The Fruitful Facets of Galton's Polyhedron 387
pattern for Columba livia; the former was supposed to be a variation arising
there from, a frequent occurrence but of no importance. Just the contrary is
true; the chequered pigeon represents the more ancient type, from which the
two-barred type has been derived. ... The direction of evolution in pattern in
the rock pigeons has been from a condition of relative uniformity to one of
regional differentiation (1919, p. 49).Whitman's inversion of Darwin's sequence lay embedded within a theory of
evolutionary change that Darwin would also have rejected. Whitman based his
reversal on a more general concept of directional change in coloration from an
initial homogeneity (checkers on all wing feathers) towards regional differentiation
(elimination of checkers over most of the wing, with strengthening and
coalescence to bars at the distal edge. The bars form by enlargement and alignment
of checkers on adjacent feathers; a bar, in other words, arises from a row of
checkers that "flow together in a single band"— Whitman, 1919, p. 99).
Whitman then expanded his sequence of reduction plus regional
differentiation beyond the patterns of domesticated pigeons to identify an
ineluctable, orthogenetic tendency in the entire family Columbidae (with the
portion displayed by domestic pigeons as just a small part of a much more
extensive trend). He identified a prototype for the entire series in the "turtle-dove"
pattern, a homogeneous field of feathers, each with a dark spot in the center (see
Fig. 5-8): "This ancestral mark is a dark spot rilling the whole central part of the
feather, leaving only a narrow distal edge of a lighter color. This mark is still well
preserved in some of the old world turtledoves—best in the Oriental turtledove of
China and Japan. The chequer of Columba livia differs from the dark center of
Turtur orientalis only in form and in having a lateral position" (1919, p. 23).
From this beginning, the trend moved towards an inexorable end, guided