PREFACE. 



THE two parts of which this Essay consists, originally 

 published in The Nineteenth Century for April and May 

 1886 respectively, now reappear with the assent of the 

 proprietor and editor of that periodical, to whom my 

 thanks are due for his courtesy in giving it. Some 

 passages of considerable length which, with a view to 

 needful brevity, were omitted when the articles first 

 appeared, have been restored. 



Though the direct bearings of the arguments contained 

 in this Essay are biological, the argument contained in its 

 first half has indirect bearings upon Psychology, Ethics, 

 and Sociology. My belief in the profound importance of 

 these indirect bearings, was originally a chief prompter 

 to set forth the argument; and it now prompts me to 

 re-issue it in permanent form. 



Though mental phenomena of many kinds, and especially 

 of the simpler kinds, are explicable only as resulting from 

 the natural selection of favourable variations ; yet there 

 are, I believe, still more numerous mental phenomena, 

 including all those of any considerable complexity, which 

 cannot be explained otherwise than as results of the 

 inheritance of functionally-produced modifications. What 

 theory of psychological evolution is espoused, thus depends 



