Importance of small differences 25 
are augmented in the course of innumerable generations, because 
their possessors more frequently survive in the struggle for existence. 
(8) Selection-value of the initial steps. 
Is it possible that the significant deviations which we know as 
“individual variations” can form the beginning of a process of 
selection? Can they 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 in- 
significant 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 be- 
ginnings 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 thick- 
ness 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 of Radiolarians were regarded as a mere outflow 
of “Nature’s infinite wealth of form,” as an instance of a purely 
morphological character with no biological significance. But recent 
investigations have shown that these, too, have an adaptive signifi- 
cance (Hicker).: The same thing has been shown by Schiitt in regard 
to the lowly unicellular plants, the Peridineae, which abound alike 
on the surface] of the ocean and in its depths. “It has been shown 
