Tiers of Time and Trials of Extrapolationism 1299
argument that Darwin had so carefully devised (see Chapter 6, pp. 467-479) to
validate something more particular but no less important: his culture's central belief
in progress, especially when Darwin had so increased the difficulty of the problem by
constructing a theory (natural selection itself) that could not render this
consummately desired result through its bare-bones mechanics. (For this reason, I
discuss mass extinction in this relatively short Chapter 12, conceived as a counterpart
to the equally brief Chapter 6 of this book's historical half—for these chapters feature
the surrogate geological defenses of extrapolation, rather than the arguments from
biological theory inherent in the first two legs of Darwin's logical tripod, and treated
in extenso in Chapters 3-5 of the historical half, and 8-11 of this second half on
contemporary debates.)
To explain the general pattern of life's history, Darwin sought to extrapolate the
results of competition ordained by the immediacies of natural selection in ecological
moments. In particular (as discussed and documented in Chapter 6, pp. 467-479), he
used his "metaphor of the wedge" to argue that most competition, in a world chock
full of species, unfolds in the biotic mode of direct battle for limited resources, mano
a mano so to speak, and not in the abiotic mode of struggle to survive in difficult
physical conditions. If struggle by overt battle (which favors mental and
biomechanical improvement) trumps struggle against inclement environment (which
often favors cooperation rather than battle and usually leads, in any case, to
specialized local adaptation rather than to general improvement), then a broad vector
of progress should pervade the history of life.
These two geological chapters (9 and 10) include nearly all of Darwin's passages
and notable arguments for linking general progress to the extrapolation of momentary
biotic competition through geological time. "The theory of natural selection is
grounded on the belief that each new variety, and ultimately each new species, is
produced and maintained by having some advantage over those with which it comes
into competition; and the consequent extinction of less-favored forms almost
inevitably follows" (p. 320). Or consider this passage, with multiple metaphors of
victory and defeat: "In one particular sense the more recent forms must, on my
theory, be higher than the more ancient; for each new species is formed by having
had some advantage in the struggle for life over other and preceding forms ... I do not
doubt that this process of improvement has affected in a marked and sensible manner
the organisation of the more recent and victorious forms of life, in comparison with
the ancient and beaten forms" (pp. 336-337). Most famously, Darwin writes in the
summary of both chapters (p. 345): "The inhabitants of each successive period in the
world's history have beaten their predecessors in the race for life, and are, in so far,
higher in the scale of nature; and this may account for that vague yet ill-defined
sentiment, felt by many paleontologists, that organisation on the whole has
progressed."
To bring the literal appearance of mass extinction back under the rubric of
extrapolation, Darwin realizes that he does not have to deny episodes of