CHAPTER XIV 
FUNDAMENTAL PROBLEMS IN RELATION TO VARIATION 
AND HEREDITY 
Fundamental difficulties and objections — Mr. Herbert Spencer’s factors 
of organic evolution — Disuse and effects of withdrawal of natural 
selection—Supposed effects of disuse among wild animals—Difficulty 
as to co-adaptation of parts by variation and selection—Direct action 
of the environment—The American school of evolutionists — Origin 
of the feet of the ungulates— Supposed action of animal intelligence — 
Semper on the direct influence of the environment — Professor Geddes’s 
theory of variation in plants—Objections 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 varia¬ 
tions—Weismann’s theory of heredity— The cause of variation — The 
11011 -heredity of acquired characters— The theory of instinct—Con¬ 
cluding 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 
