e of its articulation with the foot, which seems to assist in
securing the forward direction taken by it in later life.

[2] _Man's Place in Nature_, p. 65.

VI.

ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS.

There are two or three arguments of a somewhat weighty character, which
do not fall under any of the previous headings, but which we must not on
this account neglect.

1. It is justly deemed a substantiation of a scientific theory if it is
found to furnish an explanation of other classes of phenomena than those
for the explanation of which it was first devised. And this is the case
with the theory of natural selection in the region of psychology. The
theory was first devised to explain the facts of biology, and proving
so successful in that region, Mr. Darwin proceeded to test it in the
region of psychology. The result has been to show that large classes of
phenomena in this region which were previously unaccountable become
fully intelligible. This is especially the case with the phenomena of
instinct, and in a lesser degree with those of reason and conscience.
For the theory shows that if structures admit of being moulded to their
special uses by natural selection, the same must be true of instincts;
and it is found an easy matter to understand how, by seizing upon and
fixing, through hereditary beneficial variations of habit (whether
instinctive or intelligent), natural selection is as competent to
fashion the mental structure of an animal as it is to shape its bodily
structure into agreement with the external conditions of life. Thus the
whole philosophy of animal intelligence is greatly elucidated, and this
fact may justly be regarded as lending much additional credence to the
theory.

Again, by observing that sympathy and the social instincts generally are
developed to a large extent in many of the lower animals, and
particularly so in the quadrumana, the theory of natural selection is
provided with a reasonable basis for furnishing a scientific explanation
of the moral sense in man; and by observing that many of the lower
animals are capable of drawing simple inferences, the theory is likewise
able to explain the development of reason. So that in the province of
human psychology no less than in that of animal, the theory of natural
selection, in showing itself competent to explain much which is
otherwise inexplicable, is seen to derive a large additional measure of
argumentative support