346 THE STRUCTURE OF EVOLUTIONARY THEORY
new system of stability; in other words, a "sport" comes suddenly into
existence.In Galton's own conception, the polyhedron embodies four major implications
that assert and codify the power of formalist constraint as an evolutionary agent of
change (not just an impediment), while controverting the essential Darwinian
claim that natural selection alone builds new forms in a creative and accumulative
fashion.
- Occasional large variations (sports) are more important for evolution than
omnipresent, normally distributed small variation. This substitution of big for
small forces a major compromise, and may even represent a fatal weakness, in
Darwin's theory of natural selection.
Galton first introduced his polyhedron to question Darwin's key claim for
insensible gradation in evolutionary continuity. (Galton, of course, did not deny
continuity, but he wished to substitute a series of jumps—facet flipping, if you
will—for Darwin's smoothness): "It is shown by Mr. Darwin, in his great theory of
'The Origin of Species,' that all forms of organic life are in some sense convertible
into one another, for all have, according to his views, sprung from common
ancestry.... Yet the changes are not by insensible gradations; there are many, but
not an infinite number of intermediate links; how is the law of continuity to be
satisfied by a series of changes in jerks?" (1884 edition, p. 369).
In a later article on "Discontinuity in evolution," Galton posed the
fundamental question of change in Darwin's favored style: "By what steps did A
change into B? Was it necessarily through the accumulation of a long succession of
alterations, individually so small as to be almost imperceptible, though large and
conspicuous in the aggregate, or could there ever have been abrupt changes?"
(1894, p. 363). Acknowledging the criterion of relative frequency for resolving
debates in natural history, Galton correctly notes that Darwin did catalog
exceptions, but only to log their peripheral character and to assert the domination
of gradualistic accretion by natural selection leading to adaptation:
Notwithstanding a multitude of striking cases of the above description
collected by Darwin, the most marked impression left on the mind by the
sum of all his investigations was the paramount effect of the accumulation
of a succession of petty differences through the influence of natural
selection. This is certainly the prevalent idea among his successors at the
present day, with the corollary that the Evolution of races and species has
always been an enormously protracted process. I have myself written many
times during the last few years in an opposite sense to this.Galton then strongly asserts that most evolutionary novelty, in opposition to
Darwin, probably arises per saltum: "Many, if not most breeds, have had their
origin in sports" (p. 365). Galton bases his rationale on the argument that
continuous, small-scale Darwinian variability, though omnipresent, cannot