854 THE STRUCTURE OF EVOLUTIONARY THEORY
Shapiro could not resolve the tempo or mode of the cladogenetic event itself, but
he showed that its direction cannot be extrapolated from an inferred pattern of
change by natural selection within the ancestral species.
Kelley (1983, 1984) then conducted a more extensive study of all molluscan
species with sufficiently rich vertical records in these classical and well-studied
Miocene beds of Maryland. She found trending within species for only 16 of 90
cases (17.8%) as defined by well-determined rank correlation coefficients between
a shell measurement and stratigraphic position. But for the majority of positive
coefficients, she found that the trend within a species is "oriented opposite to the
direction of the succeeding species's morphology, indicating a decoupling of
macroevolution from microevolution in those cases" (1983, p. 581).
PROPER AND ADEQUATE TESTS OF RELATIVE FREQUENCIES: THE
STRONG EMPIRICAL VALIDATION OF PUNCTUATED EQUILIBRIUMThe indispensability of data on relative frequencies
As stated before (p. 823), proponents of punctuated equilibrium have always
recognized that the theory cannot be proven, and can win only two minimal
validations—proof of plausibility and promise of testability—from
documentations, however rigorous and complete, of individual cases (as presented
in the last two sections). As its primary claim, therefore, punctuated equilibrium
must assert a dominant role for stasis within species and rapid cladogenesis
between species in the construction of macroevolutionary patterns at the
appropriate scale of speciation and trends across species within clades. This
assertion requires that punctuated equilibrium maintain a dominant relative
frequency in the origin of new paleospecies. Tests of the theory must therefore
focus upon percentages of occurrence in exhaustive, or at least statistically
definitive, surveys of particular taxa, faunas, and times.
Species cannot be conceptualized as indistinguishable beans in the
conventional bag of our standard metaphor for problems in probability—for the
nature of history grants uniqueness to times and taxa, and therefore precludes any
simple tabulation by global enumerative induction. We may, however, assess
relative frequencies for well-bounded situations restricted to taxa of a given fauna,
species within a monophyletic clade, or representatives of a particular time or
geological formation. Several such studies have been carried out, and effectively
all have found the clear signal of a dominant relative frequency for stasis and
punctuation, as predicted by the theory of punctuated equilibrium. I regard these
data as our most convincing indication of the validity and importance of
punctuated equilibrium as a primary generator of pattern in the history of life. I am
also surprised that this clear signal has not been more widely appreciated as the
most decisive result in a quarter century of research and debate about punctuated
equilibrium.
For reasons previously discussed under the heading of "publication bias" or
"Cordelia's dilemma" (see pp. 763-765), proper tests of relative frequencies cannot
be made by a "catch as catch can" style of simple enumeration