been a process of descent with modification. If the animals and plants
whose remains are preserved as fossils, or at any rate forms closely
related to these, were not the ancestors of existing forms, there are only
two other possibilities: either the existing forms came into existence by
new creations after the older forms became extinct, or the ancestors of
existing forms, although they coexisted with the older forms, never left
any fossil remains. Each of these suppositions is incredible.

In view of these plain facts and their logical conclusion it is curious to
notice how Darwin in his _Origin of Species_ constantly mingles together
arguments to prove the proposition that evolution has occurred, that the
structure and relations of existing animals can only be explained by
descent with modification, with arguments and evidence in favour of
natural selection as the explanation and cause of evolution. In the great
controversy about evolution which his work aroused, the majority of the
educated public were ultimately convinced of the truth of evolution by the
belief that a sufficient cause of the process of change had been
discovered, rather than by the logical conclusion that the organisms of a
later period were the descendants of those of earlier periods. Even at the
present day the theory of natural selection is constantly confused with
the doctrine of evolution. The fact is that the investigation of the
causes of evolution has been going on and has been making progress from
the time of Darwin, and from times much earlier than his, down to the
present day.

Bionomics show that every type must be adapted in structure to maintain
its life under the conditions in which it lives, the primary requirements
being food and oxygen. Every animal must be able to procure food either of
various kinds or some special kind--either plants or other animals; it may
be adapted to feed on plants or to catch insects or fish or animals