Pattern and Progress on the Geological Stage 475
the inhabitants of the earth having been swept away at successive periods by
catastrophes, is very generally given up" (p. 317).
Darwin centers his second geological chapter ("On the succession of organic
beings," Chapter 10) upon an argument, framed in his usual mode of probing
behind the literal appearance of an imperfect record, for the prevalence of a pattern
that would validate gradual, biotically-driven extinction as a norm for the history
of clades. Darwin denies that much extinction occurs by simultaneous or
coordinated removal of unrelated forms. On the contrary, he argues, groups wane
slowly and individually as superior competitors wax, producing a distinctive
pattern of "megawedging" through geological time. "The extinction of old forms is
the almost inevitable consequence of the production of new forms" (p. 343). "As
new species in the course of time are formed through natural selection, others will
become rarer and rarer, and finally extinct. The forms which stand in closest
competition with those undergoing modification and improvement, will naturally
suffer most" (p. 110).
The validation of progress
For two reasons, Darwin could not find a rationale for progress in abiotic,
physically-driven extinction and adaptation: first, a non-directional vector of
environmental change can only elicit a set of meandering responses in the adaptive
adjustments of organisms; second, the more serious challenge of catastrophe and
mass extinction raises the specter of randomness and death for reasons unrelated to
the adaptive struggles of normal times—the wheel of fortune vs. the wedge of
progress (Gould, 1989d).
But victory over other creatures in an intense and unrelenting struggle for
limited resources does permit an inference about progress. Now species triumph
because, in some sense admittedly difficult to define, winners are "better" than the
forms they vanquish. And the more uniformitarian the larger picture—the more
that macroevolutionary pattern arises as a simple summation of immediate
struggles—so do we gain increasing confidence that replacement and extinction
must record the differential success of globally improved species. Thus, progress
becomes an ecological concept for Darwin—not a deduction from the inevitable
mechanics of natural selection, but a mode of operation for natural selection in a
particular kind of ecological world. If crowded habitats, where creatures must
struggle to the death for limited resources, represent an ecological norm on earth,
and if geological change usually proceeds at a sufficiently stately and unobtrusive
pace to permit the fruits of biotic competition to accumulate into patterns of
origination and extinction through time, then we may understand why
"organization on the whole has progressed" (p. 345). Darwin links all his
statements about progress firmly to his ecological theory of plenitude and to the
prevalence of biotic competition.
Consider Darwin's language and imagery ("inferior" forms "beaten" by
"victorious" relatives) as he presents his key argument for linking the gradual
geological decline of groups to the success of closely related competitors (a