402 THE STRUCTURE OF EVOLUTIONARY THEORY
may be discontinuously effected the difficulty is removed (1894, pp. 410-
411).Whereas this basic argument contravenes gradualism, a second implication
then disputes natural selection. Supposed anomalies of discontinuous variation
often seem no less structurally "perfect" than normal forms. Why, then, do we so
confidently ascribe the "normal" forms to long honing by natural selection working
upon continuous variation? Should we not rather conclude that, since normal and
anomalous variants may be equally well constructed, both categories arise by
internal regulation? Of roaches with four-jointed tarsi (instead of the normal five),
Bateson writes: *
The four-jointed tarsus occurring thus sporadically, as a variety, is not less
definitely constituted than the five-jointed type, and the proportion of its
several joints is not less constant. It is scarcely necessary to point out that
these facts give no support to the view that the exactness or perfection with
which the proportions of the normal form are approached is a consequence
of selection. It appears rather, that there is two possible conditions, the one
of five joints and the other with four, each being a position of organic
stability. Into either of these the tarsus may fall; and though it is still
conceivable that the final choice between these two may have been made
by selection, yet it cannot be supposed that the accuracy and completeness
with which either condition is assumed is the work of selection, for the
"sport" is as definite as the normal (1894, pp. 64-65).In a further move to complete the basic argument within a supposed
compendium of objectively listed facts, Bateson emphasizes homology between
the teratology of individuals in one population and the normal morphology of a
related species—with an obvious implication of transformation by saltational
variation. Fusion of bilaterally symmetrical organs in the mid line (or fission of
singletons into pairs on the antimeres) establishes a major class of cases:
A normally unpaired organ standing in the middle line of a bilateral sym-
metry may divide into two so as to form a pair of organs; and conversely, a
pair of organs normally placed apart from each other on either side of a
middle line may be compounded together so as to form a single organ in the
middle line. In animals and plants nothing is more common than for
different forms to be distinguished from each other by the fact that an organ
standing in the middle line of one is in another represented by*Note Bateson's use of the term "position of organic stability." Bateson here cites
Galton's phrase, borrowed from his passages on the polyhedron metaphor. Bateson uses
the phrase throughout his text, often with quotation marks to indicate its source. Thus,
Bateson clearly embraced, as did many of his contemporaries, Galton's doubled-edged
metaphor for formalism against pure Darwinian externalism—though Bateson
emphasized the facet flipping (saltational) rather than the inherently directional
(orthogenetic) theme of the metaphor.