126 THE STRUCTURE OF EVOLUTIONARY THEORY
of this chapter—must be resolved before we can understand the theory's basic
operation: the issues of agency and efficacy. The basic historical context of
selection—its discovery and utilization by Darwin as a refutation of Paleyan
natural theology through the imported causal structure of Adam Smith's invisible
hand—grants primacy to the issue of agency (therefore treated here in the first of
two sections on fundamental attributes). The rebuttal of the former centerpiece of
natural history—the belief that organic designs record the intentions of an
omnipotent creative power—rests upon the radical demotion of agency to a much
lower level, devoid of any prospect for conscious intent, or any "view" beyond the
immediate and personal. So Darwin reduced the locus of agency to the lowest level
that the science of his day could treat in a testable and operational way—the
organism (for ignorance of the mechanism of heredity precluded any possibility of
still further reduction to cellular or genie levels). The purely abstract statement of
natural selection (the syllogistic core) leaves the key question of agency entirely
unanswered. Selection may be in control, but on what does selection act? On the
subcellular components of heredity? on organisms? on populations? on species? or
on all these levels simultaneously?
Darwin grasped with great clarity what most of his contemporaries never
understood at all—that the question of agency, or levels of selection, lies at the
heart of evolutionary causation. And he provided, from the depth of his personal
convictions, the roots of his central premises, and the logic of his complete
argument, a forthright answer that overturned a conceptual world—natural
selection works on organisms engaged in a struggle for personal success, as
assessed by the differential production of surviving offspring.
We all know that Darwin emphasized selection at the organismal level, but
many evolutionists do not appreciate the centrality of this claim within his theory;
nor do they recognize how actively he pursued its defense and illustra-
continent if all offspring survived and reproduced), then the principle of natural selection
follows by syllogistic logic. If only some offspring can survive (statement 1), then, on aver-
age (as a statistical phenomenon, not a guarantee for any particular organism), survivors will
be those individuals that, by their fortuity of varying in directions most suited for adaptation
to changing local environments, will leave more surviving offspring than other members of
the population (statement 2). Since these offspring will inherit those favorable traits
(statement 3), the average composition of the population will change in the direction of
phenotypes favored in the altered local environment.
As Darwin did himself in the Introduction to the Origin, nearly all textbooks and
college courses present the "bare bones" of natural selection in this fashion (I have done so in
more than 30 years of teaching). The device works well, but does not permit a teacher to go
beyond the simplest elucidation of selection as a genuine force that can produce adaptive
change in a population. In other words, the syllogistic core only guarantees that selection can
work. By itself, the core says nothing about the locus, the agency, the efficacy, or the range
of selection in a domain—the sciences of natural history—where all assessments of meaning
rest upon such claims about mode, strength, and relative frequency, once the prior judgment
of mere existence has been validated. Thus, an elucidation of this "syllogistic core" can only
rebut charges of hokum or incoherence at the foundation. An analysis of the three key issues
of the Darwinian essence, the subject of the rest of this chapter, then engages the guts of
natural history.