202 THE STRUCTURE OF EVOLUTIONARY THEORY
Everything we see in animals is adaptation, whether of today, or of
yesterday... Every kind of cell... is adapted to absolutely definite and
specific functions, and every organ which is composed of these different
kinds of cells contains them in the proper proportions, and in a particular
arrangement which best serves the function of the organ... The organism
as a whole is adapted to the conditions of its life, and it is so at every stage
of its evolution" (1909, pp. 64-65. This statement comes from Weismann's
contribution to the "official" centennial celebration of Darwin's birth. Thus,
Weismann chose to honor Darwin by stressing panselection.)- Adaptation must be attributed either to some materialistic cause, or to
teleology (in the classic sense of spiritually directed purpose). The validity of
science depends upon our ability to supply explanations in the former mode. - Among materialistic proposals, only Lamarckism and natural selection can
explain adaptation—for adaptation is ubiquitous and clearly too complex to ascribe
to chance or to render as a side consequence of any process serving unrelated ends. - Since Lamarckism is logically impossible (under the doctrine of continuity
of germ-plasm), selection must be correct. To assert the Allmacht of selection, we
need no evidence beyond the disproof of Lamarckism. In fact, given the
complexities of nature, and our inability to reconstruct past conditions in detail, we
probably could not supply adequate direct evidence in any single case.
We accept it, not because we are able to demonstrate the process in detail,
not even because we can with more or less ease imagine it, but simply
because we must, because it is the only possible explanation that we can
conceive. For there are only two possible a priori explanations of
adaptations for the naturalist—namely, the transmission of functional
adaptations [i.e. Lamarckism] and natural selection; but as the first of these
can be excluded, only the second remains... We are thus able to prove by
exclusion the reality of natural selection, and once that is done, the general
objections which are based on our inability to demonstrate selection-value
in individual cases, must collapse, as being of no weight... It does not
matter whether I am able to do so or not, or whether I could do it well or ill;
once it is established that natural selection is the only principle which has to
be considered, it necessarily follows that the facts can be correctly
explained by natural selection (1893, pp. 336-337).In 1893, when he made this bold assertion to counter Spencer's claim for the
"inadequacy of natural selection," Weismann advocated a kind of double
exclusivity—for natural selection over Lamarckism, and for selection upon
organisms as the only mode of Darwinian action. As a terminological matter,
Weismann equated the general phrase "natural selection" with selection upon
organisms alone ("personal selection" in his words. For example, he wrote (1903,
vol. 2, p. 126): "It is upon this that the operation of natural selection,