Species as Individuals in the Hierarchical Theory of Selection 705
debate. Most discussants, including Brandon, Gould, Jablonski, Lloyd, Stanley,
and Vrba, strongly support the concept of species as units of selection; while
Damuth and Eldredge grant species a role as replicators, but not as interactors, and
therefore not as agents of selection. Grantham (1995) has tried to mediate these
positions with a compromise that will, I suspect, satisfy neither side.
Critics allow that species may be "fundamental units" of macroevolution in
some sense—but they say, only as the replicators that serve as "atoms" of cladistic
phylogeny, and not as interacting units that forge macroevolutionary change by
active competition in natural environments. (Eldredge, for example, includes
species in the genealogical column of his two-hierarchy scheme —see page 642 for
a critique—but not in his economic column of interactors.) A species, the critics
continue, may live in too broad a range of environments, and over too wide a
geographic range—often discontinuous to boot—to serve as an interactor, or unit
of selection. Moreover, although individual populations of two species may
compete sympatrically over a well-delineated geographic range, entire species
rarely maintain sufficient overlap to interact with each other as complete units.
To resolve this apparent dilemma, Damuth (1985) proposes that we define a
new interactor corresponding most closely to the hierarchical level where species
serve as replicators. Using a criterion of direct competition in sympatry, Damuth
proposes the term "avatar" for such interactors, defined as sympatric populations in
ecological competition, and therefore interpretable as alternatives subject to
selection. Grantham's (1995) "compromise" position maintains allegiance to
Damuth's insistence upon potential interaction in sympatry. Grantham defends
species selection, and regards species as potential interactors—but he would
restrict any particular study of species selection to members of clades living in the
same broad region. He writes (1995, p. 311): "I suggest that paleontologists focus
on geographically constrained portions of monophyletic clades."
I would raise three arguments against this proliferation of terms and
categories—and for the status of species as adequate interactors.
- A standard mode of construing competition among organisms has beguiled
us into thinking that interaction requires sympatry. As argued in Chapter 6 (pp.
470 - 477), Darwin strongly asserted the predominance of biotic over abiotic
competition as the only promising path for a defense of progress in evolution. This
preference has passed through the Victorian fascination with overt battle as a
defining mode of competition, right into our present times, with continuing
Tennysonian metaphors about "nature red in tooth and claw" (see Gould, 1992a),
and newspaper stories about firms engaged in Darwinian struggles to the death as
they vie directly for the allegiance of a limited population of consumers. (As I
revised this chapter in the summer of 2000, a new magazine for "business evolving
in the information age" made its debut under the name Darwin—also available on
line at http://www.darwin-mag.com.))