508 THE STRUCTURE OF EVOLUTIONARY THEORY
denied evolutionary importance to mutations of large effect. At the same time, the
Mendelian explanation of this copious and small-scale variability left little scope
for orthogenesis. Darwinism surely welcomed this further Mendelian aid, for all
functionalist theories must try to smooth Galton's polyhedron.
Yet, while internalist theories endured a pronounced demotion during this
first phase of restriction, these alternatives to Darwinism did not suffer the
Lamarckian fate of complete dismissal in theory. Saltations could not be banished
or denied, but only declared unimportant in evolution. Orthogenesis could not be
overthrown in principle, for mutation pressure could conceivably boost the
frequency of alleles from within. Moreover, and more importantly as an enjoined
consequence of its own premises, population genetics had to acknowledge another
potentially substantial source for non-adaptive evolutionary change: the effects of
sampling errors, primarily in small populations.
Thus, the first phase of restriction invoked a fusion of Mendel and Darwin to
dismiss or downplay the traditional roster of alternatives to Darwinian
functionalism. But the resulting theory remained open and pluralistic in welcoming
all notions consistent with the new formulation of Mendelism. I shall devote the
rest of this section to three illustrations of the two key properties in this first phase
of the synthesis: (i) the revivified Darwinian core, and (ii) toleration of a broad
phenomenology, including substantial nonadaptation, so long as results could be
rendered by known genetic mechanisms. I will discuss the two most important
books of early population genetics: Fisher (1930) and Haldane (1932). Huxley's
compendium (1942) should be read as a transitional document, and may belong
more properly to the beginning of the second phase of hardening, but I include
Huxley's book here as a summation of early ideas in the Synthesis, if only for its
symbolic role in supplying the developing theory with a name.
R. A. FISHER AND THE DARWINIAN COREThe history of the Modern Synthesis holds special, one might almost say
inspirational, interest in the good fortune of its construction by such a fascinating
group of scientists—so different in personality, so diverse in philosophical attitude
amidst their defining agreement, and so brilliant. I experienced the great
intellectual privilege of knowing most of the second-phase founders— and I have
tried to understand the personal components of scientific greatness by, for
example, contrasting Dobzhansky's infectious enthusiasm with Mayr's fierce
commitment and encyclopedism. I have also pondered the intra-individual variety
in trying to square the warm and expansive humanism of Simpson's writing with
the irascibility of his personality.
The leaders of the first phase were equally fascinating and diverse. Their
differences have been discussed extensively, perhaps most cogently by one of the
actors himself (Wright, 1978). But R. A. Fisher holds a special status as author of
the movement's first major book (1930), and as the most thoroughgoing