544 THE STRUCTURE OF EVOLUTIONARY THEORY
then, following this book's focal argument that the minimal commitments of
Darwinian logic encompass three central themes, the other two legs of this
essential tripod should experience corresponding changes as the Synthesis
hardened. I will not provide so extensive a discussion of these other legs—levels of
selection and extrapolation into geological time—but I do wish to record that the
literature of these subjects also experienced the same ontogeny of solidification
(and unjustified neglect of reasonable alternatives).
LEVELS OF SELECTION
Darwin, as we have seen (pp. 125-137), viewed organisms as nearly exclusive
agents of selection—for deep reasons situated at the core of both the logic (the
invisible hand of Adam Smith transferred to nature) and the psychology (the
inversion of Paley's world) of his theory. But few Darwinians grasped the rationale
or centrality of this principle, and a tradition of vagueness and loose thinking about
levels of selection developed. Some, like R. A. Fisher, rode Darwin's wave and
wrote explicitly and cogently about reasons for choosing individual organisms as
the proper locus, and for disregarding, as effectively impotent, other levels that
must be deemed conceivable in theory (1958, on species selection—see my
critique of Fisher on pp. 644-652). But others, dating back to A. R. Wallace
himself (see pp. 131-132), never understood the full logic and implications of this
issue, and ranged indiscriminately up and down potential levels, without grasping
the theoretical problems entailed by such excursions.
Thus, a fluid situation prevailed on this issue at the time of the Darwinian
centennial celebrations of 1959—my point of reference for the triumphal height of
the Modern Synthesis in its strongly adaptationist version. Adaptation had become
all the rage, but vagueness shrouded the key issue of selection's focus and level—
and for two reasons.
First, and less important because the position attracted few supporters, a few
evolutionists explicitly advocated a multi-level view of both selection and
adaptation. A group of Chicago ecologists, authors of an important textbook
known by its acronym of AEPPS (Allee, Emerson, Park, Park and Schmidt,
Principles of Animal Ecology, 1949), generated and led this small movement.
Emerson spoke at the Chicago centennial symposium, and presented his multilevel
view in both content and title: "The evolution of adaptation in population systems."
Emerson begins by acknowledging the conventional Darwinian preference for
individual organisms (and reminding us that he will not neglect this usual
argument). But he then stakes his higher claim: "It is my intention in this essay to
emphasize the evolution of adaptation in population systems without, however,
negating the data or the major interpretations of the roles of individuals in
evolutionary history or processes" (1960, p. 307).
I find Emerson's article frustrating, for his arguments are so reasonable in
some places, and so very wrong, to the point of illogic, in others. On the one hand,
he presents a defendable and properly philosophical criterion for