INTRODUCTION 13 



heredity. The question of the possibility of the transmission 

 of acquired characters, of the determination of congenital 

 modifications by the direct influence of conditions, is a very 

 important one, and has been much discussed. But I wish to 

 draw attention to a mode of considering the subject which is 

 generally neglected, namely the inductive method. The 

 doctrine of evolution is an induction from the facts of 

 zoology ; in my opinion conclusions concerning the method 

 and the causes of evolution can also be obtained as inductions 

 from a sufficiently wide survey of the phenomena. 



Every one will admit without hesitation that all variations 

 must be due to causes. But according to the selectionists 

 the conditions of life are never the causes of hereditary varia- 

 tions. On this view, therefore, no modification which is 

 hereditary can have any essential or necessary relation to 

 the requirements of life. The fitness of a structure or struc- 

 tural mechanism for its function is thus originally accidental. 

 For example, the long legs of wading birds are suitable for 

 their habit of wading, but the habit of wading did not make 

 the legs long. Some individuals had longer legs than others, 

 and those which had the longest survived because the length 

 of their legs enabled them to wade. 



Romanes maintained with much truth that natural selec- 

 tion was a theory of the origin of adaptations, not necessarily 

 of the origin of species, but it is further necessary to realise 

 that it originates adaptations only in the sense of preserving 

 and combining the variations or modifications which occur, 

 and which happen to be advantageous. It may be said to 

 combine only in the sense of causing different variations in 

 the parents to be transmitted together to the offspring, and 

 of allowing new variations to occur only in the individuals 

 which have survived. 



It may be admitted that the first step of a modification 

 or organ having occurred, there is nothing impossible in the 



