It must be admitted that no mammal of any other order, not even the dog, who has associated with us, and been educated, and, strictly speaking, formed by us for thousands of years, acts in the manner described, or exhibits such a high degree of intelligence. And yet a wide gulf lies between the dog-like monkeys and the anthropoid apes, of which I have said that they rise even above the average of monkeyhood.

By the anthropoid apes we understand those which in their structure most resemble man, but are externally distinguished from him by the very prominent canine teeth, the relatively long arms and short legs, the structure of the hand, the ischial callosities present in some species, and the hairy covering of the body. They inhabit the tropical countries of Asia and Africa (the former being richer in species), and they are divided into three families, of which one is confined to Africa. Each of these families embraces only a few species, but probably we do not know nearly all of them as yet.

The structure of the anthropoid apes points to an arboreal life; they are most excellent climbers, though by no means slaves to the tree any more than the langurs, long-tailed monkeys, and macaques. Their movements, however, both among the branches and on the ground, are quite different from those of all other monkeys. In climbing up a tree, particularly a smooth trunk without branches, they take the same position as a man would do, but, thanks to their long arms and short legs, they make much more rapid progress than the most expert human climber; and when they have reached the branches they put every gymnast to shame by the variety and security of their movements. With outstretched arms they seize one branch, with the feet they clasp a parallel one, about half their height lower down, and, using the upper branch as a rail, they walk along the lower one so quickly, though without the least sign of effort, that a man walking underneath must exert himself vigorously to keep pace with them. On reaching the end of the branch, they seize any available bough or twig of the next tree and proceed on their way in the same manner, with undiminished speed, yet without hurry. In ascending they seize hold of any branch strong enough to bear their weight, and swing themselves upwards with equal ease whether they are holding the branch with both hands or only with one; in descending, they let themselves hang with both arms and search about for a new foothold. Sometimes they amuse themselves by swinging freely for some minutes; sometimes, clasping a branch with arms and feet, they walk, for a change, on its lower surface; in short, they assume every imaginable position, and execute every possible movement. Quite unrivalled masters of climbing are the long-armed apes or gibbons, anthropoid apes with arms so disproportionately long that, when outstretched, they measure thrice as much as their upright bodies. With incomparable speed and security they climb up a tree or bamboo-stem, set it, or a suitable branch swinging, and on its rebound spring over spaces of from eight to twelve yards, so lightly and swiftly, that they seem to fly like a shot arrow or an alighting bird. They are also able to alter the direction of a leap while actually springing, or to cut it suddenly short by seizing a branch and clinging to it—swinging, rocking, and finally climbing up by it, either to rest for a little, or to begin the old game anew. Sometimes they spring through the air in this manner three, four, or five times in succession, so that one almost forgets that they are subject to the law of gravity. Their walking is as awkward as their climbing is excellent. Other anthropoid apes are able to traverse a considerable distance in an upright position—that is, on their feet alone, without special difficulty, though when in haste they always fall on all-fours, resting on the inturned knuckles of the fingers and the outer edges of the feet, and throwing the body laboriously and clumsily forward between the extended arms. But the long-armed apes move in an upright position only in cases of extreme necessity, and then they hop rather than walk. When the distance to be covered is a short one they raise themselves to their full height, and preserving their balance by extending their arms, now more, now less, spread out the great toes as far as possible, and patter pitiably along with short, quick steps. Their power of movement must therefore be characterized as one-sided, for their superiority over the other anthropoid apes in climbing does not counterbalance their helplessness on the ground.

