1036 THE STRUCTURE OF EVOLUTIONARY THEORY
biology and paleontology," distinguishes the conventional statistical meaning from a
particular and distinctive sense frequently employed in Darwinian literature—
namely, "chance" defined as events occurring for reasons unrelated to the canonical
mechanism of natural selection. Eble writes (1999, p. 77): "The gist of the
evolutionary notion of chance is that events are independent of an organism's need
and of the direction provided by natural selection in the process of adaptation."
Eble discusses examples ranging widely across all scales of evolution, but we all
know (and we all make excuses for the resulting confusion in our lectures to
elementary courses) the most troubling and common case—the claim that mutational
variation in populations, the fuel of natural selection, is "random. " Of course, we
know perfectly well that such usage does not invoke the usual mathematical concept
of randomness, and that we only mean "unrelated to the direction of natural
selection"—a point emphasized in Chapter 2 in my discussion of Darwin's need for
isotropy in variation (see pp. 144-146). Eble (1999, p. 78) cites the acknowledgment
of many biologists, and the analyses of such leading philosophers as Popper and
Sober, of this almost "studied" confusion, including a quotation of my own statement
(Gould, 1982b, p. 386): "By 'random' in this context, evolutionists mean only that
variation is not inherently directed towards adaptation, not that all mutational changes
are equally likely."
(Eble recommends that we retain the words "chance" and "random" for both
meanings, and then enforce the separation with the restricting adjectives "statistical"
vs. "evolutionary" chance. He argues (p. 75) that "evolutionary studies... can benefit
from the simultaneous application of statistical and evolutionary notions of
chance"—defining the second concept as "independence from adaptation and the
directionality imposed by natural selection," a definition as clearly and explicitly
"theory-bound" as any I have ever read. I agree entirely with Eble's analysis. I dissent
only from his terminological decision to retain the word "chance" for both concepts,
and to rely upon moderating adjectives to enforce the distinction. I would prefer the
codification of a different name for the evolutionary meaning both because I don't
trust the power of subsidiary adjectives to clarify the vital distinction, and because the
statistical meaning represents such an important concept, in both science and
practical human life, that exclusivity of usage might aid our uphill battle to educate
people about the basic meaning of probability. But my terminological disagreement
with Eble does not detract from my admiration for his clear characterization of the
distinction, and his rich discussion of the largely unrecognized confusions thus
generated.)
In any case, Eble's characterization of evolutionary "chance," and his
documentation of such extensive usage in a sense so contrary to the basic mathe-
matical meaning of a fundamental term in science, only underscores the enormous
range and influence of natural selection as our canonical theory. If organismal
selection, and its key consequence of adaptation, have become so prototypical in
defining how evolution works, and what evolution does, that we usually designate
any other result as a "chance" phenomenon—even