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7

The Synthesis

and Species

First, then, we have the problem involved in the origin of species. As a pre-

liminary to that, logic demands that we should define the term. It may be that

logic is wrong, and that it would be better to leave it undefined, accepting the

fact that all biologists have a pragmatic idea at the back of their heads. It may

even be that the word is undefinable. However, an attempt at a definition will

be of service in throwing light on the difficulties of the biological as well of the

logical problems involved.

Ronald Aylmer Fisher^1

Ronald Fisher and Wild-Type Species

Ronald A. Fisher is famous as the founder of the modern synthesis between Mendelian
genetics and Darwinian natural selection. The Genetical Theory of Natural Selection
is a seminal work that introduced mathematical models to genetics and selection,
and while often cited is rarely quoted.^2 But Fisher addressed a number of questions
in that book, including a rarely mentioned discussion about eugenics (Fisher was
in favor of a form of eugenics, and chapters 8 through 12 are an argument for it),
and one of these questions, almost parenthetically, is about species in the context of
sexual and asexual reproduction.
The tradition in British evolutionary biology since Fisher has, on the whole, tended
to treat species as names of convenience for communication, in the style of Darwin of
the Origin, and of Locke. It is therefore somewhat surprising to note that Fisher had
a realist approach to species, and one that predated the 1935 article by Dobzhansky
that is widely seen as kicking off the species debate of the modern era. Fisher says
of species that

[t]he genetical identity in the majority of loci, which underlies the genetic variability

presented by most species, seems to supply the systematist with the true basis of his

concepts of specific identity or diversity.^3

Sexual species are, in fact, the “wild type”—the sum of all the genes in any spe-

cies the great majority of which are uniform:

(^1) Huxley 1940, 154.
(^2) Fisher 1930.
(^3) Fisher 1930, 138.