Seeds of Hierarchy 219
fishes that have migrated into dark caves, organismal selection against eyes must
lead to differential survival of animals with weakened determinants for these
organs. Once debilitated, these determinants continue to lose battles of germinal
selection, and phenotypic expression sinks below the threshold that organismal
selection could regulate: "In short, only by this means are the determinants of the
useless organ brought upon the inclined plane, down which they are destined
slowly but incessantly to slide towards their complete extinction" (1896, p. 25).
The case for synergism becomes even clearer when selection acts for the
increasing complexity of an organ—for the two levels need not engage in a relay,
but may now work continuously together in the same direction. Organismal
selection favors a stronger part, thereby preserving organisms with more powerful
determinants for the part, and unleashing a necessarily synergistic germinal
selection: "As soon as personal selection favors the more powerful variations of the
determinant ... at once the tendency must arise for them to vary still more strongly
in the plus direction... From the relative vigor or dynamical status of the particles
of the germ plasm, thus, will issue spontaneously an ascending line of variation,
precisely as the facts of evolution require" (1896, p. 27).
Weismann explicitly identified this inherent and automatic synergism as a
major insight, and a logical completion of his argument for the Allmacht of
selection. Noting "the harmony of the direction of variation with the requirements
of the conditions of life" (1896, p. 38), Weismann continues: "The degree of
adaptiveness which a part possesses itself evokes the direction of variation of that
part. This proposition seems to me to round off the whole theory of selection and
to give to it that degree of inner perfection and completeness which is necessary to
protect it against the many doubts which have gathered around it on all sides like
so many lowering thunderclouds... The principal and fundamental objection that
selection is unable to create the variations with which it works, is removed by the
apprehension that a germinal selection exists." And, more succinctly for the
centennial of Darwin's birth, Weismann reduced this theme to a celebratory
aphorism (1909, p. 39): "Germinal selection supplies the stones out of which
personal selection builds her temples and palaces: adaptations"—thus
amalgamating the synergistic link of levels, the Allmacht of selection, and the
primacy of adaptation (as recorded in a metaphorical linkage with the noblest of
buildings, both spiritual and temporal).
Divergence as a Consequence of Natural Selection
Weismann had granted an important role to germinal selection in his initial
formulation, but he had not yet developed a full theory of hierarchy, for germinal
selection could only walk the same paths established by ordinary natural
selection—at most accelerating or intensifying the journey. But when Weismann
wrote the major book and summation of his later career, Vortrage iiber
Descendenztheorie (1902; English translation, 1903), he devoted two full chapters
to germinal selection and, without explicitly acknowledging the