MENTAL ADAPTATION 325 



variations, are not necessarily adaptations, but they are the 

 materials out of which nature manufactures adaptations. The 

 constant occurrence of them is an adaptation. Similarly, the 

 minds of animals are compounded of characters sense-impres- 

 sions, emotions, memory, and the like. Doubtless, individuals and 

 races differ, on the average, as much in mind as in body ; yet, here 

 again, the older and the more important, the specific or varietal 

 characters, the ' faculties,' are all or almost all adaptations. We 

 can think of no animal that affords evidence of possessing mind, 

 but we find that it is as certainly adapted mentally as physically 

 to its environment. For example, human sense-impressions, 

 emotions, instincts, and memory all fulfil this function. Therefore, 

 when studying mind as when studying body, we must ever keep 

 this great truth of adaptation before us. The facts are such, that 

 if our hypotheses, our interpretations of the facts, do not accord 

 with it, they are certainly erroneous. 1 



548. We saw that, when the whole of the facts are taken into 

 account, only two hypotheses of the causation of physical adaptation 

 are conceivable, or at any rate have been conceived, with any 

 degree of clearness miracle, and natural selection. This is not less 

 true of mind. We are bound in science not to appeal to the 

 supernatural till it has been demonstrated that natural explana- 

 tions are inadmissible. Nevertheless, some writers, even amongst 

 those who believe that the human body has evolved under the 

 action of Natural Selection, have been inclined to attribute to 

 mind a supernatural origin. On the one hand, they have insisted 

 that mind is so unique that it can have been evolved out of nothing 

 else in nature ; on the other, they have asked how it is possible 

 that such human * faculties ' as the mathematical, the musical, and 

 the devotional, which, seemingly, have never contributed to the 

 preservation of life, can have been brought into being by the 

 action of Natural Selection. Mind is certainly unique , neverthe- 

 less, as we shall see, this difficulty is not absolutely insurmount- 

 able. At any rate, it is not a unique difficulty. It is not a greater 

 difficulty than many others which science first ignores and then 

 proceeds as if they had been surmounted, leaving the consideration 

 of them to metaphysics, which seeks to be more thorough. 2 The 

 study of memory, intellectually the most important of all the 

 faculties, has been constantly neglected, and we shall find that 

 the evolution of this one character, easily explainable by the 

 theory of Natural Selection, furnishes the key to all such appa- 



1 See 616 and 648. * See 590. 



