The Fruitful Facets of Gabon's Polyhedron 365
influence. Selection only sharpens the edge of success by eliminating the failures.
Thus we may compare the whole process of the modification of forms to
the results of the migration of the people over an extensive foreign territory.
Some tribes, not having the strength to follow, soon, others later, remain
behind; others again reach a distant goal. Some retain their characters in
their new home or strengthen them, even modify them by correlation,
others change under the influence of external conditions and adapt
themselves to the environment—all that is not sufficiently capable of
endurance is left lying by the way and perishes, and if the struggle for
existence is at all severe only the toughest of all survive (1890, p. 55).World of Mollusks Alpheus Hyatt: An Orthogenetic Hard Line from the
THE WORLD OF MOLLUSKS
Standard examples of orthogenesis all took the same form: paleontologically
based, and therefore temporally extensive, monotonic trends towards clearly
inadaptive features, leading inevitably to the extinction of the afflicted lineage.
Supposed "best cases" included the enlarging antlers of the "Irish Elk" (but see
Gould, 1974), the extended canines of saber-toothed cats, and the self-strangulation
of the oyster Gryphaea, as overcoiling of one valve clamped the other shut,
immuring the animal in its own shell (but see Gould, 1972).
These lurid stories, in their textbook versions, are the caricatures of a serious
non-Darwinian theory once quite popular among paleontologists from the late 19th
century through the 1930's: the idea that trends, though adaptively initiated, might
break from environmental control and run, inexorably along the same path,
eventually to extinction—if the proximal cause that originally responded to the
adaptive pressure became so entrenched that selection could no longer halt or
reverse the trend. W. D. Lang (1923), for example, proposed that an originally
adaptive increase in rates of shell secretion might become unreversible, leading to
Gryphaea's deathly dilemma: "These trends, even if at first encouraged by the
environment because they are of use to the organism, are soon out of the
environment's control; they are lapses which may overtake Ostrea [the supposed
ancestor of Gryphaea] at any moment of its evolution—trends which having once
started continue inevitably to the point when their exaggeration puts the organism
so much out of harmony with its environment as to cause its extinction." A. E.
Trueman, who had developed the empirical case for Gryphaea (1922), also
asserted the anti-Darwinian character of internally driven trends: "Excessive
development implies that the evolution was out of the control of the environment
and it may be presumed that some internal factor was responsible" (1940, p. 93).
Trueman proposed no mystical or vitalist explanation (as the standard caricature
maintains), but sought a cause consistent with modern genetics. (He suggested