898 THE STRUCTURE OF EVOLUTIONARY THEORY
an icon for an argument, not a quantification. The full vernacular understanding of
complexity cannot be represented as a linear scale, although meaningful and
operational surrogates for certain isolated aspects of the vernacular concept have
been successfully designated for particular cases—see McShea, 1994.
I do not see how anyone could mistake the extreme value of a small tail in an
increasingly skewed distribution through time for the evident essence, or even the
most important feature, of the entire system. The error of construing this
conventional trend of extremes as the essential feature of life's history becomes
more apparent when we switch to the more adequate iconography of entire ranges
of diversity through time. Consider just three implications of the full view, but
rendered invisible when the sequential featuring of extremes falsely fronts for the
history of the whole.
- The salience of the bacterial mode. Although any designation of most
salient features must reflect the interests of the observer, I challenge anyone with
professional training in evolutionary theory to defend the extending tip of the right
tail as more definitive or more portentous than the persistence in place, and
constant growth in height, of the bacterial mode. The recorded history of life began
with bacteria 3.5 billion years ago, continued as a tale of prokaryotic unicells alone
for probably more than a billion years, and has never experienced a shift in the
modal position of complexity. We do not live in what older books called "the age
of man" (1 species), or "the age of mammals" (4000 species among more than a
million for the animal kingdom alone), or even in "the age of arthropods" (a proper
designation if we restrict our focus to the Metazoa, but surely not appropriate if we
include all life on earth). We live, if we must designate an exemplar at all, in a
persisting "age of bacteria"—the organisms that were in the beginning, are now,
and probably ever shall be (until the sun runs out of fuel) the dominant creatures on
earth by any standard evolutionary criterion of biochemical diversity, range of
habitats, resistance to extinction, and perhaps, if the "deep hot biosphere" (Gold,
- of bacteria within subsurface rocks matches the upper estimates for spread
and abundance, even in biomass (see Gould, 1996a, for a full development of this
argument). I will only remind colleagues of Woese's "three domain" model for
life's full genealogy (see Fig. 9-30), a previously surprising but now fully accepted,
and genetically documented, scheme displaying the phylogenetic triviality of all
multicellular existence (a different issue, I fully admit, from ecological
importance). Life's tree is, effectively, a bacterial bush. Two of the three domains
belong to prokaryotes alone, while the three kingdoms of multicellular eukaryotes
(plants, animals, and fungi) appear as three twigs at the terminus of the third
domain.
- The cause of the bacterial mode. "Bacteria," as a general term for the grade
of prokaryotic unicells lacking a complex internal architecture of organelles,
represent an almost ineluctable starting point for a recognizable fossil record of
preservable anatomy. As a consequence of the basic physics of self-organizing
systems and the chemistry of living matter—and under any