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Edward John Kempf (1885-1971) was an American psychiatrist and psychobiologist and sometime Vice President of the New York Academy of Sciences who was known especially for his theory that the human personality is a product of biological evolution, and wrote “The Social and Sexual Behaviour of Infrahuman Primates with Some Comparable Facts in Human Behaviour”, published in The Psychoanalytic Review. A Journal Devoted to an Understanding of Human Conduct, volume IV, no. 2, April 1917 (Washington, D. C.) pp. 127-154, one of the earliest studies to draw attention to the common practice of pederasty by monkeys.

Presented here is the approximate half of that essay that is concerned with the pederastic behaviour he observed over eight months in six rhesus macaque monkeys he kept in cages for the purpose, and the insights he gained from it into human behaviour. Macaques (Macaca mulatta) were chosen as a species of Old World Monkey (Cercopithecidae) relatively closely related to humans and “an ideal subject for observation in that it is very easy to generate in him an affective reaction …  and watch its influence on his behavior.”

All the images, except the first one of Dr. Kempf, are of Rhesus macaques.


The Social and Sexual Behaviour of Infrahuman Primates with Some Comparable Facts in Human Behaviour


Edward John Kempf, M. D., in 1928

The careful analyses of a large number of psychotics, including individuals of both sexes, of every educational level and of many nationalities, have consistently shown that the most important etio­logical determinants of psychogenic psychoses, considered in a broad sense, are invariably sexual. Of such cases received at St. Eliza­beth's Hospital, a large proportion of men and women show a striking similarity in their biological constitution, and their psychoses show a definite conformity in certain psychopathological principles. Particularly is this true of many young men received from the army and navy. The cases referred to are at present classified as dementia praecox types, to which group, as deteriorating personalities, they characteristically belong.

The psychopathological mechanisms involved in these cases and their relation to the psychoses will be discussed in another paper. The two important principles that seem to underlie each case are (i) that the individual is the host of well-developed motives, gen­erated at the phylogenetic level, to perform certain sexual acts which he is unable to dissociate or in many instances to even control with­out (2) intensively developing another series of motives (at the habit level) which seem to functionate at the levels of the personality of which he is conscious. They are organized unconsciously for the purpose of controlling or at least diverting the undesirable, otherwise unmodifiable sexual tendencies.

These sexual motives or cravings are in every instance undesirable either (1) because they are biologically unproductive in type and require what are severely, socially censured forms of stimulation of socially censured areas of receptors, or (2) because the affective needs are fixed upon some forbidden or unresponsive object.

Freud, in his Three Contributions to the Theory of Sex, formulated the processes of evolution of the sexual tendencies in the child and their fixation in the adult. This work gives a most acceptable foundation for further investigations into the causes of abnormal sexual tendencies. Naturally attention should also be directed to the phylogenetic determinants, as found in infrahuman primates, for such sexual phenomena as are invariably found in the genus Homo.

Hamilton,[1] influenced by his clinical experience and Freud's contributions, studied the sexual tendencies in monkeys and baboons under environmental conditions which were practically normal for these animals. My observations thoroughly corroborate his although made under unnatural environmental conditions, namely in cages. The generally misunderstood functions of erotogenesis and other affect geneses must be given consideration before psychiatrists establish conclusions about unknown, easily phrased, hereditary and constitutional deficiencies in an individual, as the cause of his psychosis.

Engraving of a sub-species Macac mulatta lasiotis, 1868

We can no longer hold that the individual is solely responsible for his tendencies to homosexuality, autoeroticism or perverseness in his sexual life. His progenitors developed, perhaps needed such interests and we must bring about an enlightened course of sublimation of the abnormal sexual tendencies which often cause so much suffering. It is no more possible to wipe out a well-concatenated system of reflexes of such potency as the erotogenic by an ideal or moral criticism than for a Christian Science healer to evaporate the appendix with local applications of faith and new thought.

