INTRODUCTION 



of adapting their ideas and opinions to tlie facts. Sucli 

 argument leads naturally, even without any had intention, 

 away from the consideration of the opposing facts hack to 

 its starting-point — revolving in a circle and seeing nr.thin^' 

 which lies without the circle. This method is most surpris- 

 ing in those who, like A. Wagner, with his Lcivj of M'ujm- 

 fion, oppose the whole of Darwinism in order to put in its 

 place an explanation of evolution which can only find its phice 

 in Darwinism itself as a suhordinate of that theorv. Isolation 

 in space, regarded hy Wagner as alone regulating the origin 

 of species, favours and promotes the separation of the gradu- 

 ally produced diverse forms into species ; hut apart from the 

 truth that it does not alone explain the separation, its 

 influence cannot possihly he put in the place of that of 

 the principle of utility. 



The effective influence is not necessarily single — many 

 can be effective together. 



On this standpoint I have placed myself in my inquiries 

 from the first, and their course and their results have full}- 

 justifled me. 



On account of the relations which they bear to others, I 

 have repeated some of the facts already published by me 

 which serve as the foundation of my theory. The last sec- 

 tions of this book are specially devoted to such facts. 



It happens that my views on the question before us do not 

 agree with those of some of my valued friends and honoured 

 teachers, and if I am to uphold my own convictions I must 

 endeavour to refute theirs. 



As this opposition is little pleasing to myself, I am con- 

 vinced that my frank advocacy of scientific opinions will 

 neither by those who are aware of this personal relationship, 

 nor by those who are immediately affected, be stigmatised 

 as unfriendly and ungrateful. 



