Species as Individuals in the Hierarchical Theory of Selection 681
"the measure of all things"—ambiguous, that is, in embodying both positive and
negative meanings: positive for humanistic reasons of ubiquitous self-valuing that
might lead to some form of universal brotherhood and compassion; but negative
because our own "measure" can be so parochially limiting, and therefore so
conducive to misunderstanding other scales if we must assess these various
domains by the allometric properties of our limited estate.
This issue becomes especially serious for the hierarchical theory of selection.
Humans hold status as both evolutionary individuals and organisms— yet all other
"separate but equal" evolutionary individuals at other hierarchical levels are not
organisms. Unfortunately, organisms constitute a very special and distinctly odd
kind of evolutionary individual, imbued with unique properties absent from (or
much weaker in) other individuals (at other levels) that are equally potent as
evolutionary agents. But if we mistakenly regard our own unique properties as
indispensable traits for any kind of evolutionary individual—the classic error of
parochialism—then we will devalue, or even fail to identify, other individuals
defined by different properties and resident at other levels.
I shall explore some of these crucial differences in the next two sections
(disparate properties of the six major levels; and extensive comparison of
organisms and species as evolutionary individuals). In this introductory comment, I
only wish to emphasize that the uniqueness of the organism as a unit of selection
lies in securing individuality by maximal homeostatic interaction among parts, an
integration that ties each subpart to the fate of all, and therefore strongly
discourages any "breakout" or differential proliferation (by suborganismic
selection) from within. To be sure, such integration represents a powerful strategy
for individuation, but this strategy does not specify the only legitimate path, and
other potent evolutionary individuals use other mechanisms. For this reason, I
regret that Wilson and Sober (1994) so emphasize these "organic" properties of
individuality in their general definition, meant to apply to all levels. This parochial
focus leads them to downplay the individuality of units of selection at other levels,
where different definitional criteria predominate—in species, for example, where
the maintenance of boundaries by reproductive isolating mechanisms, and the
mixture of sub-parts in replenishment (sexual reproduction), maintain cohesion and
stability just as well as organisms do by the different strategies of homeostasis and
functional interaction of subparts.
Redressing the tyranny of the organism: comments on
characteristic features and differences among six
primary levels
I have little tolerance for numerical mysticism. I feel no special affinity for threes
(as trinities), fours (Jung's primal archetype), fives (for fingers or echinoderms),
sevens (for notes of the musical scale, planets in the Ptolemaic system, and so
much else), or nines (the trinity of trinities). Similarly, in recognizing six
hierarchical levels for this discussion—genes, cells, organisms, demes, species,
and clades—I only utilize a device of convenience, and do not make