668 THE STRUCTURE OF EVOLUTIONARY THEORY
and therefore sacrifices all utility as an empirical proposition in science.
Fortunately, we can unite both criteria of emergent fitnesses and characters into a
unified scheme that establishes two realms of species selection, one more inclusive
than the other, but that also identifies a domain of species sorting leading us to
reject causation by species selection.
Grantham (1995) has presented such a scheme, reproduced here as Figure 8 - 4.
(I had independently developed the same system, almost with the same picture, in
preparing to write this chapter. I mention this not to compromise Grantham's
originality or priority in any way—for priority is chronology, and his cannot be
gainsaid! — but to express the firm and almost eerie satisfaction that such a
"multiple" formulation brings (see Merton, 1965), and to offer this example as
proof that the inherent logic of a complex argument often drives independent
researchers to a definite and almost ineluctable result-validating in this case the
coherence of this "take" on species selection.)
Grantham's diagram circumscribes two realms of species selection, labeled as
"hierarchical explanations." The A realm contains Vrba's firmest examples based
on emergent characters, while the B realm adds Lloyd's cases based on the
emergent fitnesses associated with aggregate species-level characters. (Vrba, of
course, would restrict species selection to the A realm, and ascribe the B realm to
the "effect hypothesis"—but everyone seems to agree on the structure and
relationships of the realms.) The A realm seems firmer because emergent
characters count as adaptations of species, and maintain no expression
8 - 4. Grantham's 1995 epitome of criteria for invoking species selection in hierarchical models.
The A domain includes rare best cases of species selection based on emergent species-level
traits. The B domain adds aggregate traits that affect irreducible species-level fitness, and
therefore also participate in species selection under the interactor approach. The aggregate and
reducible traits of the C domain belong only to organisms and cannot figure in arguments for
species selection.