al
location of growth-force by use; useless ones have been produced by
location of growth-force without the influence of use. Another element
which determines the direction of growth-force, and which precedes use,
is effort; and "it is thought that effort becomes incorporated into the
metaphysical acquisitions of the parent, and is inherited with other
metaphysical qualities by the young, which, during the period of growth,
is much more susceptible to modifying influences, and is likely to
exhibit structural change in consequence."[204]

From these few examples of their teachings, it is clear that these
American evolutionists have departed very widely from the views of Mr.
Darwin, and in place of the well-established causes and admitted laws to
which he appeals have introduced theoretical conceptions which have not
yet been tested by experiments or facts, as well as metaphysical
conceptions which are incapable of proof. And when they come to
illustrate these views by an appeal to palaeontology or morphology, we
find that a far simpler and more complete explanation of the facts is
afforded by the established principles of variation and natural
selection. The confidence with which these new ideas are enunciated, and
the repeated assertion that without them Darwinism is powerless to
explain the origin of organic forms, renders it necessary to bestow a
little more time on the explanations they give us of well-known
phenomena with which, they assert, other theories are incompetent to
grapple.

As examples of use producing structural change, Mr. Cope adduces the
hooked and toothed beaks of the falcons and the butcher-birds, and he
argues that the fact of these birds belonging to widely different groups
proves that similarity of use has produced a similar structural result.
But no attempt is made to show any direct causal connection between the
use of a bill to cut or tear flesh and the development of a tooth on the
mandible. Such use might conceivably strengthen the bill or increase its
size, but not cause a special tooth-like outgrowth which was not present
in the ancestral thrush-like forms of the butcher-bird. On the other
hand, it is clear that any variations of the bill tending towards a hook
or tooth would give the possessor some advantage in seizing and tearing
its prey, and would thus be preserved and increased by natural
selection. Again, Mr. Cope urges the effects of a supposed "law of polar
or centrifugal growth"