514 THE STRUCTURE OF EVOLUTIONARY THEORY
in excess of almost any other Darwinian change in nature. In evolutionary time,
Fisher laments, our social structures disintegrate rapidly; we had better pay heed:
"Civilized man, in fact, judging by the fertility statistics of our own time, is
apparently subjected to a selective process of an intensity approaching a
hundredfold the intensities we can expect to find among wild animals, with the
possible exception of groups which have suffered a recent and profound change in
their environment" (1930, p. 199).
J. B. S. HALDANE AND THE INITIAL PLURALISM
OF THE SYNTHESIS
Haldane purposely included a plural in the title of his book—The Causes of
Evolution (1932)—for he believed that nothing so encompassing could be so
unifactorial. But Haldane wrote his book in the tradition of restriction, primarily to
debunk Kellogg's triad of alternatives by showing the power of natural selection.
He states (p. v) that his book began as a series of lectures entitled "A
Reexamination of Darwinism," and he then announces his primary aim in the
preface (p. vi): "To prove that mutation, Lamarckian transformation, and so on,
cannot prevail against natural selection of even moderate intensity." (Haldane
treats the same subject more formally in the book's lengthy mathematical appendix,
thus uniting both the front and back matter for a single purpose.)
Haldane presents a conventional account of the revivification of Darwinism
and the rejection of alternatives. Darwinism had fallen on bad times before the
synthesis: "Criticism of Darwinism has been so thoroughgoing that a few
biologists and many laymen regard it as more or less exploded" (p. 32). The
Darwinian resurrection followed from the recognition that continuous, small-scale
variation could also claim a Mendelian basis (p. 71) and, especially, that tiny
selection pressures, working in a cumulative manner on such minor variations,
could effectively explain all evolution: "But however small may be the selective
advantage the new character will spread, provided it is present in enough
individuals of the population to prevent its disappearance by mere random
extinction.... An average advantage of one in a million will be quite effective in
most species" (1932, p. 100).
The development of mathematical population genetics establishes the
centerpiece of Darwinian revival. Haldane even begins the tradition of a founding
trinity in stating, however immodestly (p. 33): "I can write of natural selection with
authority because I am one of the three people who know most about its
mathematical theory."
However, in contrast to Fisher's quest for pervasive and abstract generality,
Haldane felt compelled to bring the smaller and more particular puzzles of natural
history under his theoretical umbrella. Here he allows a substantial range of
exceptions to Darwinism, albeit at subsidiary frequency—thus illustrating the
predominant pluralism of the early synthesis. Haldane rejects Lamarckism outright,
as contrary in principle to the known workings of inheritance. But, in a remarkable
passage, he finds some space, in chinks and