The Fruitful Facets of Galton's Polyhedron 449
for Darwin's ingenious theory. Chance there is, but no more than anywhere
else. It is not by mere chance that the variations move in the required
direction. They do go, according to Darwin's view, in all directions, or at
least in many. If these include the usual ones, and if this is repeated a
number of times, cumulation is possible; if not, there is simply no
progression, and the type remains stable through the ages. Natural selection
is continually acting as a sieve, throwing out the useless changes and
retaining the real improvements. Hence the accumulation in apparently
predisposed directions, and hence the increasing adaptations to the more
specialized conditions of life (1905, p. 572).De Vries also recognizes that species selection must include two components,
corresponding to birth and death biases in conventional organismic selection
(1909a, volume 1, p. 200, and volume 2, p. 660): Species selection will favor those
lineages that (1) produce more elementary species by mutation (birth bias), and (2)
generate phenotypes fortuitously adapted to changing local conditions (persistence
bias).
The need for strong birth biases, combined with the central claim (see p. 435)
that periods of mutability affect only a few species (and for a very short time
relative to their geological longevity), led de Vries to embrace the importance and
near universality of long-term stasis within species—an argument strikingly
isomorphic with the apparatus that we introduced much later in developing
punctuated equilibrium (Eldredge and Gould, 1972; Gould and Eldredge, 1977,
1993 —and, again, much to my chagrin for not knowing about de Vries' earlier
version. The two accounts invoke entirely different principles of saltational vs.
allopatric speciation, but the two arguments still employ an isomorphic logic).
De Vries cites several supports for the empirics of stasis: the ability of
systematists to define most taxa unambiguously; the persistence of identical
phenotypes for centuries in populations that have become widely isolated (1909a,
volume 1, p. 206); geological persistence through such epochs of extensive
climatic change as ice ages (1905, p. 696); documented longevity of many species
through several geological periods (1905, pp. 698-699). De Vries then chides
Darwinians for asserting imperceptible transmutation in the face of manifest,
documented constancy. Darwinians have been driven to this inconsistency, de
Vries asserts, by the gradualistic implications of their theory, but a more accurate
view of evolutionary mechanisms affirms stasis as an expectation, not an
embarrassment to be ignored, or explained away by appeals to an imperfect fossil
record:
Many facts plead in favor of the constancy of species. This principle has
always been recognized by systematists. Temporarily the current form of
the theory of natural selection has assumed species to be inconstant, ever
changing and continuously improved and adapted to the requirements of the
life conditions. The followers of the theory of descent believed that this
conclusion was unavoidable and were induced to deny the manifest fact
that species are constant entities. The mutation theory gives a clue to