INTRODUCTION 9 



and nature and to adopt the same methods in dealing 

 with both. 



Before this result could be attained, the partisans 

 of transformation had to overcome a formidable op- 

 position; if the controversy on the origin of species 

 assumed such a bitter character it was because the 

 close of the debate was expected to settle the ques- 

 tions relative to the origin of man. 



That was the burning, the painful issue between 

 the two camps and that is why the transformists had 

 to pay so dearly for their victory. Their victory, 

 however, was definitive; man was to be considered 

 henceforth as the last link in the evolution of the an- 

 imal world, produced by causes as natural as those 

 which determined the appearance of other species. 



The victorious party soon faced new problems 

 arising from the very problems which had just been 

 solved, for instance, the origin of our psychical life. 

 The new theories endeavoured to relate psychical phe- 

 nomena with those observable in the physiology of 

 the nervous system and especially of the brain. Since 

 the human brain to-day is the result of the gradual 

 development of the same organ in the individual se- 

 ries, why should not the human mind be the result of \ 

 the perfect development of animal psychology? 



This method of approaching the subject conflicted 

 with all accepted ideas, with all the beliefs which 

 not only appeared undeniable, but were held to be 