In order to obtain more insight into the phylogenetic determinants of man’s social and sexual life and some knowledge of the infrahuman primates’ social and sexual life, six macacus rhesus monkeys were observed for a period of eight months. The macaque is an ideal subject for observation in that it is very easy to generate in him an affective reaction (used in the sense of a desire) and watch its influence on his behavior. His wishes in some instances are slightly but transparently disguised. In him we find man's phylogenetic determinants completely exposed.


[For all that follows, the reader’s attention is drawn to the critical second sentence, where Kempf explains that, putting it here in human terms, A and B were boys, C a girl, and D, E and F men. Without appreciating this, the pederastic character of his findings will be lost.]

The personalities of the six monkeys were as distinctly different as so many people and are described here in detail so that their social and sexual adjustment to one another will be more intelligible.

For convenience the monkeys were named A, B, C, D, E and F. A, B and C were about six months old when acquired. C was a female. D, E and F were males who had reached sexual maturity and were capable of the complete sexual act.

A was very timid and shy. He gave way to the demands of all the others and adapted himself as best he could by any other means than that of using force. Despite the oppressions of the others and his timidity, he was a happy, fastidious little monkey. He would often chuckle with delight when he procured his food, even though it fatally revealed his success to his companions. He usually inspected his food and wiped it with his hands before eating it. When attacked by the other monkeys he invariably took refuge in flight. He was always on the alert to avoid injury by any of them and constantly watched their features, probably the most reliable indicator of the emotional attitude of the other monkeys, to detect the presence of hostile motives in any of them. When they were all congenial he would permit their physical contact and liked to lie on his back even with his abdomen and throat exposed to be picked over for fleas. Sometimes he showed his teeth when cornered and often squealed in anger when scratched, but he rarely fought back and when he did its occurrence was only observed in the manner of a scratch or two at B followed invariably by flight. […] A was always more fond of B than he was of any of the others. […]

B was about the size and age of A but very different in his reaction tendencies or disposition. Where A was timid, B was courageous and aggressive. He dominated A and C, taking food from them at will, and at times even competed with D and E. The larger monkeys punished him occasionally when he became too bold. B was very fond of A and sometimes allowed him to take a piece of extra food which he had laid beside him for future eating. C was never allowed this privilege during the observations. […]

A, B and C were more fond of each other than of the large monkeys, probably because of fear of punishment by them.

D was apparently a matured male. He was usually slower to learn and slower to move than any of the others. When food was placed in the cage or held to the wire, if D did not punish the other monkeys first, he rarely got his share. Neither did he often succeed in taking food from the others. He dominated all of the group except E. E alone consistently tried to take food from him. […]

E was the largest and strongest monkey of the six and recognized as leader of the band. His wishes were never disputed. He was very kindly disposed toward the other monkeys and rarely punished any of them except F. E forced any of the others to submit as his sexual object when it was his pleasure. […]

E was apparently more intelligent than the others, because he often resorted to ruses in order to snatch food from them, […]

F, a quick, alert monkey, was very different in many of his reaction tendencies from any of the other monkeys and was not liked by any of them. They all had other favorites. He was much more cruel than the rest and delighted in punishing the three young ones. He was afraid of E and D, and usually held himself aloof from them unless they made friendly advances to him. He was quicker and seemed to learn more rapidly than D and E. Because D and E were stronger he always packed his cheek pouches before eating so as to be sure of getting sufficient food. He rarely failed to get more than his share. F was dominated by E and D at the food box and he dominated A, B and C at the food box. He often tried to force the latter to submit as sexual objects but he never was observed to try to force D or E to become his sexual objects. On the contrary he submitted for either D or E as the sexual object until either had gratified his sexual hunger. […]

