no THE EVOLUTION OF MAN 



centives to the solution of simple problems, either by creating 

 strong hunger, or by the use of somewhat severe punishment. 

 In either case, it is alleged that the animal is thrown into an ab- 

 normal emotional condition highly prejudicial to the exercise 

 of such powers of intelligence as it may possess. Objections 

 of this character are all appreciably less significant when urged 

 against the milder and less unnatural forms of experimental 

 procedure employed, let us say, in the case of simple marine 

 animals, to whom can be given, under laboratory conditions, 

 surroundings so closely simulating their native habitat as pre- 

 sumably to rob them of any real abnormality. Moreover, 

 after every criticism has been recorded, it still remains true 

 that, when affirmative evidence of intelligent behavior is 

 secured under conditions of experimental control, whether 

 inside or outside a laboratory, the validity of such evidence is 

 likely to be forever exempt from the uncertainty which almost 

 inevitably attaches to the incidental observations of animals in 

 nature. 



It is necessary to direct attention to these two main lines of 

 attack upon animal intelligence, for the reason that observa- 

 tions which have been reported from these two sources have 

 often varied fundamentally. The works of the outdoor 

 naturalist, for example, are full of records of animal be- 

 havior alleged to afford the most unequivocal evidence of 

 reasoning processes approximating those of man himself, 

 whereas the experimentalists have generally failed to discern 

 anything of this kind and in its place have reported literally 

 thousands of instances of behavior wholly devoid of the char- 

 acteristic features of human thinking. 



It will be readily understood that no observation of animal 

 behavior is likely to be trustworthy, unless based upon a wide 

 and exact knowledge of the animal's usual habits of life. 

 Otherwise one is exposed to the error of interpreting as a 



