706 THE STRUCTURE OF EVOLUTIONARY THEORY
But this focus on the biotic mode has always been indefensible as a claim for
exclusivity, or even dominant relative frequency. In Darwin's own time, Huxley
ridiculed this notion as "the gladiatorial theory of existence," while Kropotkin
(1902) and others constructed alternatives based on cooperation in sympatry and
the prevalence of abiotic competition in most environments (see Todes, 1988;
Gould, 1991b). Darwin himself clearly favored an expansive concept of interaction
with environments in natural selection—as when he insisted, in a famous passage
(1859, p. 62), that "a plant on the edge of a desert" struggles for existence against
the drought and other features of the physical environment just as surely as "two
canine animals in a time of dearth" struggle more overtly for a limited supply of
meat.
This point becomes important when we try to translate this debate about
organisms to a definition of higher-level interactors. Biotic competition does
require sympatry for direct and literal struggle, while abiotic competition imposes
no such conditions, and must often occur among organisms that never encounter
each other, even while living in sympatry. If we use biotic competition as our
(often unconscious) paradigm for the entire, and far broader, concept of
interaction, then we too easily become unduly committed to the false restriction
that interactors must be able to duke it out directly. In upward translation, this bias
leads to the idea that species-individuals can't be interactors unless they live in the
same place, and thus maintain a potential for engaging in some analog of overt
battle.
But interaction at the canonical level of organisms doesn't demand direct
contact, or even life in the same place—and no one has denied that organisms
operate as quintessential interactors, and units of selection. If abiotic competition
dominates the history of life—as many distinguished researchers insist (see
references in Allmon and Ross, 1990), at least for many groups in many
circumstances—then potential for direct contact cannot be invoked as a primary
criterion for defining interactors.
Williams (1992) has strongly asserted the non-necessity of sympatry (and
resulting potential for direct "struggle") in defining higher-level interactors— and
he uses the same analogy here advanced for asserting a similar non-necessity at the
organismal level. I presented the full quote before, but repeat the operative line
here (1992, p. 25): "One issue is whether the populations that bear the gene pools
need be in ecological competition with each other. I believe that this is not
required, any more than individuals within a population need interact ecologically
to be subject to individual selection." Later, Williams specifically criticizes
Damuth's definition of avatars on this basis. Speaking of populations not in direct
competition, but subject to similar stresses (a common predator in their separate
environments in this hypothetical case), Williams writes (1992, p. 52): "I am
inclined to recognize that clade selection is operating even here, unlike Damuth,
who maintains that only sympatric avatars, populations in ecological competition,
can be alternatives subject to selection. Allopatric forms may not be ecological
competitors, for the inattention of a predator or anything else, but they compete for
representation in the biota, the ultimate prize in clade selection."