Punctuated Equilibrium and the Validation of Macroevolutionary Theory 997
or shortest shrift awarded to the topic in standard textbooks of the 1950's and 1960's
(as documented in Chapter 7, pages 579-584).
At the level of details and content, many textbooks provide gratifyingly accurate
(if often critical) definitions and appraisals of punctuated equilibrium.
Unsurprisingly, textbooks written by paleontologists have generally provided the
clearest treatments. Nield and Tucker (1985, p. 162), for example, stress the role of
punctuated equilibrium in rendering the fossil record operational for evolutionary
studies: "We usually witness sudden appearance of new species, followed by long
static periods and ultimate extinction. Formerly it was supposed that this fact
reflected the incompleteness of the fossil record, but the belief now is that it
represents something very important about the evolutionary process." Similarly, Dott
and Prothero (1994, p. 61) end their section on "The fossil record and evolution" by
stating:
To some paleontologists, species are more than just populations and genes.
They are real entities that seem to have some kind of internal stabilizing
mechanism preventing much phenotypic change, even when selection forces
change. Clearly, the fossil record produces some unexpected results that are
not yet consistent with everything we know about living animals and
laboratory experiments. This is good news. If the fossil record taught us
nothing that we didn't know already by biology, there wouldn't be much point
to evolutionary paleontology.Finally, Dodson and Dodson (1990, p. 520) provide an excellent summary on the
implications of punctuated equilibrium for evolutionary theory:
Most evolutionary biologists are prepared to acknowledge that punctuated
equilibrium is an important phenomenon, even if somewhat less so than it’s
more enthusiastic advocates claim. And population geneticists, who have
labored mainly to clarify the genetic basis of evolutionary change, may now
have to give greater attention to the problem of evolutionary stasis ... Thus,
the question is not whether punctuated equilibria occur, but how general they
are and whether they can be absorbed into the modern evolutionary synthesis.Among the best treatments of punctuated equilibrium in textbooks, I would cite
Kraus's book for high school biology (1983), the continuing efforts of Alters and
McComas (1994) to design a high school curriculum based on punctuated
equilibrium, and the college textbooks by Avers (1989) and Price (1996). Much of
the graphical material has also been highly useful—as in Price's ingenious inclusion
of both spatial and temporal dimensions to show how allopatric speciation yields both
stasis and punctuation in the fossil record—see Figure 9-39.
As a model of excellence, and of clear, accurate, stylish writing as well, the
treatment of punctuated equilibrium in the most popular textbook of the 1980's
embodies the reasons for this volume's well-deserved status. Helena Curtis was a
thoughtful writer, not a professional biologist, but she mastered the material and
could write circles around her competition. (I also know,