The Fruitful Facets of Gabon's Polyhedron 435
an interesting later paper (de Vries, 1915), he tried to calculate the "coefficient of
mutation in Oenothera biennis" vs. O. Lamarckiana, concluding that the latter
species showed a 6 to 10 fold increase in mutability. De Vries attributed this
augmentation to a transition of one or more pangenes from stable to labile
positions—a pure speculation, but again consistent with his system and logic.)
Why only one? Did such rarity mean that de Vries had only discovered an
oddball, with no general message for evolution? De Vries recognized that such an
inference would destroy his system, and he therefore argued that all (or at least
many) species maintain potential for entering a "mutable period," but that very few
actually exist in such a state at any moment. (We know, after all, that most species
are stable in both current and paleontological perspective. If all lineages were as
mutable as O. Lamarckiana, we would never be able to designate Linnaean taxa,
for nature would then present a constantly changing and unbreakable continuum,
rather than a set of discrete and recognizable populations.) De Vries considered
himself fortunate that he had located even one species in such a state—for if
"mutable periods" constitute an almost incalculably tiny fraction of a species'
lifespan, the probability of finding any given species in such a state at any moment
becomes effectively zero. In trying to turn the tables on his adversaries, de Vries
argued that the discovery of even one case presupposes a generality for extremely
rare "mutable periods"—for if such mutability could be dismissed as simply
freakish and unique, he could not have expected to encounter even a single
example!
The view that it might be an isolated case, lying outside of the usual
procedure of nature, can hardly be sustained. On such a supposition it
would be far too rare to be disclosed by the investigation of a small number
of plants from a limited area. Its appearance within the limited field of
inquiry of a single man would have been almost a miracle... The mutable
condition ... must be a universal phenomenon, although affecting a small
proportion of the inhabitants of any region at one time: perhaps not more
than one in a hundred species, or perhaps not more than one in a thousand,
or even fewer may be expected to exhibit it (1905, p. 687).But why should a species enter a rare mutable period, and why should most
species be stable nearly all the time? What triggers a transition into this
exceedingly uncommon state of evolutionary promise? On this crucial point of his
entire system, de Vries fell almost eerily silent, for he could offer nothing precise.
He supposed (1909a, volume 1, pp. 206-207) that some external trigger of
environmental change—isolation by colonization of new areas, for example—must
initiate phyletic lability, but amounts and directions of mutation must be attributed
to internal states of pangenes (1905, p. 691). He offered a few general words about
pangenes becoming mutable, or moving to a position of high changeability, or
arising de novo with such a propensity. But he still couldn't cite anything physical,
or propose anything testable. De Vries' distress and unease about this crucial
subject even inspired a rare burst of