760 THE STRUCTURE OF EVOLUTIONARY THEORY
quantify—indeed, hardly anyone even bothered to mention or publish at all—the
most common pattern in the fossil record: the stasis of most morphospecies
throughout their geological duration.
All paleontologists recognized the phenomenon, but few scientists write
papers about failure to document a desired result. As a consequence, most
nonpaleontologists never learned about the predominance of stasis, and simply
assumed that gradualism must prevail, as illustrated by the exceedingly few cases
that became textbook "classics": the coiling of Gryphaea, the increasing body size
of horses, etc. (Interestingly, nearly all these "classics" have since been disproved,
thus providing another testimony for the temporary triumph of hope and
expectation over evidence—see Gould, 1972.) Thus, when punctuated equilibrium
finally granted theoretical space and importance to stasis, and this fundamental
phenomenon finally emerged from the closet, nonpaleontologists were often
astounded and incredulous. Mayr (1992, p. 32) wrote, for example: "Of all the
claims made in the punctuationalist theory of Eldredge and Gould, the one that
encountered the greatest opposition was the observation of 'pronounced stasis as
the usual fate of most species,' after having completed the phase of origination ... I
agree with Gould that the frequency of stasis in fossil species revealed by the
recent analysis was unexpected by most evolutionary biologists."
(To cite a personal incident that engraved this paradox upon my
consciousness early in my career, John Imbrie served as one of my Ph.D. advisors
at Columbia University. This distinguished paleoclimatologist began his career as
an evolutionary paleontologist. He accepted the canonical equation of evolution
with gradualism, but conjectured that our documentary failures had arisen from the
subtlety of gradual change, and the consequent need for statistical analysis in a
field still dominated by an "old-fashioned" style of verbal description. He schooled
himself in quantitative methods and applied this apparatus, then so exciting and
novel, to the classic sequence of Devonian brachiopods from the Michigan
Basin—where rates of sedimentation had been sufficiently slow and continuous to
record any hypothetical gradualism. He studied more than 30 species in this novel
and rigorous way—and found that all but one had remained stable throughout the
interval, while the single exception exhibited an ambiguous pattern. But Imbrie did
not publish a triumphant paper documenting the important phenomenon of stasis.
Instead, he just becomes disappointed at such "negative" results after so much
effort. He buried his data in a technical taxonomic monograph that no working
biologist would ever encounter (and that made no evolutionary claims at all)— and
eventually left the profession for something more "productive.")
Paradoxes of this sort can only be resolved by input from outside—for
gradualism, having defined contrary data either as marks of imperfection or
documents of disappointment, could not be refuted from within. Reassessment
required a different theory that respected stasis as a potentially fascinating
phenomenon worthy of rigorous documentation, not merely as a failure to find
"evolution." Eldredge and I proposed punctuated equilibrium in this explicit
context—as a framework and different theory that, if true, could validate