It is difficult to compare the mental status of the ape to that of man, because there is no common basis upon which the two rest. Their modes of life are so unlike as to afford no common unit of measure. Their faculties are developed along different lines. The two have but few problems in common to solve. While the scope of the human mind is vastly wider than that of the ape, it does not follow that it can act in all things with more precision. There are, perhaps, instances in which the mind of the ape excels that of man by reason of its adaptation to certain conditions. It is not a safe and infallible guide to measure all things by the standard of man’s opinion of himself. It is quite true that, by such a unit of measure, the comparison is much in favor of man; but the conclusion is neither just nor adequate. It is a problem of great interest, however, to compare them in this manner, and the result indicates that a fair specimen of adult ape is in about the same mental horizon as a child of one year old. But if the operation were reversed and man were placed under the natural conditions of the ape, the comparison would prove much less in favor of man. There is no common mental unit between them.
On problems that concern his own comfort or safety the chimpanzee exercises the faculty of reason with a fair degree of precision. He is quick to interpret motives or to discern intents, and he is a rare judge of character. He is inquisitive, but not so imitative as monkeys are. He is more observant of the relations of cause and effect. In his actions he is controlled by more definite motives. He is docile and quickly learns anything that lies within the range of his own mental plane.
The opinion has long prevailed that these apes subsist upon a vegetable diet. That is a mistake. In this respect their habits are much the same as those of man, except that the latter has learned to cook, but the former eats his food raw. Their natural tastes are greatly diversified, and they are not all equally fond of the same articles of food. Most of them are partial to the wild mango, which grows in abundance in certain localities in the forest. This is often available when other kinds of food are scarce. It thus becomes, as it were, a staple article of food. There are many kinds of nuts to be found in their domain, but the nut of the oil palm is a great favorite. They sometimes eat the kola nut, but they are not partial to it. Several kinds of small fruits and berries also form part of their diet. They eat the stalks of some plants, the tender buds of others, and the tendrils of certain vines. The names of these vines I do not know.
Most of the fruits and plants that are relished by them are either acidulous or bitter in taste. They are not especially fond of sweet fruits. They prefer those having the flavors mentioned. They eat bananas, pineapples, or other sweet fruits, but rarely do so from choice. Most of them appear to prefer a lime to an orange, a plantain to a banana, a kola nut to a sweet mango. In captivity they acquire a taste for sweet foods of all kinds.
In addition to these articles they devour birds, lizards, and small rodents. They rob birds of their eggs and their young. They make havoc of many kinds of large insects. Those that I have owned were fond of cooked meats and salt fish, either raw or cooked.
CHAPTER XII
The Speech of Chimpanzees—A New System of Phonetic Symbols—Some Common Words—Gestures
The speech of chimpanzees (as of other simians) is limited to a few sounds, and these chiefly relate to their natural wants. The entire vocabulary of their language embraces perhaps not more than twenty-five or thirty words. Many of them are vague or ambiguous, but they express the concept of the ape with as much precision as it is defined to his mind, and quite distinctly enough for his purpose.
During my researches I have learned ten words of the speech of this ape, so that I can understand them and make myself understood by them. In tone, pitch, and modulation most of the sounds are within the compass of the human voice. Two of them are much greater in volume than it is possible for the human lungs to reach, and one of them rises to a pitch more than an octave higher than a human voice of middle pitch. These two sounds are audible at a great distance, but they do not properly fall within the limits of speech.
The vocal organs of the chimpanzee resemble those of man as closely as other physical features have been shown to resemble. They differ slightly in one respect that is worthy of notice. Just above the opening called the glottis (which is the opening between the vocal cords) are two small sacs or ventricles. In the ape these are larger and more flexible than in man. In the act of speaking they are inflated by the air passing out of the lungs into the long tube called the larynx. The function of these ventricles is to control and modify the sound by increasing or decreasing the pressure of the air that is jetted through the tube. They serve at the same time as a reservoir and as a gauge.