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This eBook from the Gutenberg Project consists of approximately 205 pages of information about The Mental Life of Monkeys and Apes.
absence of anything more interesting, even a staple or a small nail might receive his undivided attention for minutes at a time.  How important is the species difference in this connection, I have no means to judge, but if we may not consider these different modes of behavior characteristic of P. rhesus as contrasted with P. irus, we must conclude that remarkable individual differences exist among monkeys, for whereas Skirrl is by nature a mechanical genius, Sobke has apparently no such disposition.  I can imagine no more fascinating task than the careful analytical study of the temperaments of these two animals.  Skirrl’s behavior has importantly modified my conception of genius.

V

MISCELLANEOUS OBSERVATIONS

1. Right- and left-handedness

Several years ago Doctor Hamilton reported to me observations which he had made on preference for the right or left paw in dogs.  He has not, I believe, published an account of his work.  Subsequently, Franz observed a similar preference in monkeys which, according to his report, exhibit marked tendency to be right-handed, left-handed, or ambidextrous.

My own observations, although they are wholly incidental to my other work, seem worthy of description at this point.  I noted, first of all, that the orang utan Julius tended to use his left hand.  He by no means limited himself to this, but in difficult situations he almost invariably reached for food or manipulated objects in connection with food getting with the left hand.  Figures 23 and 24 of plate V, show him reaching for a banana with the left hand.  Likewise, figure 34 exhibits the use of the left hand in the draw-in experiment.

So marked was Julius’s preference for his left hand that I became interested in observing similar phenomena in the monkeys.  Skirrl, when driving nails, held the hammer with his left hand and the nail with his right hand.  The fact that he never was observed to reverse the use of the hands is surprising, for other observations indicate that he preferred the right hand for certain acts.

Stimulated by the obvious left-handedness, in certain connections, of Julius and Skirrl, I tested the preference of several of the monkeys in the following simple way.  Standing outside the cage I would hold out a peanut to a hungry animal, keeping it so far from the cage that the monkey could barely reach it with its fingers.  I noted the hand which was used to grasp the food.  Next I varied the procedure by placing the peanut on a board in order to make sure that I was not definitely directing the animal’s attention.

With Sobke the following results were obtained.  In forty trials given on two different days, he reached for and obtained the food each time with his left hand.  Only by holding the bait well toward the right side of his body was it possible to induce him to use the right hand.  So far as may be judged from these observations and from others in connection with the experiments, this animal is definitely left-handed.

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