Cambridge Natural History: Mammalia (1902). Figure 268

The individual's method of expressing his desire that the other monkey should assume the sexual position was shown by a characteristic smacking of the lips, pulling upward on the hind quarters of the sexual object, touching, looking at and often smelling of the genitalia and anus of the object. If the affective-motive (desire) was slight this was all that happened. If the exposure of the visual, olfactory and tactile receptors generated more sexual affect it was manifested in the more vigorous play of the aggressor and more animated smacking of the lips. Its intensification was often further expressed by the soft voice sounds. This usually aroused like responses in the sexual object and the play continued until the summation of affect, resulting from the stimulation of most of the major receptor zones, had generated a very active sexual craving. Insertion of the penis into the anus was finally made, followed by rapid strokes and kissing of the lips until mild general convulsive movements resulted. In dogs, rabbits, and sometimes in the case of E, it had been observed that the convulsive movements were followed by a condition not unlike a transitory functional paralysis, in that for some moments walking movements were made with apparent difficulty. The transitory functional paralysis attending a complete orgasm seems to be the ultimate reaction sought for as the erotogenic play advances from one stage to another, and after a period of rest the play begins all over again. Similar functional changes are observed to follow some forms of epileptic convulsions; and psychotics, particularly women, are fond of complaining of their exhaustion after fancied, perhaps hallucinated, sexual relations which are supposed to have occurred during sleep.

Perhaps some observations of the behavior of these monkeys will best illustrate their usual social and sexual behavior.

All the monkeys were mildly hungry when the observations reported here were made.

A, B and C were in a cage together. E was admitted. E mounted A immediately. B tried to touch E's genitalia while E was mounted on A, who had assumed the sexual position for him. E struck at B's hand and B moved behind E. B tried to mount E while E was still mounted upon A. E pushed B away. Then B pulled A away from E and assumed the sexual position before E. E then mounted B. After a few seconds E again mounted A. B pulled A away a second time and substituted himself backing up to E. A then pulled at E's scrotum while E was mounted on B and B barked threateningly at A for interfering. A was intimidated and moved away. B stopped barking. Then A returned again. This occurred several times in a few minutes. Finally A refused to be intimidated by the warning barks, and B's anger became intensified. Evidently A's erotic state was stronger than his fear state although his cautiousness revealed the compromise. Then B scratched A viciously. A screamed and retired. For several minutes A did not take part in the play and showed little spontaneous activity. He was depressed. Later A again started to interfere with the sexual play of B and E and this time E scratched at him. […]

Later B, C and E were playing freely. Suddenly F, who was with D in another cage and watching the play, barked viciously at the players. His barking was of a characteristic kind which was always followed by an assault which frequently terminated in the sexual act. B instantly projected similar sharp, chattering, barking sounds at C. Like F's, his erector spinse muscles were tensely contracted, tail and head were slightly elevated and thrust outward. He also squinted his eyes and smacked his lips.[2] From what followed, his motive was to divert the attention of F from himself to C, but also the sadistic punishment of C that followed generated a marked wave of eroticism in all the monkeys. C gave every evidence of panic. She screamed, exposed her teeth, turned her back and tried to escape. B caught her and bit her savagely. This unusually intense aggressiveness in his behavior may be explained by the fact that B was already the host of intensely erotic motives before this occurred, and erotic motives are always strongly aggressive.

D and F, who had previously been indifferent toward one another, became very active. D mounted F and vigorously attempted to copulate. F continued his barking. E caught B and mounted him, stopping his pursuit of C.

About ten minutes later B again started this peculiar form of assault upon C. This time C promptly projected a similar counterattack upon A, diverting B's attention to A. A became panicky and tried to run away. He exposed his teeth and squealed shrilly. (This panicky behavior seems identifiable with that of men and women who are hallucinating homosexual assaults.) C continued her threats and gradually approached A. E mounted B, while C chased A about the cage, scratching him. F and D, who had ceased playing, now renewed their erotic interests and mounted each other in turn. C continued her vicious pursuit and B continued the same form of barking that was originally projected at C and probably urged her on. B was held by E and could not pursue. Then E released B and reached for A when he came near. Finally E mounted C. C promptly quit barking at A and A at once stopped running. So quickly did his behavior change upon cessation of its stimulus, C's attitude, that he at once returned to E and C, as if to take part in the play. B assumed the sexual position beside C while she was mounted by E, evidently as an invitation to E. Then A chuckled his pleasure, uttering a series of notes identifiable with his expression of pleasure upon acquiring a favorite food.


