720 THE STRUCTURE OF EVOLUTIONARY THEORY
673). But this basic ratcheting already reveals some pivotal differences between
the evolution of organism-individuals and species-individuals. In Table 8-1, line
I2a, for example, notes the profoundly different outcome that usually ensues when
particular parts of the individual proliferate differentially and crowd out other
parts. Such a process usually spells disaster for a complex multicellular
organism—and we call the result cancer—because parts lack independent viability
(and therefore harm both themselves and their collectivity, the organism, by
unchecked proliferation), and because organisms build coherence (an important
criterion of individuality) by functional integration and division of labor among
parts. But species achieve equal coherence by other routes. The parts of a
species—that is, its component organisms—do have independent viability;
moreover, their interests in proliferation often coincide with the health of the
enclosing species. Thus, in a species-individual, differential proliferation of some
parts at the expense of other parts does not lead to death of the full entity, but
usually to adaptation by anagenesis.
Criteria for individuality
Moving to the second category of criteria for individuality (see pp. 602-613 of this
chapter), we may regard the species-level analogs of organismal birth and death
(lines III—2)—speciation and extinction—as both evident and well recognized.
But the different causes of cohesion (line 113) are both fascinating and portentous
throughout the chart. I only remind readers that the mechanisms used by species,
while not clamping down so hard on lower levels, and therefore providing
substantial "play" for interaction between organismal and species selection,
provide species with as much coherence and stability as the "standard" devices of
morphological boundaries, internal policing and functional integration among
parts, do for organisms.
Important differences arise in the mode of production for novel variation in
newborn individuals. Mutation supplies this attribute at the organismal level.
(Following conventional usage, I consider recombination in sexual organisms as a
device for spreading variation among individuals, although I recognize, of course,
that novel combinations also arise thereby. In asexual organisms, a better analog
for species in any case, mutation alone supplies new variation.) Speciation itself is
not the proper analog of mutation at the species level (an error previously made
both by me, in Gould and Eldredge, 1977, and by Stanley, 1975). Speciation, the
production of a new species-individual by budding, is the analog of organismal
birth, particularly the birth of asexual organisms. We made this error by
inadequately interpreting one of the most interesting differences between
organisms and species as evolutionary individuals. The birth of a new organism,
particularly in asexuals, may or may not engender any substantial difference from
parental form or genetics. But the birth of a new species necessarily includes the
generation of enough difference from ancestors to preclude reproductive
amalgation between the parts (organisms) of the two species. We therefore mistook
a forced correlate of birth at the species level (change at speciation) with the
process of