Characters which were not obviously adaptive were explained either by
correlation or by the supposition that they had a utility of which we
were ignorant. Darwin also admitted the direct action of conditions as a
subordinate factor.

Weismannism not only retained the principle of utility and selection, but
made it the only principle, rejecting entirely the action of external
conditions as a cause of congenital modifications, _i.e._ of characters
whose development is predetermined in the fertilised ovum. It is to
Weismann that we owe precise and definite conceptions, if not of the
nature of heredity, at least of the details of the process. From him we
learned to think of the ova or sperms, of the reproductive cells or
'gametes' of an individual, as cells which were from an early stage of
development distinguished from the cells forming the organs and tissues;
to regard the organism as consisting of soma on the one hand and gametes
on the other, both derived from the original zygote cell, not the gametes
from the soma. Weismann saw no possibility of changes induced by any sort
of stimulation in the soma affecting the gametes in such a way as to be
redeveloped in the soma of the next generation. He attributed variation
partly to the union of gametes containing various determinants, which he
termed amphimixis: this, however, would introduce nothing new. Then he
proposed his theory of germinal selection, determinants growing and
multiplying in competition, some perhaps disappearing altogether, though
this does not satisfactorily account for entirely new characters. With
Weismann, however, every species was a different adaptation, and natural
selection was the _deus ex machina_; to quote his own words, _Alles ist
angepasst_.

Romanes and other writers, on the other hand, had always maintained that
in many cases the constant peculiarities of closely allied species had no