MODIFIABILITY OF THE PREFERENTIAL USE OF 

 THE HANDS IN THE RHESUS MONKEY 



K. S. LASHLEY 



Government Hospital for (he Insane 



Observations on handedness in monkeys and apes has not, 

 in general, given evidence for the predominant use of either 

 hand which might be ascribed to heredity and in this respect 

 has not provided phylogenetic support for the view that handed- 

 ness in man is instinctive. Pfungst ('12) reported that in obser- 

 vations on over sixty individuals of different genera the instances 

 of predominant use of either hand could almost always be traced 

 to training or to previous trauma. He has not, however, reported 

 the details of his work. Franz ('13) found that of six monkeys 

 (Macacus rhesus) two were ambidextrous, three used the left 

 hand more frequently than the right, and one was probably 

 right-handed, but doubtful because of the small number of 

 observations which could be made. Lashley and Watson ('13), 

 studying a very young monkey, were unable to demonstrate the 

 predominant use of either hand. Yerkes ('16) made tests upon 

 seven apes, four of which were found to be predominantly left- 

 handed, one right-handed, and two probably ambidextrous. 



Except in the work of Franz not enough observations of any 

 one animal have been reported to demonstrate such a persistent 

 predominant use of one hand in a variety of activities as is neces- 

 sary for a comparison of the condition in the animal with handed- 

 ness in man. During the past summer Dr. Franz placed two 

 young male rhesus monkeys at my disposal, suggesting a con- 

 tinuation of the work upon the preferential use of the hands 

 with a view to the permanent modification of the normal con- 

 dition by training. 1 



Observations were made first upon the preferential use of the 

 hands in a number of different situations to test the effects of 



1 These animals were purchased with a fund granted by the Carnegie Institution 

 of Washington to which acknowledgment is here made. 



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