792 THE STRUCTURE OF EVOLUTIONARY THEORY
For proponents of punctuated equilibrium, speciation represents the primary
source for morphological changes that, by summation of increments, build trends
in the history of lineages. If a systematic bias in the nature of paleontological
evidence leads us to underestimate the number of speciation events, and if we can
still explain trends by this observed number (necessarily less than the actual
frequency), then the case for punctuated equilibrium becomes stronger by
affirmation in the face of a bias working against full expression of the theory's
effect. Thus, although we regret the existence of any bias that we cannot correct, a
systematic under representation of speciation events does not subvert punctuated
equilibrium because such a natural skewing of evidence makes the hypothesis even
more difficult to affirm—and support for punctuated equilibrium therefore emerges
in a context even more challenging than the unbiassed world of controlled
experimentation.
Moreover, one might even stress the bright side and recognize that such
biases may exist for interesting reasons in themselves—reasons that might even
enhance the importance of punctuated equilibrium and its implications. I doubt that
Levinton (1988, p. 379) intended the following passage in such a positive light, but
I would suggest such a reading: "One cannot rule out the possibility that speciation
is rampant, but morphological evolution only occurs occasionally when a
population is forced into a marginal environment and subjected to rapid directional
selection. What then becomes interesting is why the character complexes evolved
in the daughter species remain constant. This is, again, the issue of stasis, which I
believe to be the legitimate problem spawned by the punctuated equilibrium
model."
Finally, I am not sure that fossil species do strongly and generally underesti-
mate the frequency of true biospeciation—although I do accept that a bias, if
present at all, probably operates in this direction. The most rigorous empirical
studies on correspondence between well-defined paleospecies and true
biospecies—the works of Michaux and of Jackson and Cheetham discussed
above—affirm a one-to-one link between paleontological morphospecies and
extant, genetically defined biospecies.
Reasons for a potential systematic overestimation of biospecies
by paleospecies
If a bias did exist in this opposite direction, the consequences for punctuated
equilibrium would be troubling (as implied in the previous section on acceptable
and unacceptable forms of unavoidable natural biasing). For if we systematically
name too many species by paleontological criteria, then we might be affirming
punctuated equilibrium by skewing data in the direction of our favored theory,
rather than by genuine evidence from the fossil record. However, I doubt that such
a problem exists for punctuated equilibrium, especially since all experts—both
strong advocates and fierce critics alike (as the preceding discussion
documented)—seem to agree that if any systematic bias exists, the probable
direction lies in the acceptable opposite claim for underestimation of biospecies by
paleospecies.
I don't doubt, of course, that past taxonomic practice, often favoring the