its pre-Darwinian struggles with more inchoate formulations before 1859), these
three principles of central logic defined the themes of deepest and most persistent
debate—as, in a sense, they must because they constitute the most interesting
intellectual questions that any theory for causes of descent with modification must
address. The historical chapters of this book's first half then treat the history of
evolutionary theory as responses to the three central issues of Darwinian logic
(Chapters 3-7).
- As the strict Darwinism of the Modern Synthesis prevailed and "hardened,"
culminating in the overconfidences of the centennial celebrations of 1959, a new
wave of discoveries and theoretical reformulations began to challenge aspects of
the three central principles anew—thus leading to another fascinating round of
development in basic evolutionary theory, extending throughout the last three
decades of the 20th century and continuing today. But this second round has been
pursued in an entirely different and more fruitful manner than the 19th century
debates. The earlier questioning of Darwin's three central principles tried to
disprove natural selection by offering alternative theories based on confutations of
the three items of central logic. The modern versions accept the validity of the
central logic as a foundation, and introduce their critiques as helpful auxiliaries or
additions that enrich, or substantially alter, the original Darwinian formulation, but
that leave the kernel of natural selection intact. Thus, the modern reformulations
are helpful rather than destructive. For this reason, I regard our modern
understanding of evolutionary theory as closer to Falconer's metaphor, than to
Darwin's, for the Duomo of Milan—a structure with a firm foundation and a
fascinatingly different superstructure. (Chapters 8-12, the second half of this book
on modern developments in evolutionary theory, treat this third theme.)
Thus, one might say, this book cycles through the three central themes of
Darwinian logic at three scales—by brief mention of a framework in this chapter,
by full exegesis of Darwin's presentation in Chapter 2, and by lengthy analysis of
the major differences and effects in historical (Part 1) and modern critiques (Part 2)
of these three themes in the rest of the volume.
The basic formulation, or bare-bones mechanics, of natural selection is a
disarmingly simple argument, based on three undeniable facts (overproduction of
offspring, variation, and heritability)' and one syllogistic inference (natural
selection, or the claim that organisms enjoying differential reproductive success
will, on average, be those variants that are fortuitously better adapted to changing
local environments, and that these variants will then pass their favored traits to
offspring by inheritance). As Huxley famously, and ruefully, remarked (in self-
reproach for failing to devise the theory himself), this argument must be deemed
elementary (and had often been formu-
Two of these three ranked as "folk wisdom" in Darwin's day and needed no further
justification—variation and inheritance (the mechanism of inheritance remained
unknown, but its factuality could scarcely be doubted). Only the principle that all
organisms produce more offspring than can possibly survive—superfecundity, in
Darwin's lovely term—ran counter to popular assumptions about nature's benevolence,
and required Darwin's specific defense in the Origin.
14 THE STRUCTURE OF EVOLUTIONARY THEORY