Curiosity is more strongly pronounced in monkeys than in any other animals. We all know the interesting illustration on this head furnished by the experiment of Mr. Darwin, who, in order to test the statement of Brehm that monkeys have an instinctive dread of snakes, and yet cannot 'desist from occasionally satiating their curiosity in a most human fashion, by lifting up the lid of the box in which the snakes were kept,' took a stuffed snake to the monkey-house at the Zoological Gardens. Mr. Darwin says:—
The excitement thus caused was one of the most curious spectacles I ever beheld. . . . . I then placed a live snake in a paper bag, with the mouth loosely closed, in one of the larger compartments. One of the monkeys immediately approached, cautiously opened the bag, peeped in, and instantly dashed away. Then I witnessed what Brehm has described, for monkey after monkey, with head raised high and turned on one side, could not resist taking a momentary peep into the upright bag, at the dreadful object lying quietly at the bottom.[274]
Allied, perhaps, to curiosity, and so connected with the emotions, is what Mr. Darwin calls 'the principle of imitation.' It is proverbial that monkeys carry this principle to ludicrous lengths, and they are the only animals which imitate for the mere sake of imitating, as has been observed by Desor, though an exception ought to be made in favour of talking birds. The psychology of imitation is difficult of analysis, but it is remarkable as well as suggestive that it should be confined in its manifestations to monkeys and certain birds among animals, and to the lower mental levels among men. As Mr. Darwin says:—
The principle of imitation is strong in man, and especially, as I have myself observed, with savages. In certain morbid states of the brain, this tendency is exaggerated to an extraordinary degree; some hemiplegic patients and others, at the commencement of inflammatory softening of the brain, unconsciously imitate every word that is uttered, whether in their own or in a foreign language, and every gesture or action which is performed near them.
The same sort of tendency is often observable in young children, so that it seems to be frequently distinctive of a certain stage or grade of mental evolution, and particularly in the branch Primates. Other animals, however, certainly imitate each other's actions to a certain extent, as I shall have occasion fully to notice in my next work.
As for the sterner emotions, rage may be so pronounced as to make a monkey exhaust itself with beating about its cage, or a baboon bite its own limbs till the blood flows.[275] Jealousy occurs in a correspondingly high degree, while retaliation and revenge are shown by all the higher monkeys when injury has been done to them, as any one may find by offering an insult to a baboon. The following is a good case of this, as it shows what may be called brooding resentment deliberately preparing a satisfactory revenge. Mr. Darwin writes:—
Sir Andrew Smith, a zoologist whose scrupulous accuracy was known to many persons, told me the following story of which he was himself an eye-witness. At the Cape of Good Hope, an officer had often plagued a certain baboon, and the animal, seeing him approaching one Sunday for parade, poured water into a hole and hastily made some thick mud, which he skilfully dashed over the officer as he passed by, to the amusement of many bystanders. For long afterwards the baboon rejoiced and triumphed whenever he saw his victim.[276]
General Intelligence.
Coming now to the higher powers, I shall give a few cases to show that monkeys certainly surpass all other animals in the scope of their rational faculty. Professor Croora Robertson writes me:—
I witnessed the following incident in the Jardin des Plantes, now many years ago; but it struck me greatly at the time, and I have narrated it repeatedly in the interval. A large ape—I believe anthropoid, but cannot tell the species—was in the great iron cage with a number of smaller monkeys, and was lording it over them with many wild gambols, to the amusement of a crowd of spectators. Many things—fruits and the like—had been thrown between the bars into the cage, which the ape was always forward to seize. At last some one threw in a small hand looking-glass, with a strongly made frame of wood. This the ape at once laid hold of, and began to brandish like a hammer. Suddenly he was arrested by the reflection of himself in the glass, and looked puzzled for a moment; then he darted his head behind the glass to find the other of his kind that he evidently supposed to be there. Astonished to find nothing, he apparently bethought himself that he had not been quick enough with his movement. He now proceeded to raise and draw the glass nearer to him with great caution, and then with a swifter dart looked behind. Again finding nothing, he repeated the attempt once more. He now passed from astonishment to anger, and began to beat with the frame violently on the floor of the cage. Soon the glass was shattered, and pieces fell out. Continuing to beat, he was in the course of one blow again arrested by his image in the piece of glass still remaining in the frame. Then, as it seemed, he determined to make one trial more. More circumspectly than ever the whole first part of the process was gone through with; more violently than ever the final dart made. His fury over this last failure knew no bounds. He crunched the frame and glass together with his teeth, he beat on the floor, he crunched again, till nothing but splinters was left.