MENTAL EVOLUTION 405 



tinguished with respect to music, literature, engineering, or warfare. 

 But there is nothing more wonderful in this than in the fact that 

 some part of a structure (e.g. a nose) may be relatively more 

 developed in one man than in another. Men often differ very 

 greatly in mental capacity, in innate power of making this or that 

 acquirement, and doubtless these mental differences are associated 

 with innate cerebral peculiarities, and tend, therefore, to be trans- 

 mitted to offspring; but it must be borne in mind that mental 

 differences need not imply correspondingly great cerebral 

 differences. When we attempt to estimate the latter by means of 

 the former, we examine them, as it were, through a magnifying 

 glass. The amount of nervous tissue in the brains of ants is very 

 small and the differences apparently are not very great, yet the 

 species differ vastly in their mental characters. Small cerebral 

 variations, therefore, may imply great psychological differences. 



669. None of the objections by which it was sought to contro- 

 vert the doctrine of man's mental evolution from lowerltypes could 

 have been maintained had the faculties (mathematical, devotional, 

 musical, and the like) concerning which controversy raged been 

 traced to their true source, memory. The evolution of memory 

 can be traced with the same degree of certainty as that of brain or 

 any other physical structure ; but I think I am right in saying 

 that hitherto no one has attempted to trace it. Its importance 

 has not been realised ; and only very scanty space is devoted to 

 it in standard works on evolution. The root of the mischief has 

 lain in the initial failure to note the real nature of the difference 

 between ' inborn ' and * acquired ' characters, and to compare the 

 parts they have played in evolution and development. Acquire- 

 ments, as I say, have been regarded as transient unimportant 

 traits, mere accidents, appearing in one generation and disappear- 

 ing in the next. Some attention, indeed, has been given to the 

 faculty of growth under the stimulus of injury (regeneration), but 

 wonderfully little has been attracted by the more important faculty 

 of growth under the stimulus of use and experience. 1 



670. The older students of psychological evolution supposed 

 that memory was an invariable accompaniment of consciousness 

 and therefore had no notion that it was a late and high product 

 of evolution. Darwin, as far as I have been able to ascertain, 

 devotes only one short paragraph to it, in which he merely relates 

 three incidents which tend to show that memory is present in 

 baboons, dogs and cats. 2 He discusses, however, at greater length, 



1 See 20, et seq. a D escen t of Man, p. 112. 



