Animal Intelligence / The International Scientific Series, Vol. XLIV.

by George John Romanes

Mr. Darwin writes: 'Rengger, a most careful observer, states that when first he gave eggs to his monkeys in Paraguay, they smashed them, and thus lost much of their contents; afterwards they generally hit one end against some hard body, and picked off the bits with their fingers. After cutting themselves only once with any sharp tool, they would not touch it again, or would handle it with the greatest caution. Lumps of sugar were often given them wrapped up in paper; and Rengger sometimes put a live wasp in the paper, so that in hastily unfolding it they got stung; after this had once happened, they always first held the packet to their ears to detect any movement within.'[277]

The powers of observation and readiness to establish new associations thus rendered apparent, display a high level of general intelligence. Mr. Darwin further observes that Mr. Belt 'likewise describes various actions of a tamed cebus, which, I think, clearly show that this animal possessed some reasoning power.' The following is the account to which Mr. Darwin here refers, and I quote it in extenso, because, as I shall presently show, I have myself been able to confirm most of the observations on another monkey of the same genus:—

It would sometimes entangle itself round a pole to which it was fastened, and then unwind the coils again with the greatest discernment. Its chain allowed it to swing down below the verandah, but it could not reach to the ground. Sometimes, when there were broods of young ducks about, it would hold out a piece of bread in one hand, and when it had tempted a duckling within reach, seize it by the other, and kill it with a bite in the breast. There was such an uproar amongst the fowls on these occasions, that we soon knew what was the matter, and would rush out and punish Mickey (as we called him) with a switch; so that he was ultimately cured of his poultry-killing propensities. One day, when whipping him, I held up the dead duckling in front of him, and at each blow of the light switch told him to take hold of it, and at last, much to my surprise, he did so, taking it and holding it tremblingly in one hand. He would draw things towards him with a stick, and even used a swing for the same purpose. It had been put up for the children, and could be reached by Mickey, who now and then indulged himself in a swing on it. One day I had put down some bird-skins on a chair to dry, far beyond, as I thought, Mickey's reach; but, fertile in expedients, he took the swing and launched it towards the chair, and actually managed to knock the skins off in the return of the swing, so as to bring them within his reach. He also procured some jelly that was set out to cool in the same way. Mickey's actions were very human-like. When any one came near to fondle him, he never neglected the opportunity of pocket-picking. He would pull out letters, and quickly take them from their envelopes.[278]

I shall now proceed to state some further facts, showing the high level of intelligence to which monkeys of various kinds attain.

The orang which Cuvier had used to draw a chair from one end to the other of a room, in order to stand upon it so as to reach a latch which it desired to open; and in this we have a display of rationally adaptive action which no dog has equalled, although, as in the case before given of the dog dragging the mat, it has been closely approached. Again, Rengger describes a monkey employing a stick wherewith to prise up the lid of a chest, which was too heavy for the animal to raise otherwise. This use of a lever as a mechanical instrument is an action to which no animal other than a monkey has ever been known to attain; and, as we shall subsequently see, my own observation has fully corroborated that of Rengger in this respect. More remarkable still, as we shall also subsequently see, the monkey to which I allude as having myself observed, succeeded also by methodical investigation, and without any assistance, in discovering for himself the mechanical principle of the screw; and that monkeys well understand how to use stones as hammers is a matter of common observation since Dampier and Wafer first described this action as practised by these animals in the breaking open of oyster-shells. The additional observation of Gernelli Carreri of monkeys thrusting stones into the open valves of oysters so as to save themselves the trouble of smashing the shells, though not incredible, requires confirmation. But Mr. Haden, of Dundee, has communicated to me the following very remarkable appreciation of mechanical principles which he himself observed in a monkey (species not noted), and which would certainly be beyond the mental powers of any other animal:—

'A large monkey, confined alone in a large cage, had its sleeping-place in the form of a kind of hut in the centre of the cage. Springing near the hut was a tree, or imitation tree, the main branch of which ascended over the top of the hut, and then came forwards away from it. Whether the roof of the hut enabled this animal to gain any part of this branch, I did not observe, but only remarked its method at the time of gaining the part of the branch which led frontwards, and away from the hut. This could be done by means of the hut door, which, when opened, swung beneath this part of the branch. The door, either by accident or by the design of its construction, swung to each time the animal opened it to mount upon its top edge. After one or two efforts to mount by it in spite of its immediate swinging to, the creature procured a thick blanket which lay in the cage, and threw it over the door, having opened the same, so that its complete swinging to was prevented sufficiently for the creature to mount upon its free edge, and so gain that part of the branch which ran above it.'

The following, which I quote from 'Nature' (vol. xxiii., p. 533), also displays high intelligence:—

One of the large monkeys at the Alexandra Palace had been for some time suffering from the decay of the right lower canine, and an abscess, forming a large protuberance on the jaw, had resulted. The pain seemed so great, it was decided to consult a dentist as to what should be done; and, as the poor creature was at times very savage, it was thought that if the tooth had to be extracted, gas should be used for the safety of the operation. Preparations were made accordingly, but the behaviour of the monkey was quite a surprise to all who were concerned. He showed great fight on being taken out of the cage, and not only struggled against being put into a sack prepared with a hole cut for his head, but forced one of his hands out, and snapped and screamed, and gave promise of being very troublesome. Directly, however, Mr. Lewen Moseley, who had undertaken the operation, managed to get his hand on the abscess and gave relief, the monkey's demeanour changed entirely. He laid his head down quietly for examination, and, without the use of the gas, submitted to the removal of a stump of a tooth as quietly as possible.