790 THE STRUCTURE OF EVOLUTIONARY THEORY
Hoffman (1989, p. 115) invokes this argument to assert the untestability,
hence the nonscientific status, of punctuated equilibrium:
Long-term evolutionary stasis of species, however, simply cannot be tested
in the fossil record. Paleontological data consist solely of a small sample of
phenotypic traits—little more than morphology of the skeletal parts—which
does not allow us to make any inference about changes in a species's
genetic pool or even about changes of the frequency distribution of
phenotypes in a phyletic lineage. The no preserved portion of the phenotype
of each fossil species is so extensive that it may always undergo
considerable evolutionary changes that remain undetectable by the
paleontologist. What appears then to the paleontologist as a species in
complete evolutionary stasis may in fact represent a succession of fossil
species or perhaps a whole cluster of species, a phylogenetic tree with a
sizable number of branching points, or speciation events.While I freely admit all these arguments for under representation of true
species in fossil data, I do not comprehend how punctuated equilibrium could be
thus rendered untestable, or even seriously compromised (see further arguments in
Gould, 1982c and 1989e; and Gould and Eldredge, 1993). I base my argument on
two logical and methodological principles, not on the probable empirical record
(where I largely agree with our critics).
THE PROPER STUDY OF MACROEVOLUTION. By consensus, and accepting a
criterion of testability, science does not include, within its compass of inquiry,
fascinating questions that cannot be answered (even if they address potentially
empirical subjects). For example, and for the moment at least, we know no way to
ask a scientific question about what happened before the big bang, for compression
of universal matter to a single point of origin wipes out all traces of any previous
history. (Perhaps we will eventually devise a way to obtain such data, or perhaps
the big bang theory will be discarded. The question might then become
scientifically tractable.) Similarly, we know that many kinds of evolutionary events
leave no empirical record— and that we therefore cannot formulate scientific
questions about them. (For example, I doubt that we will be able to resolve the
origins of human language, unless written expression occurred far earlier than
current belief and evidence now indicates.)
The nature of the fossil record leads us to define macroevolution as the study
of phenotypic change (and any inferable correlates or sequelae) in lineages and
clades throughout geological time. Punctuated equilibrium proposes that such
changes generally occur in discrete units or quanta in geological time, and that
these quanta represent events of branching speciation. Thus, we do identify
speciation as the source of raw material for macroevolutionary change in lineages.
But we do not, and cannot, argue (or attempt to adjudicate at all) the quite different
proposition that all speciation events produce measurable quanta of
macroevolutionary change. The statement—our proposition—that nearly all
macroevolutionary change occurs in increments of speciation carries no
implications for the unrelated claim, often imputed to