Punctuated Equilibrium and the Validation of Macroevolutionary Theory 799
simple, yet profound, argument has not infused the consciousness of evolutionists
because the implied and required hierarchical style of thinking remains so
unfamiliar and elusive to most of us. (In fact, and with some shame, I am
chagrined that I never recognized this evident and elegant resolution myself. After
all, I am supposedly steeped in this alternative hierarchical mode of thinking—and
I certainly have a strong stake in the problems of punctuated equilibrium.)
In short, Futuyma argues that we have been running on the wrong track, and
thinking at the wrong level, in trying to locate the reason for a correlation between
paleontological punctuations and events of speciation in a direct mechanism of
accelerated change promoted by the process of speciation itself. Yet Futuyma does
agree that a strong correlation exists (and has been demonstrated, in large part by
research and literature generated by debate about punctuated equilibrium). Since
we all understand (but do not always put into practice!) the important logical
principle that correlation does not imply causality (the post hoc fallacy), an
acknowledgement of the genuine link doesn't commit us to any particular causal
scheme—especially, in this case, to the apparently false claim that mechanisms of
speciation inherently enhance evolutionary rates.
Futuyma begins by arguing that morphological change may accumulate
anywhere along the temporal trajectory of a species, and not exclusively (or even
preferentially) during the geological moment of its origin. What then could
produce such a strong correlation between events of branching speciation and
morphological change from an ancestral phenotype to the subsequent stasis of an
altered descendant? Futuyma—and I am somewhat rephrasing and extending his
argument here—draws an insightful and original analogy between macroevolution
and the conventional Darwinism of natural selection in populations.
The operation of natural selection requires that Darwinian individuals interact
with environments in such a manner that distinct features of these individuals bias
their reproductive success relative to others in the population. As a defining
criterion of Darwinian individuality, entities that interact with the environment
must show "sufficient stability" (see discussion on pp. 611-613)—defined in terms
of the theory and mechanism under discussion as enough coherence to perform as
an interactor in the process of natural selection.
Darwin recognized that organisms operate as fundamental interactors for
as pursued by neontologists interested in evolutionary mechanisms with the "historical"
themes favored by systematists and paleontologists—all (to borrow a line from
elsewhere) "in order to form a more perfect union."
We need to identify and to define rigorously questions to which both
synchronic and historical evolution can make truly indispensable
contributions. Some such questions have already been posed, so we now find
systematists and population geneticists converging on the analysis of
macromolecular sequences, geneticists publishing in Paleobiology (thanks to
the healthy stimulus of punctuated equilibrium), systematists and students of
adaptation finding a rapprochement in the use of phylogenetic information to
test hypotheses of behavioral, physiological, and other adaptations.