The voice-power of the anthropoid apes is very noteworthy. We find that the most active and agile species have the loudest voices, while those of the more widely developed, though less nimble, anthropoid apes are capable of greater variety of expression. I do not say too much when I assert that I have never heard the voice of any mammal—man, of course, always excepted—which was more full-toned and sonorous than that of a long-armed ape which I observed in captivity. I was first astonished, then delighted, with these deep notes, uttered with full strength, and by no means disagreeable, because perfectly clear and well-rounded. In one species the ringing call, which I should describe as a song rather than a cry, begins on the key-note E, ascends and descends in semitones through the chromatic scale for a full octave, sometimes ending with a shrill cry, which seems to be uttered with the animal’s whole strength. The key-note remains audible throughout, and serves as a grace-note to each of the succeeding ones, which, in ascending the scale, follow each other more and more slowly, in descending more and more quickly, at last with extreme rapidity, but always with perfect regularity. The notes of some species of the group are said to be less clear, but all are so loud that, in the open air, one can hear them distinctly at a distance of an English mile. The same correlation between agility of motion and voice-power can be observed in other anthropoid apes. The slow-moving, awkward-looking orang-utan utters, as far as I know, only a strong, deep throat sound; the lively, active, sprightly chimpanzee, with only a few notes, understands so well how to give them variety of emphasis and intelligible expression that one is tempted to concede to him the power of speech. He does not indeed speak with words, but with sounds, and even syllables, of the constancy of whose meaning the observer who has much acquaintance with the chimpanzee can have no doubt. Other anthropoid apes of the same family are probably not far behind him in this respect.

Anyone who wishes to learn to what a height the mental qualities of a monkey may reach must select the chimpanzee or one of his nearest relatives for observation, and must associate closely with it for a lengthened period, as I have done. He will then discover with wonder and amazement, perhaps with slight horror, how much the gulf between man and beast can be diminished. The other anthropoid apes, too, are highly gifted creatures; they, too, surpass all other monkeys in this respect; but the talents of the long-armed gibbons or the orang-utans do not attain to the same universally intelligible expression—I may say, the same impressiveness, as those of the chimpanzees and their relatives. They—the pongos, the gorilla, the tschiego, and the chimpanzee—cannot be treated as animals, but must be associated with as men, if their mental powers are to be known and appreciated. Their intelligence is not far behind that of a rude, undisciplined, uneducated human being. They are, and remain animals, but they behave so humanly that one can almost lose sight of the beast.

For years in succession I have kept chimpanzees, have observed them closely and, as far as possible, without prejudice, have associated intimately with them, taken them into my family, brought them up as playmates for my children, let them eat at my table, taught and trained them, waited upon them in sickness, and not forsaken them in the hour of death. I have therefore a right to believe that I know them as well as anyone, and that I am justified in pronouncing an authoritative opinion. For these reasons I select the chimpanzee, in order to show to what height the mental power of an animal may rise.

The chimpanzee is not only one of the cleverest of all creatures, he is a being capable of deliberation and judgment. Everything he does is done consciously and deliberately. He imitates, but he does so with intelligence and on due consideration; he allows himself to be taught, and learns. He knows himself and his surroundings, and he can appreciate his position. In association with man he yields submission to superior intelligence; in his relations with animals he exhibits a self-conceit similar to our own. What is merely hinted at among other apes is quite pronounced in him. He regards himself as better, as standing higher than other animals, even other monkeys; he rates even human beings exactly according to their standing; thus he treats children quite differently from grown-up people; the latter he respects, the former he looks upon as comrades and equals. He shows an interest in animals with which he can form no friendship or other tie, and also in objects which have no connection with his natural wants; for he is not merely inquisitive, he is greedy of knowledge; an object which has attracted his attention increases in value in his eyes when he has found out its use. He can draw conclusions, can reason from one to another, and apply the results of experience to new circumstances, is cunning, even wily, has flashes of wit, and indulges in practical jokes, exhibits humours and moods, is entertained in one company and bored in another, enters into the spirit of some jokes and scorns others, is self-willed but not stubborn, good-natured but not wanting in independence. He expresses his emotions like a human being. When in a gay mood he smirks with satisfaction, when depressed his face is drawn into wrinkles which speak for themselves, and he gives utterance to his grief by plaintive sounds. In sickness he behaves like one in despair, distorts his face, screams, throws himself on his back, beats with his hands and feet, and tears his hair. To a friendly voice he responds with sounds expressive of pleasure, to chiding with cries of distress. He is active and busy from morning till late in the evening, seeks constant occupation, and when he comes to an end of his usual employments he invents new ones, even if it should only be slapping his feet with his hands, or knocking against hollow boards, and thus producing sounds which give him evident pleasure. In a room he occupies himself with carefully examining everything that attracts his attention, opens drawers and rummages among their contents, opens the stove door to look at the fire and shuts it again, holds a key properly, stands before the mirror and amuses himself with the reflection of his own gestures and grimaces, uses brush and duster as he has been taught, puts on blankets and clothing, and so on.

