CHAPTER XIY 



FUNDAIklENTAL 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 natiu-al 

 selection — Supposed eftects 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 

 non-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 ex2:)lanation 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 throAv doubt and discredit on the whole theory of 



