582 THE STRUCTURE OF EVOLUTIONARY THEORY
argument takes two forms. Some authors explicitly exclude paleontology from the
theoretical game:
Evolution can be studied on the population level only with living
organisms. The fossil record provides too few data to allow such treatment;
it merely allows paleontologists to reconstruct the history of animal and
plant groups. The population approach makes it possible to ask such
questions as: what is the rate of evolution in a given species? What factors
influence the course or rate of evolution? What conditions are necessary for
evolution to begin or cease? (Baker and Allen, 1968, p. 524). [I do not see
why paleontologists cannot address all three of these questions with data
from the morphology of fossils and their temporal distribution.]But I must confess that a stronger and more focused form of this argument has
long evoked my deeper distress, and has served, in substantial measure, as the
impetus for personal career choices in research, and for my eventual decision to
write this book. I refer to the claim, repeated almost as a catechism, and obviously
copied from textbook to textbook, that macroevolution poses no problem not
resolvable by a further understanding of allelic substitutions directed by natural
selection in contemporary populations. We may move smoothly from one gene to
an entire Bauplan, and extrapolate upwards from a few generations to a geological
era. No additional problems arise in temporal vastness. Macroevolution becomes
little more than industrial melanism writ large. But can we even imagine, in a
world dominated by effects of scale, that such a maximal extension of form and
time will engage not a single force or principle beyond the factors fully in evidence
at the lowest level? Can the smallest scales really provide an entirely sufficient
model for the largest? Can a uniformitarianism this rigid truly be sustained? If so,
then paleontology only represents a playground for the full display of
microevolutionary muscle—and textbooks need not consider the fossil record as
more than an archive of the pathways carved by this power.
Most standard textbooks make this confident assertion based on little beyond
hope and tradition—thus making macroevolution a nonsubject. Bonner (1962, p.
48), for example, writes: "There is no reason to believe that these large changes are
not the result of the very same mechanics of the small changes of industrial
melanism. One involves a small step over a few years; the other involves many
thousands of steps over millions of years."
Curtis (1962, p. 712), in a best-selling text of the 60's, begins her short section
on macroevolution by stating: "Can the same processes that slowly shape the seed
of mustard weed or change the color of the peppered moth create the differences
between elephants and daisies or between butterflies and redwood trees? Darwin
believed so—all he felt that was needed was time, millions of years of slow
change. Today, almost all evolutionists are, in principle, in general agreement with
Darwin's conclusions."
Several texts even present this canonical argument as their only statement
about macroevolution. I end this chapter by quoting two striking examples of