1292 THE STRUCTURE OF EVOLUTIONARY THEORY
(see Gould and Lloyd, 1999 for this extension of allometry) possessed by virtue of
their sizes and cyclings, but absent in organisms for equally inherent reasons of their
own constitution. As argued at length in Chapter 8, organisms maintain their
biological individuality as discrete entities by strategies of intricate and precise
functional interrelationships among constituent parts, and by maintenance of internal
and external boundaries (immune systems and skins) to exclude the subparts of other
individuals from their geographic space. Thus, and most characteristically, if not
uniquely, the organism maintains its integrity by rigorous policing, and by active
suppression of differential proliferation among its subparts, a result that could
otherwise follow from positive selection upon the individuals of lower levels within
the organism itself (especially upon cell lineages, with the failure of such organismal
policing leading to the result that we call cancer).
Thus, organisms sacrifice the benefits of including more upwardly cascading
effects as components of their exaptive pool because they work so hard to preserve
their distinctive style of individuality by suppressing the churning of lower levels of
selection within their bodies. But, by important contrast, species construct their
equally powerful integrity and discreteness by different means that do not require
such suppression of upwardly cascading effects. Species maintain their boundaries
primarily by reproductive isolation of their subparts (the organisms that constitute
their populations) from subparts of other species-individuals. By permitting their
subparts to reproduce only with each other, and not with subparts of other species-
individuals, a species maintains its integrity, and constructs its boundary, with just as
much clarity and efficiency as organisms can muster by different strategies of
functional integration among organs and active exclusion of invaders. This different,
but equally efficient, modality of species does not include the suppression of lower
level selection as a consequence. Therefore, species remain open, as organisms do
not, to experiencing a full and rich range of cross-level spandrels, injected as
consequences of selection acting on lower-level individuals (primarily upon
organisms) within their boundaries.
Now—and here's the rub—we have generally viewed this openness of species as
a negative sign of impotence at this higher level of biological organization. For,
reasoning from our parochial perspective as organisms—and falsely supposing that
organismal ways must be universally best ways—we have viewed the species's
nonsuppression of upwardly cascading spandrels as a mark of its failings as a
potential unit of selection. But perhaps we should reverse this perspective and learn
to respect the distinct allometric properties of species individuality as potential
strengths for a different mode of selection— with the higher frequency of cross-level
spandrels viewed as a source of rich potential denied to organisms, rather than as a
mark of inefficiency imposed upon species.
The species-individual, as a Darwinian interactor in selection at its own level,
operates largely with cross-level exaptations arising from unsuppressed evolution of
subparts (primarily organisms) at lower levels within itself. Such