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

284 BULLY FOR BRONTOSAURUS Punctuated Equilibrium: A Hopeful Monster 285
mention in the first paper of any radical theory of speciation or mutation. But
later, about 1980, Gould decided that punctuated equilibrium was a
revolutionary idea after all—not an explanation of the lack of gradualism in
the fossil record, but a refutation of Darwinian gradualism itself. This claim
was advertised as revolutionary—and now it truly was. It was too revolutionary,
and it was hooted down with the same sort of ferocity the establishment
reserves for heretics like Elaine Morgan. Gould backpedaled hard,
offering repeated denials that he had ever meant anything so outrageous. In
that case, responded the establishment, there is after all nothing new in what
you say. But wait. Might there be still another reading of the hypothesis,
according to which it is both true and new? There might be. Phase three is
still under way, and the jury is out, considering several different— but all
nonrevolutionary—alternatives. We will have to retrace the phases to see
what the hue and cry has been about.
As Gould and Eldredge have themselves pointed out, there was an obvious
problem of scale in such diagrams as figure 10.6. What if we zoomed way in
on the orthodox picture and found that, once we enlarged it sufficiently, it
looked like this:
FIGURE 10.7
At some level of magnification, any evolutionary ramp must look like a
staircase. Is figure 10.7 a picture of punctuated equilibrium? If it is, then
orthodox Darwinism was already a theory of punctuated equilibrium. Even
paleontological data. If new species arise very rapidly in small, peripherally isolated local
populations, then the great expectation of insensibly graded fossil sequences is a chimera"
(Eldredge and Gould 1972, p. 82).
the most extreme gradualist can allow that evolution could take a breather for
a while, letting the vertical lines extend indefinitely through time until some
new selection pressure somehow arose. During this period of stasis, selection
pressure would be conservative, keeping the design roughly constant by
swiftly eliminating any experimental alternatives that arose. As the old
mechanic said, "Don't fix what isn't broke." Whenever a new selection
pressure arose, we'd see a "sudden" response of heightened evolution, a
punctuation interrupting the equilibrium. Was there really a revolutionary
point of disagreement being offered by Eldredge and Gould here, or were
they merely offering an interesting observation about the variability in tempo
of evolutionary processes and its predictable effects on the fossil record?
Punctuationists typically draw the punctuation parts of their revolutionary
diagrams absolutely horizontal (to make strikingly clear that they are
presenting a true alternative to the rampant ramp-view of orthodoxy). This
makes it look as if each of the design revisions illustrated takes place in a
twinkling, in no time at all. But that is just a misleading artifact of the huge
vertical scale adopted, which shows millions of years to the inch. The
sideways motion is not really instantaneous. It is only "geologically instantaneous."
An isolated population may take a thousand years to speciate, and its
transformation would therefore appear glacially slow if measured by the
irrelevant scale of our personal lives. But a thousand years, appropriately
recorded in geological time, is only an unresolvable moment, usually preserved
on a single bedding plane [in fossil-bearing rock], in a lifetime of
species that often live for several million years in stasis. [Gould 1992a, pp.
12-14.]
So suppose we zoom in on one of these thousand-year instants, changing
the vertical scale of the time dimension by a few orders of magnitude to see
what might actually be going on (figure 10.8). The horizontal step taken
between time t and time t' will have to be stretched out somehow, and we
must turn it into relatively big steps or little steps or tiny steps, or some
combination thereof.
Were any of the possibilities revolutionary? What exactly were Eldredge
and Gould maintaining? Here their respective views diverged somewhat, at
least for a while. The view was revolutionary, Gould claimed, because it
maintained that the punctuations were not just business-as-usual evolution,
not just gradual changes. Remember the old joke about the drunk who falls
down the elevator shaft and says, on rising, "Look out for the first step—it's a
doozy!"? For a while, Gould was proposing that the first step in the establishment
of any new species was a doozy—a non-Darwinian saltation
("somersault" and "saute" come from the same Latin root):