68 BRAIN MECHANISMS AND LEARNING 



courting. In short, those movements arc inherited: they mature as part of 

 normal development in each individual of the same species in an 

 almost identical way. While this paper was under press I continued my 

 investigation of the ontogeny of behaviour patterns in mammals. These 

 will be described in detail in a later publication, but I should like to 

 mention here one more example illustrating very well a behaviour 

 pattern in a mammal which is extremely little influenced by learning. 

 As is well known, squirrels {Sciuriis vtt\(^aris L.) hide nuts in holes which 

 they dig in the ground. They deposit the nut, stamp it into the ground by 

 repeated blows with the front of the upper incisors and afterwards cover 

 the hole with earth by means of the forepaws. Squirrels raised in grill 

 cages with powder food, by a procedure similar to that described in 

 connection with the rat experiment, were given open nuts. After they had 

 eaten some nuts these animals immediately began to search for a hiding 

 place. With the nut between their teeth they moved over the ground, 

 and wherever the nut met an obstacle they started to scratch as if digging 

 a hole. In many instances they deposited the nut, banged it down with 

 their teeth and finally made covering movements with the forepaws, as if 

 covering the nut with earth, although in fact there was no earth. Only 

 rarely is such a comparatively long chain of reactions innate in mammals. 

 This behaviour of the squirrels was filmed and a detailed analysis will be 

 presented in the near future. 



Some drawbacks of the deprivation experiments have, nevertheless, to 

 be considered. First of all, we must always keep in mind that an animal 

 raised artificially may not show its normal behaviour. How easily an 

 animal is disturbed under the conditions of captivity, is well known to 

 every animal keeper. If certain behaviour patterns characteristic for the 

 species under observation, do not appear in the deprivation experiment, 

 this might be a result of disturbance and not of lack of information. Strictly 

 speaking, the deprivation experiment is conclusive only in case of a 

 positive result. If a specific behaviour pattern comes out despite the 

 specific deprivation situation, we can say that it is a fixed pattern. But if it 

 does not appear, it does not necessarily indicate that the animal needs to 

 learn it. If we keep the animal in good health we may be able to avoid 

 such disturbances. That a certain behaviour pattern does not appear in the 

 experimental situation might, furthermore, be due to lack of the stimuli 

 normally releasing it. To avoid this error a normally raised control animal 

 must be tested under the same conditions as the experimental animal and 

 the experimental animal must be confronted with the situation in which 

 the behaviour pattern normally appears. 



