xvi Introduction. 



licence all alone the line of animal evolution. It tends only to confusion, however, to 



o o 



call those acts of association which lead to acquired habits, instincts, or the countless 

 mechanical or chemical reactions of organisms to external stimuli, the expressions of 

 intelligence and thought. " Go to the ant thou sluggard ! " is good advice, but one should 

 bring from the ant a trustworthy account of how it performs its wonderful works. It is im- 

 portant to distinguish the root from the bud, as well as from the perfected flower and fruit. 



Although this is not a treatise on animal behavior, a general working theory has been 

 adopted and will now be given. Every animal at birth inherits with its bodily organs the 

 power to use them in a more or less definite way, and all but the lowest animals, of which 

 the Protozoa, jelly-fishes, and possibly the worms may be taken as representatives, acquire 

 some power of learning to do things in the course of their lives. Their equipment thus 

 consists of (i) unlearned or inherited powers, and (2) of learned or acquired abilities, which 

 are the results of experience often very bitter. The term " instinct " when used in a very 

 broad sense may be given to all inherited or ingrained tendencies, and " habit " reserved 

 for what is acquired or learned through a process of association of certain things with 

 certain acts. An animal's powers thus consist of free gifts at its start in life, and later 

 acquisitions gained through its own efforts in the struggle for existence. 



The catalogue of instinctive acts even in the narrower sense of involving a number 

 of different organs is surprisingly great in an animal standing so high in the scale as the 

 bird, but examples drawn from a single species will suffice. When the spring comes the 

 young bird, who returns to the place of its birth, is prompted to find a mate, and with her 

 soon begins to build a nest. Though unattended by instructors and unprepared by prac- 

 tice, it uses the inherited tools of its guild bill, breast, and feet with a nice precision, 

 and be it Oriole, Robin, Flycatcher, or Vireo, follows with wonderful closeness the type of 

 architecture which its ancestors have used for ages. 



Why does the Robin in its first attempt at nest-building begin by laying a foundation 

 of dry grass or stubble, and add to this mud softened with water and made into a mortar, 

 which it then heaps about its breast and molds into a symmetrical cup, often selecting a 

 rainy day for the work? One might as well ask why the Robin lays blue eggs, or why it 

 utters its well known call. It acts in these ways because it must, because Robins have 

 been doing these things for hundreds of generations. It not only inherits tools, but a cer- 

 tain aptitude for their use. Its organization compels or determines its actions. 



No learning of such initial actions is required or even possible since all this has been 

 attended to, as one might say, centuries before the animal was born. These instinctive 

 responses are spontaneous, and when the right button is pressed or the right stimulus ap- 

 plied from without or within, the reaction follows as a matter of course. Of course the 

 Robin must make a mortar of mud and straw; of course it must lay blue eggs, and after 

 incubating them, carefully rear and feed its young. To do otherwise would not only be 

 absurd, but very uncomfortable. Had its ancestors been Cowbirds it would have made 

 no nest at all, but filched another's, and foisting its eggs upon some simple minded nurse, 

 shirked the duties of parents to their offspring. The Cowbird was thus very early to enter 

 the field of experimental psychology. 



Every bird must follow the laws of its nature, and its inherited instincts are no more 

 wonderful than its inherited organs, its vocal cords, its keen eyes, and its marvelous 

 feathers. 



