Characters, Hereditary and Acquired. 87 



as it may, at present there are only two hypo- 

 theses in the field whereby to account for the facts 

 of adaptive evolution. One of these hypotheses 

 is universally accepted, and the only question is 

 whether we are to regard it as alone sufficient to ex- 

 plain all the facts. The other hypothesis having been 

 questioned, we can test its validity only by finding 

 cases which it is fully capable of explaining, and 

 which do not admit of being explained by its com- 

 panion hypothesis. I have endeavoured to show 

 that we have a large class of such cases in the 

 domain of reflex action, and shall next endeavour to 

 show that there is another large class in the domain 

 of instinct. 



If instinct be, as Professor Hering, Mr. Samuel 

 Butler, and others have argued, "hereditary habit" 

 i. e. if it comprises an element of transmitted ex- 

 perience we at once find a complete explanation of 

 many cases of the display of instinct which otherwise 

 remain inexplicable. For although a large number 

 or even, as I believe, a large majority of instincts 

 are explicable by the theory of natural selection alone, 

 or by supposing that they were gradually developed 

 by the survival of fortuitous variations in the way of 

 advantageous psychological peculiarities, this only 

 applies to comparatively simple instincts, such as that 

 of a protectively coloured animal exhibiting a prefer- 

 ence for the surroundings which it resembles, or even 

 adopting attitudes in imitation of objects which occur 

 in such surroundings. But in all cases where instincts 

 become complex and refined, we seem almost com- 

 pelled to accept Darwin's view that their origin is to 



