Seeds of Hierarchy 237
of his theory as a consequence of ordinary natural selection at the organismic
level?
I have proceeded in this way for a simple reason: Darwin's argument doesn't
work, and he came to recognize this failure in the face of his brave attempt. Darwin
struggled mightily to render this second keystone of his full theory by natural
selection alone, but he could not carry the logic to completion. He failed because
his full argument demands a major contribution from species level selection (or, at
the very least, strong attention to explicit sorting at the species level). I don't know
that Darwin ever grasped this need in a fully explicit way, committed as he was to
the exclusivity of selection on organisms. But he recognized the crucial difficulty
at several places in his exposition; and, with his usual honesty, he made his distress
palpable again and again.
I perceive his discomfort in the labored description of divergence given in the
Origin—15 pages for a few points repeated many times, first in one way, then in
another, all in a book so compressed that Darwin wanted to include the word
"abstract" in the title. (John Murray, his publisher, demurred on obvious practical
grounds). I sense Darwin's malaise in the fact that for this concept alone (among all
the complex ideas developed in the Origin) he supplied both a figure and a
meticulous "caption" (as it were), running for nearly ten pages. I note his
dissatisfaction in the frequent shifting of attribution within his text—from
consequences of organismic struggle (his usual and distinctive argument) on the
one hand, to advantages for higher level units (usually species) on the other. In my
reading, these shifts cannot be interpreted as comfortable transitions rooted in a
confident reduction of higher level phenomenology to lower level causality (as he
had achieved in explaining adaptation by natural selection), but must instead be
regarded as genuine gropings and confusions. Finally, Darwin recorded his distress
in explicit exclamations of doubt—from his "I must think out [this] last
proposition" of the 1855 note, to his description of divergence as "this rather
perplexing subject" in the Origin (1859, p. 116).
If the founder of the non-hierarchical organismal view, this doggedly
persistent, fiercely honest and brilliant thinker, tried so hard to make the canonical
argument of natural selection work for the central higher-level phenomenon of
species diversity—and could not bring the logic of his argument to a satisfactory
completion—then perhaps his failure tells us something about the necessity of
hierarchical selection. Darwin, by his own formulation, faced two great issues—
adaptation and diversity. He tried to render both by natural selection based on
struggle among organisms—adaptation by the Malthusian insight of 1838,
diversity by the principle of divergence formulated in the mid 1850's. His
explanation worked well, or at least sprung no logical holes, for adaptation. But he
could not carry the same argument through, despite extensive and valiant attempts,
for diversity—the primary domain of species selection, as all modern advocates
hold (see, for example, Gould and Eldredge, 1988, replying to Maynard Smith's
1988 misconception).
Schweber (1980,1985,1988) noted Darwin's trouble with discordance between