Sadistic forms of play, such as the persecution of C by B or A by C, as shown by the sexual reactions of the other monkeys had a distinct erotic influence, perhaps an erotic value; and may be comparable to the erotic influence of bull fights, cock fights, dog fights and prize fights so popular with men.

When D and F were admitted to A, B, C and E, F renewed his assault upon B, which was so vicious that B screamed with terror. B's defense was to seek the protection of E by getting behind E and even crawling under him. E struck at F. E has been seen to throw F off the perch to prevent him from reaching B. In this instance F finally caught B, who became catatonic and passively allowed F to manipulate him.

Monkeys will often protect their favorites from persecution by other monkeys even at the risk of severe punishment. The monkey whose protection is sought is usually the sexual favorite. […] 


Sexual favors were frequently offered so as to retain possession of food. Food was occasionally shared with a sexual favorite by a stronger monkey, who at the same time refused some of it to another monkey toward whom he was sexually more indifferent. B would allow A, a sexual favorite, to take food that he had gathered, but would threaten C if she came near. Sexual favorites also obtained protection from assault by other monkeys and frequently sought this protection. […]

Observation. — A, B, C and F were caged together. A piece of apple was handed to B. F tried to grab it. B evaded F and then made sexual overtures to him, smacked his lips and assumed the sexual position for him, but also slyly continued to eat. F did not molest B further.

Another piece of apple was handed to B. F again tried to grab it. B immediately assumed the sexual position and F mounted B. Then B sat up before F and ate his apple openly and unmolested. This procedure was interesting because the sight of food held by a weaker monkey usually invited a prompt assault. Usually the weaker monkey would run away or try to hide the fact that he was holding food. Prostitution is essentially the giving of sexual favors for economic advantages and physical protection. It is interesting to note that in man so soon as the sexual favor is spontaneously offered for its true affective value, the social censorship weakens. […]


[…] Sexual reinvigoration may promptly occur upon presentation of a new sexual object of adequate type. For example, after D and E had been caged together for several days they became sexually indifferent to one another, for little or no sexual play occurred. Then when C (a comparatively inappropriate sexual object) was admitted they did little more than bluff her by staring and growling at her. C promptly isolated herself by going into a corner. When B was admitted, almost immediately E began to play with B, mingling overt sexual acts with playful wrestling until the affective state was one of marked eroticism, as manifested by their persistent attempts at copulation. Hamilton has observed similar phenomena, and has reported that monkeys, when they are sexually semi-fatigued, expose their erotogenic receptors to intensive stimulation of an adequate nature before copulation recurs, and yet the same monkey in such a condition of sexual indifference to his companion, if allowed to have another mate, may rush into a sexual embrace with great excitement and without previous stimulation; apparently reacting to the new stimulation of his distance receptors. Similar behavior also occurs in man; […]


[…] Upon the differences in inherent sexual selective tendencies McDougall says that Professor Freud “would explain the direc­tion of the sex impulse of man toward woman by the assumption that the male infant derives sexual pleasure from the act of suck­ing at his mother's breast. It is, I submit a sufficient refutation of the view to ask: How, then, does the sex instinct of woman become directed towards man? How explain the fact that homosexuality is not the rule in women?”[3]

If men are similar in their phylogenetic constitution to the male monkeys, as studied by Hamilton and myself, where the tendency towards homosexuality precedes and predominates the tendency towards heterosexuality, a condition which was not usual with the females, then McDougall’s question may be answered by the obser­vation that males and females apparently do not begin with the same selective tendencies. In males there is apparently an inherent pre­disposition to particular sexual interests which include those of a homosexual nature, as well as a predisposing selective tendency to acquire the female which has a secondary value to the homosexual interests for a certain period of years, during which time the homo­sexual tendencies may become fixed. […]

