8 INTRODUCTION. 



method of the process has been natural selection, or survival 

 of the fittest. If anyone grants this much, I further assume 

 that he must concede to me the fad, as distinguished from the 

 manner and history of Mental Evolution, throughout the whole 

 range of the animal kingdom, with the exception of man. I 

 assume this because I hold that if the doctrine of Organic 

 Evolution is accepted, it carries with it, as a necessary 

 corollary, the doctrine of Mental Evolution, at all events as 

 far as the brute creation is concerned. Eor throughout the 

 brute creation, from wholly unintelligent animals to the most 

 highly intelligent, we can trace one continuous gradation ; so 

 that if we already believe that all specific forms of animal 

 life have had a derivative origin, we cannot refuse to believe 

 that all the mental faculties which these various forms 

 present must likewise have had a derivative origin. And, as 

 a matter of fact, we do not find anyone so unreasonable as to 

 maintain, or even to suggest, that if the evidence of Organic 

 Evolution is accepted, the evidence of Mental Evolution, 

 within the limits which I have named, can consistently be 

 rejected. The one body of evidence therefore serves as a 

 pedestal to the other, such that in the absence of the former 

 the latter would have no locus standi (for no one could well 

 dream of Mental Evolution were it not for the evidence of 

 Organic Evolution, or of the transmutation of species) ; while 

 the presence of the former irresistibly suggests the necessity 

 of the latter, as the logical structure for the support of which 

 the pedestal is what it is. 



It will be observed that in this statement of the case I 

 have expressly excluded the psychology of man, as being a 

 department of comparative psychology with reference to 

 which I am not entitled to assume the principles of Evolu- 

 tion. It seems needless to give my reasons for this exclusion 

 Eor it is notorious that from the hour when Mr. Darwin and 

 Mr. Wallace simultaneously propounded the theory which 

 has exerted so enormous an influence on the thought of the 



