810 THE STRUCTURE OF EVOLUTIONARY THEORY
argument for considering the validity of punctuational change at all levels.
Just as the careful watchdog at any scientific meeting will unhesitatingly call
out "what's the scale" when a colleague fails to include a measurement bar on a
slide of any important object, we must always ask, "what's the level" when we
analyze the causal basis of any evolutionary pattern. Punctuational clone selection
can yield gradualism within collectivities conventionally (if dubiously) called
"species," just as punctuated equilibrium, acting on species as Darwinian
individuals, can produce gradual trends in the overall history of lineages and
clades.
GENOTYPES. Punctuated equilibrium is a theory about the evolution of
phenotypes (both in concept and in operational testability for paleontological
hypotheses), and correlations with genotypic patterns provide neither a crucial test
nor even any necessary prediction. For example, critics of punctuated equilibrium
have often argued that the apparently cumulative character of overall genetic
distances among members of an evolving clade, expressed as a high correlation
between measured disparities and independently derived times since divergence
from a common ancestor—the kind of information that, in idealized (but rarely
encountered) situations, yields a rough "molecular clock"—should argue strongly
against punctuational styles of evolution, while affirming anagenetic gradualism.
But, leaving aside the highly questionable empirical status of these claims, the
hypothesis of punctuated equilibrium would not be affected by positive outcomes,
even at much higher relative frequency than the known history of life apparently
validates. In supposing that "molecular clocks" tick against the requirements of
punctuated equilibrium, we fall into two bad habits of thinking that impede
macroevolutionary theory in general, and therefore rank as important conceptual
barriers against the theses of this book. First, reductionistic biases often lead us to
seek an "underlying" genetic basis for any overt phenomenon at any scale, and then
to view data at this level as a fundamental locus for proper evolutionary
explanation. (But consider only two among many rebuttals of such a position: (1) a
genetic pattern may be