BEHAVIOR 163 



complicated activities which are described as instincts to 

 distinguish them from acts of volition. The complexity, 

 orderliness, and utility of these instinctive actions are 

 often astounding, and to one who has not looked into 

 them it might seem that they cannot indicate anything 

 less than the exercise of a very high degree of intelligence. 

 As a matter of fact, careful study demonstrates conclu- 

 sively that these so-called instinctive actions, no matter 

 how complicated and orderly, are purely reflex in origin 

 and control. The animals which carry them out do so 

 on the basis of immediate sensory stimulation, the action 

 follows immediately upon and is determined by the sum 

 total of the sensory stimuli which the animal experiences. 

 It must be admitted that many facts about instinct are 

 not at all understood at present. For example, we may 

 take the instinct of migration in birds. It is clear that 

 the stimulus for migration is an immediate stimulus, 

 based in part probably on chemical changes that go on 

 in the body of the bird itself and in part on features of 

 the environment. But the actual execution of the migra- 

 tion, particularly such feats as the flight of birds from 

 Alaska to a tiny outlying island of the Hawaiian group, 

 and there hitting upon the island with unerring accuracy 

 at the end of hundreds of miles of flight with no single 

 landmark in view, is entirely unexplainable at the present 

 time. 



Behavior Determined by Nervous Organization. — 

 The question of whether in any given species of animal 

 associated memory (volition) shall dominate over pure 

 reflexes (instinct), or whether the reverse shall be the 

 case, is determined by the make-up of the nervous system 

 from birth. Certain kinds of animals inherit from their 

 ancestors a nervous organization in which associated 

 memory plays an important part; others inherit a nervous 

 system in which complicated reflexes determine their be- 

 havior. Human beings belong in the first of these cate- 

 gories, insects in the second. Many forms, particularly 



