The Essence of Darwinism and the Basis of Modern Orthodoxy 129
Darwin raises two separate challenges to natural selection for the case of
sterile castes in the Hymenoptera. How, first of all, can sterile castes evolve
adaptive differences from queens (and from each other), when individuals of these
castes cannot reproduce? If non-reproductive organisms can evolve adaptations,
mustn't selection then be working at the higher level of colonies as wholes?
Darwin answers, by analogy to domesticated animals once again, that differential
survival of non-reproductives may still record selection on fertile members of the
population. After all, a breeder can improve the distinct form of castrated animals
(raised for food or labor), by mating only those fertile individuals that sire non-
reproductives with the most advantageous traits (as recognized by the correlation
of selectable features in parents with different traits in their castrated offspring):
I have such faith in the powers of selection, that I do not doubt that a breed
of cattle, always yielding oxen with extraordinarily long horns, could be
slowly formed by carefully watching which individual bulls and cows,
when matched, produced oxen with the longest horns; and yet no one ox
could ever have propagated its kind. Thus I believe it has been with social
insects: a slight modification of structure, or instinct, correlated with the
sterile condition of certain members of the community, has been
advantageous to the community: consequently the fertile males and females
of the same community flourished, and transmitted to their fertile offspring
a tendency to produce sterile members having the same modification. And I
believe that this process has been repeated, until that prodigious amount of
difference between the fertile and sterile females of the same species has
been produced, which we see in many social insects (p. 238).
(This quotation illustrates a common source of misunderstanding. Darwin
does often use such phrases as "advantageous to the community." By our later
linguistic conventions, such a statement might seem to signify a leaning to group
selectionist arguments. But these conventions did not exist in Darwin's generation.
Note how he uses this phrase only as a description of a result. Darwin identifies the
causal process yielding this result, in this case and almost every other time he
invokes such language, as selection on organisms, with benefit to communities as
an epiphenomenal effect.)
The second challenge, the origin of sterility itself, seems more serious—for
how could selection, especially in its necessarily gradualistic mode, promote the
diminution of reproductive power in individuals? Clearly, the increasingly sterile
workers cannot be promoting their own fitness; but their labor may aid their entire
nest or hive. Must not the evolution of sterility therefore provide prima facie
Species Selection The Failure of Darwin's Argument and the Need for
exclusivity of selection on organisms?
Darwin does indeed refer to sterility as "one special difficulty, which at first
appeared to me insuperable, and actually fatal to my whole theory" (p. 236). He
then offers an explanation, based exclusively on organismal selection and similar
to his argument about differences in form between workers and