Tiers of Time and Trials of Extrapolationism 1321
me. And yet, I do not think that the actual history of life maps the expectations of his
argument, thus leaving us with a central evolutionary paradox. Nearly all-vernacular
understanding of evolution, and much professional interpretation as well, would deny
my last statement and affirm a broad signal of such progress. Although I do
appreciate the appeal of an argument based on "ratcheting" for an accretion of levels
in complexity through time—for certain kinds of more elaborate aggregation and
integration cannot viably disassemble once conjoined, although any level can be lost
by extinction (my interpretation of the claims presented by Maynard Smith and
Szathmary, 1995, for "the major transitions in evolution")—I fail to find any rationale
beyond anthropocentric hope and social tradition for viewing such a sequence as a
fundamental signal, or an expression of the main weights and tendencies in life's
history. After all, two of the three great boughs on life's phyletic tree remain
prokaryotic, while all three multicellular kingdoms extend as twigs from the terminus
of the third bough. If we regard intellectual skepticism against anthropocentrism as a
worthy cause, I don't see how we can deny that the persisting domination, and
continued rosy prospects, of prokaryotes epitomize the primary aspect of life's history
(see Gould, 1996a, and pp. 897-901 of this book for an elaboration of this argument).
And if we must honor animals in our parochialism, arthropods surely hold an
enormous edge over vertebrates.
I have referred (Gould, 1985a) to this failure of Darwin's sensible argument to
impress itself upon the actual history of life as "the paradox of the first tier"—thus
also giving away my preference between the two major possibilities for resolution
(see forthcoming discussion, and my defense of nonfractal "tiers" of time with
different predominating causes and patterns, with Darwin's good argument operating
only at the first tier, and unable to "push through" to impose a pervasive vector upon
the history of life). If we accept my characterization of this situation as a paradox,
then we must ask why a valid argument for progress, based upon the uniformitarian
extrapolation through geological time of the microevolutionary mechanics of natural
selection, fails to make its anticipated mark upon earthly phylogeny. As an abstract
issue in logic, two "pure" end-member solutions can be specified because the basic
proposition includes two assertions, with the falsification of either being sufficient to
destroy the full argument even if the other assertion remains entirely valid. (Needless
to say, the actual resolution of the paradox in our messy "real world" will, no doubt,
combine aspects of both with numerous other factors as well.)
The first assertion holds that natural selection, operating primarily by biotic
competition under ecological plenitude, will indeed generate a bias towards
"progress" by granting a statistical edge to general mental and biomechanical
improvement. The second assertion then holds that this micro-evolutionary edge
should accumulate smoothly, through time and up levels, to yield the general vector
of life's progress that Darwin described in his geological chapters (see quotes on pp.
467 —479). Thus, refutation at the first end-member accepts full fractality and
extrapolation from microevolutionary