INTRODUCTION. 19 



investigations constantly carried on which add data 

 to the question tacitly assumed. We find many 

 discussions as to which of the various theories of 

 evolution is the nearest the truth ; but it is very 

 seldom we find in scientific literature any discussion 

 as to the truth of the theory. Indeed, the study of 

 biology to-day assumes evolution as its foundation. 

 Whether a right or wrong method of study, it has 

 proved to be a necessity, and will at all events 

 serve to indicate how firmly the theory has become 

 rooted in modern science. Unless there is a marked 

 change in the tendency of thought, it is a safe pre- 

 diction that a few years more will see it a universal 

 conclusion of science. The question is, however, 

 still open to investigation, and, as we shall see, 

 there are still many difficulties which have not been 

 cleared away. There are still obstacles to be over- 

 come before the theory can be regarded as positively 

 settled. 



Among students of mental science, the term 

 evolution seldom has the same meaning that has 

 been indicated above. Their whole line of thought 

 is different, and they cannot, therefore, consider the 

 question as a purely scientific subject. In their 

 minds, evolution has more meaning than it has 

 among natural scientists. It is frequently made to 

 include certain metaphysical conceptions of the 

 meaning of the individual life ; the significance of 

 reproduction in general, as well as of the origin of 

 matter and force ; all questions of the greatest sig- 

 nificance, and, perhaps, rightly included in a philo- 

 sophical definition of evolution. But these ideas 