His acuteness of observation is strikingly proved by his almost unfailingly correct judgment of persons. Not only does he recognize and distinguish his friends from other people, but well-meaning from evil-intentioned persons so thoroughly that the keeper of a chimpanzee was convinced that anyone with whom his protégé refused to make friends was really a good-for-nothing or a scoundrel. A thorough but accomplished hypocrite who deceived me and others was all along a horror to our chimpanzee, just as if he had seen through the red-headed rascal from the first. Every chimpanzee who has been much in human society likes best to be a member of a family circle. There he behaves as though he felt himself among equals. He carefully observes the manners and customs of the house, notices immediately whether he is being watched or not, and does in the former case what he ought to, in the latter what pleases him. In contrast to other monkeys, he learns very easily and with real eagerness whatever is taught to him, as, for instance, to sit upright at table, to eat with knife, fork, and spoon, to drink from a glass or cup, to stir the sugar in his tea, to touch glasses with his neighbour, to use his napkin, and so on; with equal case he becomes accustomed to clothing, beds, and blankets; without great difficulty he gains after a time an understanding of human speech which far surpasses that of a well-trained dog, for he follows not merely the emphasis but the meaning of words, and executes commissions or obeys commands with equal correctness. Exceedingly appreciative of every caress and flattery, and even of praise, he is equally sensitive to unfriendly treatment or blame; he is also capable of deep gratitude, and he expresses it by shaking hands or kissing without being asked to do so. He evinces a special fondness for children. Being neither spiteful nor vicious, he treats children with great friendliness as long as they do not tease him, and behaves to helpless infants with really touching tenderness, though towards others of his own species, monkeys of a different species, and animals generally, he is often rough and harsh. I lay special stress on this characteristic, which I have observed in every chimpanzee I have brought up, because it seems to prove that the chimpanzee recognizes and respects the human even in the youngest child.

The behaviour of a sick and suffering anthropoid ape is most touching. Begging piteously, almost humanly, he looks into his keeper’s face, receives every attempt to help him with warm thanks, and soon looks upon the physician as a benefactor, holds out his arm to him, or stretches out his tongue as soon as he is told, and even does so of his own accord after a few visits from the physician. He swallows medicine readily, submits even to a surgical operation, and, in a word, behaves very like a human patient in similar circumstances. As his end approaches he becomes more gentle, the animal in him is lost sight of, and the nobler traits of his character stand out prominently.

The chimpanzee which I kept longest, and with the help of an intelligent, animal-loving keeper educated most carefully, was taken ill with inflammation of the lungs, accompanied by suppuration of the lymphatic glands of the neck. Surgical treatment of the glands was found necessary. Two surgeons, friends of mine who were on good terms with the chimpanzee, undertook to open the tumour on the neck, the more readily that the monkey believed that to be the cause of his suffering, and continually guided the surgeon’s hand towards it. But how was the necessary operation in such a dangerous spot to be performed without imperilling the monkey’s life? Anæsthetics were out of the question because of the lung disease, and the attempt to have the chimpanzee held down by several strong men had to be abandoned because of his intense excitement, and the strenuous resistance he offered. But where force failed persuasion succeeded. When the monkey was quieted and reassured by the coaxing and endearments of his keeper, he allowed a further examination of the swelling, and even submitted, without twitching an eyelid or uttering a complaint, to the use of the knife, and other painful treatment, including the emptying of the opened tumour. When this was done the distressingly laboured breathing became instantly less oppressive, an unmistakable expression of relief passed over the sufferer’s face, and he gratefully held out his hand to both physicians, and embraced his keeper, without having been asked to do either.

