Punctuated Equilibrium and the Validation of Macroevolutionary Theory 937
great discomfort with the aimless cyclicity of Ecclesiastes, however much we may
admire the literary power: "The thing that hath been, it is that which shall be; and
that which is done is that which shall be done; and there is no new thing under the
sun" (Ecclesiastes 1:9).
But the undeniable salience of trends—a psychological comment about our
focus of attention—bears no necessary relationship to the relative frequency or
causal weight of this phenomenon in the natural history of clades. How many
monophyletic clades feature sustained and substantial trends in major characters of
functional importance—and what percentage of characters participates in trends
that do exist in such clades? Indeed, we have no idea whatever, for no neutral
compilations exist. No one has ever tabulated the number or percentage of non-
trending clades within larger monophyletic groups. The concept of a non-trending
clade—the higher-level analog of a species in stasis—has never been explicitly
formulated at all. If only one percent of clades exhibited sustained trends, we
would still focus our attention upon this tiny minority in telling our favored version
of the story of life's history.
(Ironically, stable lineages become salient enough to catch our attention only
at the extreme that we call "living fossils"—species or lineages supposedly
unchanged during such long stretches of geological time that their stability
becomes a paradox in a world of Darwinian evolutionary flux and continuity. As a
double irony—see pages 817-820 for a full discussion in the light of punctuated
equilibrium's different reading—we have also thoroughly misinterpreted this
phenomenon under the same gradualistic bias that inspired our notice in the first
place! The classical "living fossils" (the inarticulate brachiopod Lingula, the
horseshoe crab Limulus polyphemus, the extant coelacanth) are not long-lived as
species (Limulus polyphemus, for example, has no fossil record at all), but rather
belong to clades with such a low speciation rate that little raw material for cladal
trending has been generated over the ages.)
I suspect that most clades, while waxing and waning in species diversity
through time, show no outstanding overall directionality. But we do not know
because the literature has never recognized, or attempted to tabulate, the frequency
of such "Ecclesiastical" clades that change all the time, but "go" nowhere in
particular during their evolutionary peregrinations. Paleontologists achieved no
sense of the strength of punctuated equilibrium, even though Eldredge and I had
formulated the theoretical apparatus, until researchers studied the relative
frequencies of stasis and punctuation in entire faunas, or entire clades, by full
sampling and with no predisposing bias to favor one kind of result—see discussion
on pages 854-874 for this extensive and growing literature. Similarly, we will not
know the general fate of clades until we ratchet this methodology one notch higher,
and sample sets of clades not identified by our prior sense of their evolutionary
"interest." Stasis is data at the species level. Non-trending is data at the clade level.
Budd and Coates (1992) broke conceptual ground in devoting an entire paper
to such Ecclesiastical non-directionality in the actively evolving and speciating
clade of montastraeid corals during 80 million years of Cretaceous