3 z8 



THE QUARTERLY REVIEW OF BIOLOGY 



Hearing appears to be about as acute as 

 in man. Taste and smell are utilized very 

 much as by ourselves, primarily with 

 reference to food. All in all, the sensory 

 equipment is definitely analogous to that 

 of man, and different from that of sub- 

 primate mammals. 



This is expectable. A body like ours 

 with senses like those of a dog is a com- 

 bination hardly to be anticipated in 

 nature. The chimpanzee's use of his 

 senses is also human. If he sees some- 

 thing out of his reach but with a string 

 attached to it, he pulls the string with as 

 little hesitation as a human being. If 

 there are several strings, he draws the one 

 lying in most direct line toward himself; 

 or if only one is actually in visual contact 

 with the desired object, he pulls that one. 

 After all, he possesses a string-pulling 

 mechanism — arms and hands and fingers; 

 and this would serve him in little stead if 

 he saw blurred instead of clearly, or if his 

 ability to interpret spatially were de- 

 ficient. 



If food is put on the ground outside a 

 barred window, a string attached to it 

 and led indoors, and an ape allowed to 

 survey the situation, he quickly hauls 

 the food up on the cord. A dog fails to 

 grasp the situation. He may starve 

 before he takes the cord in his mouth 

 and backs across the room to haul the food 

 in. He does not see the relation of food, 

 string, and himself; he cannot connect or 

 synthesize them. 



Tests in which an animal is put under 

 conditions where it makes a selection 

 between several possible acts but is com- 

 pelled to defer action on the choice, have 

 yielded in the rat a memory span of a 

 few seconds; in the dog, a few minutes; 

 in the ape, according to Kohts, a quarter 

 of an hour, and, according to statements 

 of Yerkes, under favorable conditions 

 several hours. In the human being the 



range varies from a few minutes in a small 

 child to years or the entire life in adults. 

 But such deferred choices have something 

 artificial about them. Rats do not en- 

 counter swinging doors and electric flash- 

 lights in nature. The memory span of 

 mammals may be indefinitely long for 

 places, persons, and experiences. What 

 the experiments seem essentially to show 

 is that sub-human animals all make poor 

 showings in tests, the dog slightly sur- 

 passing the rat, and the chimpanzee the 

 dog. Laboratory tests are after all de- 

 vised in culture primarily for organisms 

 that have culture. We may simplify 

 them and yet make them extremely diffi- 

 cult for an organism constructed differ- 

 ently from ourselves. They tend to be 

 weighted humanly, whether we want it 

 or not. 



As regards imitativeness, observations 

 are at variance. Koehler interprets the 

 chimpanzee as much less imitative than 

 does Yerkes. But the latter found a 

 gorilla non-imitative almost to the point 

 of being negatively suggestible. This, 

 however, was with reference to use of 

 appliances or solution of problems such 

 as the animal would not encounter in 

 nature. When it came to eating new 

 foods, the gorilla was willing to follow 

 example — provided no persuasion was 

 applied and it could withdraw to make 

 the test in seclusion. Emotional factors 

 are evidently of the greatest influence as 

 regards imitativeness; and these are con- 

 ditioned by the social relations in which 

 the ape finds itself. Yerkes' orang and 

 chimpanzees were almost members of his 

 household. Koehler's apes lived pri- 

 marily in a colony of their own. It is 

 clear that they learned very little from 

 one another in the solution of posed 

 problems. Imitativeness is evidently 

 called out largely by association with 

 human culture. 



