THE DERIVATIVE ORIGIN OF THE HUMAN MIND. 793 



question is neither a superficial nor an easy one. I shall, however, 

 endeavor to examine it with as little obscurity as possible, and 

 also, I need hardly say, with all the impartiality of which I am 

 capable.* 



It will be remembered that in the introductory chapter of my 

 previous work f I have already briefly sketched the manner in 

 which I propose to treat this question. Here, therefore, it is 

 sufficient to remark that I began by assuming the truth of the 

 general theory of descent so far as the animal kingdom is con- 

 cerned, both with respect to bodily and to mental organization ; 

 but in doing this I expressly excluded the mental organization of 

 man, as being a department of comparative psychology with refer- 

 ence to which I did not feel entitled to assume the principles of 

 evolution. The reason why I made this special exception, I suffi- 

 ciently explained; and I shall therefore now proceed, without 

 further introduction, to a full consideration of the problem that 

 is before us. 



First, let us consider the question on purely a priori grounds. 

 In accordance with our original hypothesis — upon which all nat- 

 uralists of any standing are nowadays agreed — the process of 

 organic and of mental evolution has been continuous throughout 

 the whole region of life and of mind, with the one exception of 

 the mind of man. On grounds of analogy, therefore, we should 

 deem it antecedently improbable that the process of evolution, 

 elsewhere so uniform and ubiquitous, should have been inter- 

 rupted at its terminal phase. And looking to the very large 

 extent of this analogy, the antecedent presumption which it raises 

 is so considerable, that in my opinion it could only be counter- 

 balanced by some very cogent and unmistakable facts, showing a 

 difference between animal and human psychology so distinctive 

 as to render it in the nature of the case virtually impossible that 

 the one could ever have graduated into the other. This I posit as 

 the first consideration. 



Next, still restricting ourselves to an a priori view, it is unques- 

 tionable that human psychology, in the case of every individual 

 human being, presents to actual observation a process of gradual 

 development, or evolution, extending from infancy to manhood ; 

 and that in this process, which begins at a zero level of mental 



* It is perhaps desirable to explain from the first that by the words " difference of 

 kind," as used in the above paragraph and elsewhere throughout this treatise, I mean differ- 

 ence of origin. This is the only real distinction that can be drawn between the terms " dif- 

 ference of kind " and " difference of degree " ; and I should scarcely have deemed it worth 

 while to give the definition, had it not been for the confused manner in which the terms 

 are used by some writers — e. g.. Prof. Sayce, who says, while speaking of the development 

 of languages from a common source, " differences of degree become in time differences of 

 kind " (" Introduction to the Science of Language," ii, 309). 



f " Mental Evolution in Animals." 