Unfortunately, the removal of the one trouble did not succeed in saving the animal’s life. The neck wound healed, but the inflammation of the lungs increased and killed him. He died fully conscious, gently and peacefully, not as an animal, but as a man dies.

These are features of the character and conduct of anthropoid apes which can neither be misunderstood nor cavilled at. When one considers that they can be observed in all anthropoids not yet full-grown but beyond the stage of childhood, one must undoubtedly grant those animals a very high place. For the opinion expressed by some one incapable observer, and thoughtlessly repeated by hundreds, that the monkey loses mental power with increasing age, that he retrogrades and becomes stupid, is completely false, and is disproved by every ape which is observed carefully, and without prejudice, from youth to age.[73] Even if we knew nothing more about full-grown anthropoids than that they erect shelters resembling huts rather than nests, in which to pass a single night, and that they drum on hollow trees for amusement, it would be enough to lead us to the same conclusion as we have arrived at by observation of the young members of this group; that is, that they must be regarded as by far the most gifted and highly developed of animals, and as our nearest relatives.

And the ape question? I might say that I have just answered it in what I have said; but I have no hesitation in expressing a more definite opinion.

Everyone must admit that man is not the representative of a new order of being, but is simply a member of the animal kingdom, and every unprejudiced person will also describe apes as the creatures most resembling man. If we compare them with one another, and then with man, the conviction is forced upon us, however we may strive against it, that there is a greater difference between the marmosets and the anthropoid apes than between the latter group and man. Zoologically, therefore, one cannot even relegate the apes and man to different orders of the highest class of animals. This has indeed been done, and is still done, man being classed as two-handed and monkeys as four-handed animals, but this leaves the most important aid to the classification of a mammal, the dentition, out of the question. For the dentition of man and monkeys is so essentially similar that it points imperatively to the necessity of placing the two types together. Nor is the distinction between two-handed and four-handed tenable, for although as regards the structure of hands and feet man and monkeys are certainly different, the difference does not imply any opposition; and the monkeys are just as much two-handed as we are. If we keep to the basis of classification adhered to without exception elsewhere, we are forced to place both in one order. I have given to it the name Hochtiere.

But though the characteristics which belong to all the higher animals as members of one order correspond thus accurately, a closer comparison reveals differences between man and apes which absolutely forbid a fusion of the two groups such as has been attempted in modern times. The symmetry of form, the comparative shortness of the arms, the breadth and mobility of the hands, the length and strength of the legs, as well as the flatness of the feet, the naked skin, and the less-developed canine teeth are external marks of man which must not be under-estimated, for they are important enough to justify putting him and the apes in different families, perhaps even different sub-orders. If, in addition, we take man’s endowments into due consideration, compare his movements, his articulate speech, his mental capacities with the corresponding gifts in the ape, the need for insisting on the boundaries between the two is confirmed.

Blind disciples of the Doctrine of Descent, as Darwin founded it and others developed it, do indeed cross these boundaries without hesitation, but they cannot possibly be regarded as giving a carefully thought-out and authoritative judgment on the actual state of the case. Satisfactory, not to say probable, as this doctrine is, it has not yet risen above the level of an ingenious hypothesis; and incontrovertible evidence for the correctness of this hypothesis has not yet been produced. Variation within the limits of species and breed can be proved, can even be brought about; but transformation of one species into another cannot be established in any case. As long as this is so we are justified in regarding man and apes as creatures of different nature, and disputing the descent of one from the other. No attempt to discover or establish a common ancestor, no undertaking to draw up a pedigree for man, alters this in the slightest; for true natural science is not satisfied with interpretative theories, it demands proofs; it does not want to believe, but to know.[74]

So we may without scruple give the apes the place in the scale of being which unprejudiced investigation points out. We may look upon them as the animals most resembling ourselves, and as our nearest relatives in the zoological sense; anything more than this we must deny. Much that is characteristic of man is to be found in the apes also; but a wide gulf still remains between them and true humanity. Physically and mentally they have many of the characteristics of man, but by no means all.