474 THE STRUCTURE OF EVOLUTIONARY THEORY
transmitted very far to other wedges in many lines of direction: beneath the
surface we may suppose that there lies a hard layer, fluctuating in its level,
and which may represent the minimum amount of food required by each
living being, and which layer will be impenetrable by the sharpest wedge.In this exigent world of intense and ubiquitous competition, severity of
struggle will be directly proportional to degree of relationship—most intense
among members of the same species, strong between individuals of closely related
species, and generally tapering with genealogical distance (and ecological
dissimilarity). As a result, new species tend to eliminate their ancestors and closest
relatives: "Each new variety or species, during the progress of its formation, will
generally press hardest on its nearest kindred, and tend to exterminate them" (1859,
p. 110).
Extinction therefore becomes a consequence of failure in biotic struggle, for
ecosystems generally stand chock full, and new wedges must be poised to make
their move whenever a chink appears. All species become enmeshed in a perpetual
upward spiral, running continuously just to keep pace with their fellows—the Red
Queen hypothesis (Van Valen, 1973): "For as all organic beings are striving, it
may be said, to seize on each place in the economy of Nature, if any one species
does not become modified and improved in a corresponding degree with its
competitors, it will soon be exterminated" (1859, p. 102).
The geological extension of wedging
If wedging rules the moment in a crowded world, then the extension of wedging
through time should build patterns of origination and extinction in the fossil record.
Following the dictates of the wedge, Darwin presents extinction as gradual and
natural—not as rapid elimination in the wake of environmental catastrophe, but as
slow diminution in the face of competition from "superior" forms, usually of close
genealogical relationship (see Chapter 12, pp. 1296-1303, for a further
development of this argument). Darwin chides us for ever regarding extinction as
unusual, and draws an analogy to the inevitability of death, usually following a
gradual course of prolonged weakening: "I may repeat what I published in 1845,
namely, that to admit that species generally become rare before they become
extinct—to feel no surprise at the rarity of a species, and yet to marvel greatly
when it ceases to exist, is much the same as to admit that sickness in the individual
is the forerunner of death—to feel no surprise at sickness, but when the sick man
dies, to wonder and to suspect that he died by some unknown deed of violence" (p.
320).
Darwin counterposes this view of extinction as gradual failure in biotic
competition to the alternative that both he and Lyell so strongly rejected—
catastrophic global paroxysm and resulting mass extirpation: "On the theory of
natural selection the extinction of old forms and the production of new and
improved forms are intimately connected together. The old notion of all