It is quite impossible to represent the sounds of monkey speech by any literal formula, and it is difficult to translate them into their exact equivalent of human speech; but, in order to convey some idea of the nature and scope of that speech, I shall describe a word or two. In the tongue of the brown Capuchin monkey the most important word somewhat resembles the word “who,” uttered like “wh-oo-w.” The phonetic effect is rich and musical. The vowel element which dominates it is a pure vocal “u.” The radical meaning of this sound is food, which is the central thought of every monkey’s life. It does not only mean food in the concrete sense, referring to the thing to be eaten, but it sometimes refers to the act of eating, in which sense it has the character of a verb. At other times it refers to the desire to eat or to the sensation of hunger, in which instance it may be said to have the character of an adjective. But grammatical values depend upon structure, and since the speech of monkeys is monophrastic it cannot truly be said to have grammatical form. All the sounds of this species, so far as I have seen, are monosyllables; and most of them contain but one distinct phonetic. I have therefore described them as “monophonetic.” The word above described is sometimes used with the apparent purpose of expressing friendship, or something of that kind.
Another word which refers to drink, or liquid, begins with a faint guttural “ch,” gliding through a sound resembling the French diphthong “eu,” and ending with a vanishing “y.” The sound is used with reference to drink in much the same way as the other sound is used with reference to food.
So far I have not found any trace of the vowels “a,” “e,” “i,” or “o,” sounded long, but in one sound of alarm emitted under stress of great fear or in case of assault, the vowel element resembles short “i.” This sound is uttered in a pitch about two octaves above a human female voice.
All of the sounds made by monkeys and, so far as I have observed, by other animals, refer to their natural physical wants. They are not capable of expressing intricate or abstract thoughts, for the animal himself has no such thoughts. Their simple modes of life do not require complex thoughts.
A striking point of resemblance between human speech and that of the simian is found in a word that “Nellie” (one of my pets) used in warning me of the approach of danger. It is not that sound elsewhere described as the alarm sound used in case of imminent danger. This sound is used in case of remote danger or in announcing something unusual. As nearly as can be represented by letters it resembles “e-c-g-k.” With this word I have often been warned by these little friends. Nellie’s cage occupied a place near my desk. At night she would always stay awake as long as the light was kept burning. Having always kept late hours myself, I did not violate the rule of my life in order to give her a good night’s rest. About two o’clock one morning, when about to retire, I found Nellie wide awake. I drew a chair near her cage and sat watching her pranks. She tried to entertain me with bells and toys. Without letting her see it, I tied a long thread to a glove and placed it in the corner of the room at a distance of several feet away. Holding one end of the string, I drew the glove obliquely across the floor. When I first tightened the string, which was drawn across one knee and under the other, the glove slightly moved. This her quick eye caught at the first motion. Standing almost on tiptoe, her mouth half open, she cautiously peeped at the glove. Then in a low undertone, verging on a whisper, she uttered the sound “e-c-g-k!” Every second or so she repeated it, at the same time watching to see whether or not I was aware of the approach of this goblin. Her actions were very human-like. Her movements were as stealthy as those of a cat. As the glove came closer and closer she became more and more demonstrative. When at last she saw the monster climbing the leg of my trousers she uttered the sound in a loud voice and very rapidly. She tried to get to the object. She evidently thought it was a living thing. She detected the thread with which the glove was drawn across the floor, but she seemed in doubt as to what part it played in the matter. Her eyes several times followed the thread from my knee to the glove, but I do not think she discovered what caused the glove to move. Having repeated this a few times, with about the same result each time, I relieved her anxiety by allowing her to examine the glove. She did this with marked interest for a moment and then turned away. I tried the same thing again, but failed to elicit from her the slightest interest after she had once examined the glove.
When Nellie first discovered the glove moving on the floor, she attempted to call my attention in a low tone. As the object approached she became more earnest and uttered the sound somewhat more loudly. When she discovered the monster—as she regarded it—climbing up my leg, she uttered the warning in a voice sufficiently loud for the distance over which the warning was conveyed. These facts indicate that her perception of sound was well defined. Her purpose was to warn me of the approaching danger without alarming the object against which the warning was intended. As the danger increased, the warning became more urgent. When she saw the danger at hand, she no longer concealed or restrained her alarm.
Nellie was an affectionate little creature. She hated to be left alone, even when supplied with toys and a super-abundance of food. When she saw me put on my overcoat or take my hat, she foresaw that she would be left alone. Then she began to plead and beg and chatter. I often watched her through a small hole in the door. When quite alone, in perfect silence she played with her toys. Sometimes for hours together she did not utter a word. She was not an exception to the rule that monkeys do not talk when alone.
Although their speech is inferior to human speech, yet in it there is an eloquence that soothes and a meaning that appeals to the human heart.
Briefly stated, the speech of monkeys and human speech resemble each other in all essential points. The speech sounds of monkeys are voluntary, deliberate, and articulate. They are addressed to others with the evident purpose of being understood. The speaker shows that he is conscious of the meaning which he desires to convey through the medium of speech. He awaits and expects a reply. If it is not given, the sound is repeated. The speaker usually looks at the one addressed. Monkeys do not habitually utter these sounds when alone. They understand the sounds made by others of their own kind. They understand the sounds when imitated by a human being, by a phonograph, or by other mechanical means. They understand the sounds without the aid of signs or gestures. They interpret the same sound in the same way at all times. Their sounds are made by their vocal organs and are modulated by the teeth, the tongue, the palate, and the lips. Their speech is shaded into dialects, and the higher forms of animals have higher types of speech than the lower ones. The higher types are slightly more complex and somewhat more exact in meaning than the lower ones. The present state of monkey speech appears to have been reached by development from lower forms. Each race or species of monkey has a form of speech peculiar to its kind. When caged together for a time they learn the meaning of each other’s sounds, but seldom try to utter them. Their faculty of speech is commensurate with their mental and social status. They utter their speech sounds loud or soft as the condition requires, which indicates that they are conscious of the values. The more pronounced the gregarious habits of any species, the higher the type of speech it has. So far as I am able to discern, there is no intrinsic difference between the speech of monkeys and the speech of men.