e itself to the fate of being _a
priori_ rejected by science as unjustified, and of being _a posteriori_
confuted by facts--a fate which it has richly and clearly experienced in
the first half of our century. But the discussion of the metaphysical way
does not belong to the present purely scientific part of our investigation;
it will, however, be shortly taken up again in Book II. The other way, the
scientific-empirical, will have to be looked upon as correct when it can
show the impelling forces of development in such powers and laws as are
either still active to-day or at least have their points of connection in
powers and laws active to-day. Such an attempt is the selection theory. We
have already in Chap. II, Sec. 1 and 2, given an outline of this theory, and
have only yet to discuss its present state of tenability.

Sec. 3. _The Theory of Selection._

The selection theory also is not entirely without support in the realm of
observed facts. How simply it explains the fixedness of the differences of
closely related species arising from their geographical and climatical
home! how simply the similarity of the color of many animals from the color
of their abode, through which they have protection against persecution! how
simply the so-called _mimicry_--_i.e._, the similarity of certain species
in form and color with form and color of entirely different species in the
midst of which they live, a similarity which often gives them protection
against persecution! The best known examples of this, in our regions, are
the spinning caterpillars, which in a state of rest look strikingly like a
twig of a tree or a shrub on which {101} they live. In other regions there
is a multitude of the most striking freaks of nature of this kind--for
instance, butterflies and other insects, which at rest look like the leaves
of plants under which they live; butterflies living among other butterflies
which, by an offensive odor, are protected against persecution, and
although they are themselves a favorite food for birds, carrying the form
and color of that badly-smelling family of butterflies. We can also add the
orchideae, and their resemblance to bees, flies, butterflies, spiders, etc.
A. R. Wallace and Darwin themselves recur often to these striking
appearances.

But herewith we have mentioned nearly every support which the selection
theory has on the ground of observed facts. More numerous and more weighty
are the objections to it. First