taxonomic characters adaptive, are equally mistaken with Bateson and his
followers, who regard all characters as mutational. No system of evolution
can be satisfactory unless it recognises that these two kinds of
characters are distinct and quite different in their nature. But it may be
asked, What objection is there to the theory of natural selection as an
explanation of adaptations? The objection is that all the evidence goes to
show that the necessary variations only arose under the given conditions,
and, further, that the actions of the conditions and the corresponding
actions of the organism give rise to stimuli which would produce somatic
modifications in the same direction as the permanent modifications which
have occurred. My view is, then, that specific characters are usually not
adaptations, that other characters of taxonomic value are some adaptive
and some unrelated to conditions of life, and that while non-adaptive
characters are due to spontaneous blastogenic variations or mutations,
adaptive characters are due to the direct influence of stimuli, causing
somatic modifications which become hereditary, in other words, to the
inheritance of acquired characters. It has become a familiar statement
that every individual is the result of its heredity and its environment.
The thesis that I desire to establish is that the heredity of each
individual and each type is compounded of variations or changes of two
distinct origins, one external and one internal; that is to say, of
variations resulting from changes originating in the germ-cells or
gametes, and of modifications produced originally in the soma by the
action of external stimuli, and subsequently affecting the gametes.

When we study the characters of animals in relation to sex we find that in
many cases there are conspicuous organs or characters present in one sex,
usually the male, which are absent or rudimentary in the other. The
conception of adaptation applies to these also, since we find that
characters consist often of weapons such as horns, antlers, and spurs,