The Fruitful Facets of Galton's Polyhedron 401
category commanded his primary attention. Bateson devotes the entire text of
Materials to compiling examples of meristic variation. He planned, but never
wrote or even seriously began, a second volume on substantive variation.
(Bateson left a substantial legacy of biological terminology. He is best known,
of course, as the inventor of the word genetics, but Materials includes two new
terms of later importance—meristic for this general style of variation, and
homeosis for a subset that has since become central in modern evolutionary and
developmental biology; see Chapter 10.)
The evolutionary import of Bateson's book may be summarized in three
characteristic features of his argument for saltational variation and change, with a
subsequent fourth theme then centered upon his discussion of implications for
Darwinism.
NATURE OF THE EXAMPLES. Materials are, above all else, a compendium of
examples of discontinuous variation in meristic characters. Bateson begins with a
long sequence of chapters (pp. 87-422) on linear series, starting with arthropod
segments, moving through vertebrae and ribs, where Bateson presents the "type"
cases of homeosis, and proceeding to branchial openings, mammae, teeth and
digits. The second sequence of chapters (pp. 423-566) treats symmetrically
repeated structures under three headings: radial series, bilateral series, and
secondary symmetry and duplication. Although Bateson adopted a convention of
presenting facts in small type and interpretation in a larger font, he remained true
to his own version of the Kantian dictum that percepts without concepts are
blind—for even the factual small-type listings contain implicit interpretations for
his worldview, and against Darwin's.
As his primary theme, Bateson emphasizes a basic implication of meristic
variation. Segments must be conceptualized as discrete anatomical forms, and
supernumeraries (or deletions) are therefore usually complete (or entirely
suppressed). Half an added segment usually denotes a structural and functional
absurdity, in principle. Merism, by its very nature, implies discontinuity in
construction and change. Bateson writes, for example, about 12-jointed antennae
within a group of normally 11-jointed beetles:
Would it be expected that the longicorn Prionidae, most of which have the
unusual number of 12 antennary joints, did, as they separated from the
other longicorns which have 11 joints, gradually first acquire a new joint as
a rudiment which in successive generations increased? ... If anyone will try
to apply such a view to hundreds of like examples in arthropods, of
difference in number of joints and appendages of near allies ... he will find
that by this supposition of continuity in variation he is led into endless
absurdity. Surely it must be clear that in many such cases to suppose that
the limb came through a phase in which one of its divisions was half-made
or one of its joints half-grown, is to suppose that in the comparatively near
past it was an instrument of totally different character from that which it
has in either of the two perfect forms. But no such supposition is called for.
With evidence that transition of this nature