causes in organic nature.)

If the new science of evolution had done no more than this, every
thoughtful man would have to admit that it had accomplished an immense
advance in knowledge. It means that in the whole of philosophy that
tendency which we call monistic, in opposition to the dualistic, which
has hitherto prevailed, must be accepted.* (* Monism is neither purely
materialistic nor purely spiritualistic, but a reconciliation of these
two principles, since it regards the whole of nature as one, and sees
only efficient causes at work in it. Dualism, on the contrary, holds
that nature and spirit, matter and force, the world and God, inorganic
and organic nature, are separate and independent existences. Cf. The
Riddle of the Universe chapter 12.) At this point the science of human
evolution has a direct and profound bearing on the foundations of
philosophy. Modern anthropology has, by its astounding discoveries
during the second half of the nineteenth century, compelled us to take
a completely monistic view of life. Our bodily structure and its life,
our embryonic development and our evolution as a species, teach us
that the same laws of nature rule in the life of man as in the rest of
the universe. For this reason, if for no others, it is desirable, nay,
indispensable, that every man who wishes to form a serious and
philosophic view of life, and, above all, the expert philosopher,
should acquaint himself with the chief facts of this branch of
science.

The facts of embryology have so great and obvious a significance in
this connection that even in recent years dualist and teleological
philosophers have tried to rid themselves of them by simply denying
them. This was done, for instance, as regards the fact that man is
developed from an egg, and that this egg or ovum is a simple cell, as