234 THE STRUCTURE OF EVOLUTIONARY THEORY
DIVERGENCE AS A CONSEQUENCE OF NATURAL SELECTIONIn Chapter 2,1 noted the radical character and intellectual power of Darwin's
primary argument as embedded in the Malthusian insight about natural selection.
In an irony that overturned the entire tradition of natural theology, Darwin held
that all the higher order "harmonies" of good design and ecological balance arose
as side consequences of a process—struggle among organisms for personal
reproductive success—that would demand an opposite interpretation if we sought
moral messages in nature. Now, in the mid 1850's, Darwin attempted the same
philosophical coup to accomplish for diversity exactly what he had done for
adaptation in the initial formulation of natural selection—that is, to render a higher
level "good," the maximization of life through division of labor, as a side
consequence of organismic struggle. In January 1855 (in the note that Schweber
views as the genesis of the principle of divergence), Darwin takes this fateful
repeat step into the philosophical radicalism of rendering higher harmonies by
individual struggle (quoted in Schweber, 1988): "On Theory of Descent, a
divergence is implied and I think diversity of structure supporting more life is thus
implied ... I have been led to this by looking at heath thickly clothed by heather and
a fertile meadow both crowded, yet one cannot doubt more life supported in
second than in the first; and hence (in part) more animals are supported. This is the
final cause but mere result from struggle (I must think out last proposition)."
Darwin's abysmal handwriting causes endless trouble for scholars. All historians have
recognized the crucial status of this final sentence, but each major exegete reads the line in a
different way. Ospovat (1981, pp. 180-181) offers the following interpretation: "This is not
final cause, but mere results from struggle, (I must think out this last proposition.)" Browne's
version (1980, p. 71) reads: "This is not final cause but mere result from struggle (I must
think out this last proposition.)" And Kohn (1985, p. 256) offers this deciphering: "This is
not final cause, but more [a] result from struggle, (I must think out this last proposition.)"
Aside from minor points of articles and punctuation, two disagreements are potentially
substantial: First, did Darwin write "mere" or "more" with respect to struggle? "Mere" would
be stronger, for then the higher order harmony of ecosystems becomes nothing but a
consequence. But "more" still conveys the same sense—for higher order maximization of life
would still represent more a consequence of individual struggle than anything else. Second,
did Darwin say that maximization is not a final cause (Ospovat, Browne, Kohn), or does he
choose to view such abundance of life as the final cause of struggle (Schweber)? These
different readings seem to suggest a serious discrepancy, but, in fact, the meaning will be
much the same in either case. For Darwin tells us, one way or the other, that individual
struggle provides the generating cause, with maximization of life arising as a consequence.
Thus, Darwin argues either that Aristotle's notion of "final cause" ("purpose" in the
vernacular) has no place in science (since maximization of life only represents a result of
struggle); or he states that we may continue to use the term "final cause" in an informal
sense, so long as we acknowledge the underlying mechanism, or efficient cause, producing
the phenomenon. (We may, in this case, view maximization as a "final cause" so long as we
recognize its origin in struggle, and not in created harmony.) The same terminological
ambiguity continues today in evolutionary theory. We use the language of final cause, or
purpose, in describing adaptation, if only because we do not wish to abandon ordinary
language. We say that giraffes evolved long necks "in order to" eat high foliage. But we
recognize the causal basis of such adaptive "purpose" in natural selection by unconscious
organismic struggle.