Punctuated Equilibrium and the Validation of Macroevolutionary Theory 823
basis of punctuated equilibrium. This literature includes: the 1982 symposium in
Dijon, France, entitled Modalites, rythmes, mechanismes de devolution biologique:
gradualisme phyletique ou equilibres ponctues and published as Chaline, 1983; the
1983 Swansea symposium of the Paleontological Association (United Kingdom)
on "Evolutionary case histories from the fossil record" and published as Cope and
Skelton (1985); the book The Dynamics of Evolution: The Punctuated Equilibrium
Debate in the Natural and Social Sciences (Somit and Peterson, 1992) that began
as a symposium for the annual meeting of the American Association for the
Advancement of Science, and then appeared as a special issue (1989) of the
Journal of Biological and Social Structures; the 1992 symposium of the
Geological Society of America on "Speciation in the Fossil Record," held to
celebrate the 20th anniversary of punctuated equilibrium, and published in book
form as Erwin and Anstey (1995); and the 1994 Geological Society of America
symposium on coordinated stasis, published in a special issue of the journal
Palaeogeography, Palaeoclimatology, Palaeoecology in 1996 (volume 120, with
Ivany and Schopf as editors). Several other unpublished symposia, including the
notorious Chicago macroevolution meeting of 1980 (see pages 981-984), focused
upon the topic of punctuated equilibrium. Finally, several books have treated
punctuated equilibrium as an exclusive or major topic, including the favorable
accounts of Stanley (1979), Eldredge (1985, 1995), and Vrba (1985a), and the
strongly negative reactions of Dawkins (1986), Dennett (1995), Hoffman (1989),
and Levinton (1988).
As emphasized throughout this book, most general hypotheses in natural
history, with punctuated equilibrium as a typical example, cannot be tested with
any single "crucial experiment" (that is, by saying "yea" or "nay" to a generality
after resolving a case with impeccable documentation), but must stand or fall by an
assessment of relative frequency. Moreover, we can't establish a decisive relative
frequency by simple enumerative induction (as in classical "beans in a bag" tests of
probability)—for individual species cannot be treated as random samples drawn
from a totality with a normal (or any other kind of simple) distribution, but
represent unique items built by long, complex and contingent histories. Time,
taxon, environment and many other factors strongly "matter," and no global
evaluation can be made by counting all cases equally. We may, however, be able to
reach robust solutions for full populations within each factor—for planktonic
forams, terrestrial mammals, Devonian brachiopods, or species of the Cambrian
explosion, for example. Part C of this section reports several such studies, nearly
all finding a predominant relative frequency for punctuated equilibrium.
Nonetheless, hundreds of individual cases have been documented since we
proposed punctuated equilibrium in 1972. I do not think that most authors pursue
such work under any illusion that they might thus resolve the general debate, but
rather for the usual, and excellent reasons of ordinary scientific practice.
Researchers pursue such studies in order to apply promising general concepts to
cases of special interest that draw upon their unique skills and expertise.