rlying Platonism in this magical physics is obvious, since the
natures that Aristotle made to rule the world were eternal natures. An
individual might fail to be a perfect man or a perfect monkey, but the
specific human or simian ideal, by which he had been formed in so far as
he was formed at all, was not affected by this accidental resistance in
the matter at hand, as an adamantine seal, even if at times the wax by
defect or impurity failed to receive a perfect impression, would remain
unchanged and ready to be stamped perpetually on new material.

[Sidenote: If species are evolved they cannot guide evolution.]

The contrast is obvious between this Platonic physics and a naturalism
like that of Darwin. The point of evolution, as selection produces it,
is that new species may arise. The very title of Darwin's book "The
Origin of Species" is a denial of Aristotelianism and, in the pregnant
sense, of evolution. It suggests that the type approached by each
generation may differ from that approached by the previous one; that
not merely the degree of perfection, but the direction of growth, may
vary. The individual is not merely unfolded from an inner potentiality
derived from a like ancestor and carrying with it a fixed eternal ideal,
but on the contrary the very ground plan of organisation may gradually
change and a new form and a new ideal may appear. Spontaneous
variations--of course mechanically caused[C]--may occur and may modify
the hereditary form of animals. These variations, superposed upon one
another, may in time constitute a nature wholly unlike its first
original. This accidental, cumulative evolution accordingly justifies a
declaration of moral liberty. I am not obliged to aspire to the nature
my father aspired to, for the ground of my being is partly new. In me
nature is making a novel experiment. I am the adoring creator of a new
spiritual good. My duties have shifted with my shifting faculties, and
the ideal which I propose to myself, and alone can honestly propose, is
unprecedented, the expression of a moving existence and without
authority beyond the range of existences congruous with mine.

[Sidenote: Intrusion of optimism.]

All that is scientific or Darwinian in the theory of evolution is
accordingly an application of mechanism, a proof that mechanism lies at
the basis of life and morals. The Aristotelian notion of development,
however, was too deeply rooted in tradition for it to disappear at a
br