ons to the theory--On the origin
of spines--Variation and selection overpower the effects of use
and disuse--Supposed action of the environment in imitating
variations--Weismann's theory of heredity--The cause of
variation--The non-heredity of acquired characters--The theory
of instinct--Concluding remarks.

Having now set forth and illustrated at some length the most important
of the applications of the development hypothesis in the explanation of
the broader and more generally interesting phenomena presented by the
organic world, we propose to discuss some of the more fundamental
problems and difficulties which have recently been adduced by eminent
naturalists. It is the more necessary to do this, because there is now a
tendency to minimise the action of natural selection in the production
of organic forms, and to set up in its place certain fundamental
principles of variation or laws of growth, which it is urged are the
real originators of the several lines of development, and of most of the
variety of form and structure in the vegetable and animal kingdoms.
These views have, moreover, been seized upon by popular writers to throw
doubt and discredit on the whole theory of evolution, and especially on
Darwin's presentation of that theory, to the bewilderment of the general
public, who are quite unable to decide how far the new views, even if
well established, tend to subvert the Darwinian theory, or whether they
are really more than subsidiary parts of it, and quite powerless without
it to produce any effect whatever.

The writers whose special views we now propose to consider are: (1) Mr.
Herbert Spencer, on modification of structures arising from modification
of functions, as set forth in his _Factors of Organic Evolution_. (2)
Dr. E.D. Cope, who advocates similar views in detail, in his work
entitled _The Origin of the Fittest_, and may be considered the head of
a school of American naturalists who minimise the agency of natural
selection. (3) Dr. Karl Semper, who has especially studied the direct
influence of the environment in the whole animal kingdom, and has set
forth his views in a volume on _The Natural Conditions of Existence as
they Affect Animal Life_. (4) Mr. Patrick Geddes, who urges that
fundamental laws of growth, and the antagonism of vegetative and
reproductive forces, account for much that has been imputed to natural
selection.

We will now endeavour to ascertain what are