decide which is to perish and which to survive? To use a phrase of
Romanes, can they have SELECTION-VALUE?

Darwin himself answered this question, and brought together many excellent
examples to show that differences, apparently insignificant because very
small, might be of decisive importance for the life of the possessor. But
it is by no means enough to bring forward cases of this kind, for the
question is not merely whether finished adaptations have selection-value,
but whether the first beginnings of these, and whether the small, I might
almost say minimal increments, which have led up from these beginnings to
the perfect adaptation, have also had selection-value. To this question
even one who, like myself, has been for many years a convinced adherent of
the theory of selection, can only reply: WE MUST ASSUME SO, BUT WE CANNOT
PROVE IT IN ANY CASE. It is not upon demonstrative evidence that we rely
when we champion the doctrine of selection as a scientific truth; we base
our argument on quite other grounds. Undoubtedly there are many apparently
insignificant features, which can nevertheless be shown to be adaptations--
for instance, the thickness of the basin-shaped shell of the limpets that
live among the breakers on the shore. There can be no doubt that the
thickness of these shells, combined with their flat form, protects the
animals from the force of the waves breaking upon them,--but how have they
become so thick? What proportion of thickness was sufficient to decide
that of two variants of a limpet one should survive, the other be
eliminated? We can say nothing more than that we infer from the present
state of the shell, that it must have varied in regard to differences in
shell-thickness, and that these differences must have had selection-value,
--no proof therefore, but an assumption which we must show to be
convincing.

For a long time the marvellously complex RADIATE and LATTICE-WORK skeletons