Seeds of Hierarchy 217
at the same time, hierarchical selection does not merely extend Darwin's
exclusively organismal version in a simple, comfortable, or inexorable manner.
Rather, in fracturing Darwin's reliance on organisms as evolutionary agents, and in
rendering evolutionary variation and change by interaction among levels, the
theory of hierarchical selection introduces enough conceptual novelty, and
disperses enough inadequate orthodoxy, to rank as a new, and in some respects
radical, formulation, rather than a fully comfortable expansion.
Kellogg also grasped the weaknesses of germinal selection (which, of course,
would soon become irrelevant when the codification of Mendelism disproved
Weismann's conjecture about the physical mechanism of heredity). He asked
(1907, pp. 200-201) (1) why measured variation so often conformed to a normal
distribution if germinal selection could act so powerfully to promote directional
variation; (2) why species generally displayed such geological stability if germinal
selection provided such a strong mechanism for orthogenesis; and (3) why, if
determinants wage such constant battle, each against all others, severe deprivation
of food often produced a proportionately dwarfed organism, rather than a creature
lacking phenotypic expression for particular losing determinants in such intensified
struggle.
Weismann originally developed germinal selection to explain the
disappearance of degenerate organs, once he recognized that panmixia could only
yield a partial reduction. But he soon expanded the scope of his new theory into the
domain of positive selection as well, hoping to resolve thereby most of the
remaining dilemmas in classical Darwinism. The main promise of germinal
selection lay in its capacity to explain a phenomenon that could scarcely be more
inconvenient for Darwinism—directed variation. Darwin had emphasized the
"random" or undirected character of variational raw material as a prerequisite for
advocating natural selection as the cause of evolutionary change (see previous
discussion of this crucial principle on pp. 144-146). For directed variation, if
sufficiently powerful, would demote natural selection to a negative force for
eliminating the unfit (while the fit arise automatically by differential variation),
and a minor accelerator of trends originating for internal reasons (since random
mortality can sustain an evolutionary direction imparted by biased variation).
But germinal selection could now explain directed variation by differential
survival of struggling components within germ cells. Weismann therefore made a
sweep through evolutionary problems that might be resolved by his new and
selectionist theory of directed variation. In his original formulation of 1896,
Weismann identified three possible roles for germinal selection in positive
adaptation.
- Fleeming Jenkin (1867) had troubled Darwin with his analogy of potential
variation within a species to a rigid glass sphere. Selection could be effective along
any radius, but the movement of a modal form from center to surface exhausted all
possible variation, and positive selection must therefore damp itself to oblivion
before achieving any substantial change. But, Weismann argued, germinal
selection of successful determinants establishes a