1 82 Animal Life and Intelligence. 



forget that many questions remain behind, all centering 

 round that little question, to which an adequate answer is 

 so difficult to give, the question How ? Eeduced to its 

 simplest expression, the doctrine of evolution merely states 

 that the animal world as it exists to-day is naturally 

 developed out of the animal world as it existed yesterday, 

 and will in turn develop into the animal world as it shall 

 exist to-morrow. This is the central belief of the evolu- 

 tionist. No matter what moment in the past history of 

 life you select, the life at that moment was in the act of 

 insensibly passing from the previous towards a future con- 

 dition. Then at once arises the question Does life remain 

 the same yesterday, to-day, and to-morrow ? A thousand 

 indubitable facts at once make answer No ! Underlying 

 the law of continuity there is a law of change. Life to-day 

 is not what it was yesterday, nor will it be to-morrow the 

 same as to-day. What, then, is the nature of this change ? 

 If it be replied that the change must be either for the 

 better or the worse, we shall have to answer the further 

 question Better or worse in what respects ? 



Let us narrow our view from the contemplation of life 

 as a whole to the more particular consideration of an 

 organism as one of its constituent units. The individual 

 life of that organism depends on (some would say consists 

 in) its ceaseless adaptation to surrounding circumstances. 

 The circumstances remaining the same, or only varying 

 within constant limits, the adaptation may be more or less 

 perfect. A change in the direction of more perfect adapta- 

 tion will be a change for the better, a tendency to less 

 perfect adaptation will be a change for the worse. 



But the relation of an organism to its circumstances or 

 environment is itself subject to change. The environment 

 itself may alter, or the organism may be brought into relation 

 with a new environment. We have to consider not only 

 the changes in an organism in the direction of more or 

 less perfect adaptation to its environment, but also changes 

 in the environment. These changes are in the direction 

 of increased simplicity or of increased complexity. So 



