which Eldredge and Gould challenged "gradualism" was not, in
the end, by positing some exciting new nongradualism, but by saying that
evolution, when it occurred, was indeed gradual—but most of the time it was
not even gradual; it was at a dead stop. The lefthand diagram in figure 10.6 is
supposed to represent orthodoxy, but the feature of it that their theory
challenged was not its gradualism—once we get the scale right, they are
gradualists themselves. The feature they were challenging was what Dawkins
(1986a, p. 244) calls "constant speedism."
Now, has neo-Darwinian orthodoxy ever been committed to constant
speedism? In their original paper, Eldredge and Gould claimed that paleontologists
were mistaken in thinking that orthodoxy required constant speedism.
Was Darwin himself a constant speedist? Darwin often, and correctly,
harped on the claim that evolution could only be gradual (at best, you might
say). As Dawkins (1986a, p. 145) says, "For Darwin, any evolution that had
to be helped over the jumps by God was not evolution at all. It made a
nonsense of the central point of evolution. In the light of this, it is easy to see
why Darwin constantly reiterated the gradualness of evolution." But
documentary evidence in support of the claim that he was committed to
constant speedism is not just hard to find; there is a famous passage in which
Darwin clearly expresses the opposite view, the view that could be called—in
two words—punctuated equilibrium:
Many species once formed never undergo any further change ...; and the
periods, during which species have undergone modification, though long
as measured by years, have probably been short in comparison with the
periods during which they retain the same form. [Origin, 4th and subsequent
eds; see Peckham 1959, p. 727.]
Ironically, however, Darwin put just one diagram in Origin, and it happens to
show steadily sloping ramps. Steven Stanley, another major exponent of
punctuated equilibrium, reprints this diagram in his book (Stanley 1981, p.
36) and makes the inference explicit in his caption.
One effect of such claims is that today there is undoubtedly a tradition
imputing constant speedism either to Darwin himself or to neo-Darwinian
orthodoxy. For instance, Colin Tudge, a good science journalist, writing
about Elizabeth Vrba's recent claims concerning the pulse of evolution,
Punctuated Equilibrium: A Hopeful Monster 291
The tree of life published by Darwin in the Origin (1859, p. 117). The tree depicts
a gradualistic pattern of evolution. Each fanlike pattern represents the slow evolutionary
divergence of populations. Darwin believed that new species, and eventually
new genera and families, formed by this kind of slow divergence. [Stanley 1981.]
FIGURE 10.9
points to the presumed implications for orthodoxy of current research on the
evolution of impalas and leopards:
Traditional Darwinism would predict a steady modification of the impala
over 3 million years, even without climatic change, because it still needs
to outrun leopards. But, in fact, neither impalas nor leopards have changed
very much. They are both too versatile to be worried by climatic change,
and competition between them and with their own kind does not—as
Darwin supposed—provide sufficient selective pressure to cause them to
alter. [Tudge 1993, p. 35.]
Tudge's presumption that the discovery of three million years of stasis in the
impala and leopard would confound Darwin is a familiar one, but it is an
artifact, direct or indirect, of a particular forced reading of the "ramps" in
Darwin's (and other orthodox) diagrams.
Gould has proclaimed the death of gradualism, but is he himself, then, a
gradualist (but not a constant speedist) after all? His denial that his theory
proposes any "violent mechanism" suggests that he is, but it is hard to tell,
for on the very same page he says that, according to the theory of punctuated
equilibrium,