egg, and the term still carries
with it something of its original significance.

Naegeli's speculation written several years after Darwin's "Origin of
Species" may be taken as a typical case. Naegeli thought that there exists
in living material an innate power to grow and expand. He vehemently
protested that he meant only a mechanical principle but as he failed to
refer such a principle to any properties of matter known to physicists and
chemists his view seems still a mysterious affirmation, as difficult to
understand as the facts themselves which it purports to explain.

Naegeli compared the process of evolution to the growth of a tree, whose
ultimate twigs represent the living world of species. Natural selection
plays only the role of the gardener who prunes the tree into this or that
shape but who has himself _produced_ nothing. As an imaginative figure of
speech Naegeli's comparison of the tree might even today seem to hold if we
substituted "mutations" for "growth", but although we know so little about
what causes mutations there is no reason for supposing them to be due to an
inner impulse, and hence they furnish no justification for such a
hypothesis.

In his recent presidential address before the British Association Bateson
has inverted this idea. I suspect that his effort was intended as little
more than a _tour de force_. He claims for it no more than that it is a
possible line of speculation. Perhaps he thought the time had come to give
a shock to our too confident views concerning evolution. Be this as it may,
he has invented a striking paradox. Evolution has taken place through the
steady loss of inhibiting factors. Living matter was stopped down, so to
speak, at the beginning of the world. As the stops are lost, new things
emerge. Living matter has changed only in that it has become simpler.

NATURAL SELECTION

_Darwin_

Of the four great historical speculations about evolution, the doctrine of
Natural Selection of Darwin and Wallace has met with the most widespread
acceptance. In the last lecture I intend to examine this theory critically.
Here we are concerned only with its broadest aspects.

Darwin appealed to _chance variations_ as supplying evolution with the
material on which natural selection works. If we accept, for the moment,
this statement as the cardinal doctrine of natural selection it may appear
that evolution is due, (1) _not_ to an _orderly_ response of the organism
to its environm