2 22 THE STRUCTURE OF EVOLUTIONARY THEORY
"In one direction variation can be proved to go on without limit, and that is
downwards, as is proved by the fact of the disappearance of disused organs, for
here we have a variation-direction, which has been followed to its utmost limit, and
which is completely independent of personal selection; it proceeds quite
uninterfered with by personal selection, and is left entirely to itself" [Weismann's
italics] (1903, vol. 2, p. 129). At England's major centennial celebration of
Darwin's birth, Weismann presented an even stronger statement (1909, p. 38):
"Useless organs are the only ones which are not helped to ascend again by personal
selection, and therefore in their case alone can we form any idea of how the
primary constitutents behave, when they are subject solely to intragerminal forces."
Such independence of levels implies potential conflict, with stability achieved
through balance, or by the victory of one level. Natural selection, as a powerful
force operating directly on phenotypes, usually prevails in its own domain of
visible form. If germinal selection weakens a useful organ, natural selection can
intervene in an antagonistic mode (except in degeneration, where natural selection
ceases to act, and germinal selection reigns unchecked). "If a struggle for food and
space actually takes place, then every passive weakening must lead to a permanent
condition of weakness and a lasting and irretrievable diminution in the size and
strength of the primary constituent concerned, unless personal selection intervenes,
and choosing out the strongest among these weakened primary constituents, raises
them again to their former level. But this never happens when the organ has
become useless" (1903, vol. 2, p. 122).
Similarly, if germinal selection initiates an orthogenetic trend, natural
selection can impose a halt by eliminating organisms with traits exaggerated
beyond utility, thereby removing their positive determinants from the germinal
population. (This basic antagonism, Weismann finally concluded in his strongest
recognition of potential conflict between levels, may be virtually omnipresent in
nature, and therefore fundamental to evolution, because positive organismal
selection almost always elicits an upward trend in determinants by Weismann's
earlier argument for synergism. Most stable species may not be quiescent with
respect to selection, but balanced by a policing of germinal selection with
opportune removals based upon Darwinian organismal competition.) "In the
majority of cases the self-regulation which is afforded by personal selection will be
enough to force back an organ which is in the act of increasing out of due
proportion to within its proper limits. The bearers of such excessively increased
determinants succumb in the struggle for existence, and the determinants are thus
removed from the genealogical lineage of the species" (1903, vol. 2, p. 130).
But germinal selection can also triumph, and such victories may not be
infrequent in nature. All orthogenetic and nonadaptive traits may record the
potency of suborganismal processes in conflicts between levels of selection: "All
excessive or defective hereditary malformations may be referred to germinal
selection alone, that is, to the long-continued progressive or regressive variation of
particular determinant-groups in a majority of ids" (1903, vol. 2, p. 138).