THE MEANING OF EVOLUTION 283 



and effort in the one case, and of lack of conscious effort 

 in the other. 



The difference is one of those which separate 

 instinctive from intelligent activities. Now we hesitate 

 to attempt the discussion of this much-controverted 

 question of the distinction between instinct and intelli- 

 gence : after reading much that has been said as to 

 the nature of this difference, one rises with the uncom- 

 fortable impression that the time is not yet ripe for its 

 discussion, and that the problem is still one far more 

 for the naturalist than for the psychologist. Reliable 

 data are still urgently required. Yet it is a question 

 which we cannot fail to consider. The typical plant 

 differs from the typical animal in that a sensori-motor 

 system has been evolved in the one but not in the 

 other ; and among the animals in which this system 

 is developed to a high degree the activities which involve 

 its exercise differ in their form. Actions of a stereo- 

 typed pattern characterise the behaviour of the higher 

 Invertebrate, while in the higher Vertebrate all that we 

 see indicates that the behaviour is the result of delibera- 

 tion, and that the actions performed are not stereotyped 

 but differ infinitely in their patterns. Just as clearly 

 as differences in morphology differentiate Arthropod 

 from Vertebrate, so also do differences in the mode of 

 activity of the sensori-motor system mark divergent 

 lines of evolution culminating in the Hymenopterous 

 Insect on the one hand and in Man on the other. 



What is the essential difference between an action 

 performed instinctively and one performed intelli- 

 gently ? It is not that the animal is unaware of its 

 activity in the first case and not in the second ; how- 

 ever much we tend to ' ' explain ' ' organic activity in 

 terms of inorganic reactions, we do not really believe 

 that the instinctively acting wasp is a pure automaton, 



