mparably greater bulk of investigation that followed the year 1859
was a continual increase of evidence in favour of the probability of
evolution, until now the whole scientific world, and the majority of
those who are unscientific, are content to accept evolution as the
only reasonable explanation of the living world. It is well to
remember that while Darwin, by bringing forward the theory of struggle
for existence and resulting survival of the fittest, was the actual
cause of the present assured position of evolution as a first
principle of science, it by no means follows that the survival of the
fittest has become similarly a first principle of science. At cross
roads a traveller may choose the right path from a quite
unsatisfactory reason. Darwin himself, in the act of bringing forward
his own theory of natural selection, admitted the possibility of the
co-operation of many other agencies in evolution, and at various times
during the course of his life he was inclined to attach, now more now
less, importance to these additional agencies. Huxley, as we shall
soon come to see, never wavered in his adhesion to the facts of
evolution after 1859; but, from first to last, regarded natural
selection as only the most probable cause of the occurrence of
evolution. Other naturalists, of whom the best-known are Weismann in
Germany, Ray Lankester in England, and W.K. Brooks in America, have
come to attach a continually increasing importance to the purely
Darwinian factor of natural selection; while others again, such as
Herbert Spencer in England, and the late Professor Cope and a large
American school, have advocated more and more strongly the importance
of what may be called the Lamarckian factors of evolution,--the
inherited effects of increased or diminished use of organs, the direct
influence of the environment, and so forth. From the fact that Darwin
has persuaded the world of the truth of evolution, evolution is often
called Darwinism; and in this historically just though scientifically
inaccurate sense of the term, Huxley was a strict Darwinian, a
Darwinian of the Darwinians. From the facts that, although natural
selection had been formulated by several writers before Darwin, and
had been simultaneously elaborated by Wallace and Darwin, the _Origin
of Species_ was the foundation of the modern acceptation of evolution,
and natural selection was the key-note of the origin of species,
natural selection may be called Darwini