Seeds of Hierarchy 239
imply and grade into the other; the two levels could represent alternate solutions of
the Necker cube (see Dawkins, 1982)—that is, views of the same configuration
from different vantage points. The individual success of extreme organisms may
simply imply, ipso facto and necessarily, the ultimate multiplication of species, and
success measured by number of descendant taxa might therefore act as a surrogate
for, or simple extension of, natural selection. (For this reason, I assume, Darwin
includes the principle of divergence as the largest section of chapter 4, entitled
natural selection.)
But this argument does not cohere, and I think that any careful reader must be
struck by Darwin's discomfort as he mixes and juggles the argument for success of
extreme organismal variants with the calculus of advantage mapped by number of
descendant taxa. Darwin's argument falters because the use of a lower level
(success of extreme variants, in this case) to explain a phenomenon at a higher
level (multiplication of species) can only work if "perfect transfer" can be
defended—that is, if the lower level entails the higher as a direct consequence
without any intervention (even a synergistic boost, not to mention a contrary force)
from causes at the higher level itself. Darwin understood this principle perfectly
well. Indeed, he was probably the only man who, in this infancy of evolutionary
science, had carefully and consistently thought the logic of selection through to this
correct interpretation. Thus, Darwin tried to construct an argument for perfect
transfer—but he failed. Darwin advanced these claims in Natural Selection, but
ultimately dropped them from the Origin, because (I suspect) he recognized their
weaknesses. (I criticize the arguments for perfect transfer in points two and three
below; in this subsection, I document Darwin's bold claim for a higher level
calculus of individual success.)
Consider Darwin's first hypothetical example of the principle of divergence in
the Origin (1859, p. 113). He speaks of a "carnivorous quadruped" that, by
ordinary natural selection, has expanded in population to the limits of local
environments. To do even better in the struggle for life, this form must now
diversify into several descendant taxa. But how can the canonical argument for
natural selection be cashed out in terms of multiplicity of descendant species? The
logic of individual struggle carries no implications about the splitting of
populations (especially for an in situ sympatric splitting that implies general
predictability rather than the simple good fortune of geographic isolation).
Take the case of a carnivorous quadruped, of which the number that can be
supported in any country has long ago arrived at its full average. If its
natural powers of increase be allowed to act, it can succeed in increasing
(the country not undergoing any change in its conditions) only by its
varying descendants seizing on places at present occupied by other animals:
some of them, for instance, being enabled to feed on new kinds of prey,
either dead or alive; some inhabiting new stations, climbing trees,
frequenting water, and some perhaps becoming less carnivorous. The