nced soul of the anthropoid ape, and, at a still
more remote period, from the cerebral functions of the older
vertebrates. The eighth chapter of the _Origin of Species_, which is
devoted to instinct, contains weighty evidence that the instincts of
animals are subject, like all other vital processes, to the general
laws of historic development. The special instincts of particular
species were formed by adaptation, and the modifications thus acquired
were handed on to posterity by heredity; in their formation and
preservation natural selection plays the same part as in the
transformation of every other physiological function. The higher moral
qualities of civilised man have been derived from the lower mental
functions of the uncultivated barbarians and savages, and these in
turn from the social instincts of the mammals. This natural and
monistic psychology of Darwin's was afterwards more fully developed by
his friend George Romanes in his excellent works _Mental Evolution in
Animals_ and _Mental Evolution in Man_.[150]

Many valuable and most interesting contributions to this monistic
psychology of man were made by Darwin in his fine work on _The Descent
of Man and Selection in Relation to Sex_, and again in his
supplementary work, _The Expression of the Emotions in Man and
Animals_. To understand the historical development of Darwin's
anthropology one must read his life and the introduction to _The
Descent of Man_. From the moment that he was convinced of the truth
of the principle of descent--that is to say, from his thirtieth year,
in 1838--he recognised clearly that man could not be excluded from its
range. He recognised as a logical necessity the important conclusion
that "man is the co-descendant with other species of some ancient,
lower, and extinct form." For many years he gathered notes and
arguments in support of this thesis, and for the purpose of showing
the probable line of man's ancestry. But in the first edition of _The
Origin of Species_ (1859) he restricted himself to the single line,
that by this work "light would be thrown on the origin of man and his
history." In the fifty years that have elapsed since that time the
science of the origin and nature of man has made astonishing progress,
and we are now fairly agreed in a monistic conception of nature that
regards the whole universe, including man, as a wonderful unity,
governed by unalterable and eternal laws. In my philosophical book
_Die Weltraetsel_