The sexual interests of male monkeys which have not reached the adult stage, as above indicated, are much more related to the same sex than to the opposite sex. The tendency seems to be towards an increase of interest in the opposite sex after the adult development has been reached, but even then the total or even a very decided abandonment of homosexual interests has not been observed. Because of its uniform occurrence during the growth of monkeys, the precedence of the homosexual stage to the heterosexual must be considered normal in the evolution of the individual. Perhaps this is partly due to competition for mates and punishment of the weaker rivals, the young males and females. The homosexual as well as the heterosexual functions appear to be developed through experience. F tried to find C’s genitalia where he found the genitalia of males. D, E and F were larger than A, B and C and had to learn how to accommodate to the stature of the smaller monkeys in order to perform the sexual act. A, B and C had to learn that sexual favors procured protection, food and immunity from assault. Pain and unpleasant experiences, fear and hunger inhibited the sexual interest, while pleasant conditions were conducive to free play of the sexual interests. C, the young female, was comparatively rarely sought as a sexual object. All five males showed much more interest in their own sex, but this may have been due to C’s youth. Hamilton found that regression to the homosexual interests as a rule occurred quickly upon removal of the female or with the possibility of punishment by a dominant male. This seems to be comparable in man to the homosexual who dreams of affectionate relations with his mother (a fixed, unattainable, definite, heterosexual object, and hates his dominating father).

In man the universal precedence of overt or disguised homosexual interests during the growth of the individual is recognized as normal. The gradual transfer to heterosexual interests has been found, through the analysis of a large series of men and women, to be a delicate functional procedure with a constant liability to regression to homosexual interests until a thorough heterosexual transfer is made. If, because of the absence of a heterosexual object or painful heterosexual interests and fearful experiences such as disappointment in love, fear, pain, disease, etc., regression to the preceding homosexual affections occurs, the interests tend to become unmodifiably fixed after a certain age (about thirty ?) . Homosexual fixation and heterosexual failure is in a large group of individuals determined by the organic constitution of the individual, but a still larger functional group of males and females, who are organically normal, have had their sexual reflexes so “conditioned” by pleasant and unpleasant experiences that, despite all conscious wishes to regulate them, they have become fixed homosexual types.

Fixation at the homosexual level in either sex is recognized as a biological failure and is the cause of, in many cases, the gravest states of anxiety, with perhaps complete wrecking of the personality or suicide. Many individuals, after they have developed a comfortable margin of heterosexual affective tendencies, when they recall their past homosexual interests, experience so much unpleasantness that they vigorously censure anything, whether scientific or not, that may influence this recall. [A paragraph expanding on this human reaction is here omitted]

Some of the most profound and irrecoverable tendencies to chronic dissociations of the personality are based upon the fearful anxiety caused by complete sexual inversion. Why it is universally considered to be more “effeminate,” “manly” or “deficient” to be the homosexual object than to be the homosexual patron seems to have its foundation farther back in the phylogenetic scale than the influence of social culture. Hamilton observed eleven monkeys at large for several weeks and never observed that a sexually mature uncastrated monkey assumed the sexual position for copulation with a weaker fellow. In my band of monkeys the stronger male was never observed to assume the female sexual position until he had gratified his desires. The degree of eroticism and strength as firmly determined sexual play as the degree of hunger and strength determined the acquisition of food. Homosexual submission in monkeys seems to be a form of expressing submission to a stronger monkey’s power which would necessarily imply inferiority. A, B and C often assumed the sexual position before a stronger monkey when he became aggressive and he would usually stop his threats. Sexual inverts tend to become decidedly submissive in voice and manner.

Probably the irrepressible sexual craving to assume the female role in the sexual act causes so much distress because the individual’s other wishes, namely to be “manly,” “strong,” biologically as potent as others, are so seriously conflicted with and belied.

Hamilton observed that eunuchs, although they attempted copulation with females, would assume the sexual position for smaller and weaker males. On the other hand, he noted that in two monkeys who arrived at sexual maturity at about the same time, one would as likely assume the sexual position as the other. E and D tended to do this also, especially after several months of sexual play, but whenever E and D were apparently equally erotic E dominated D. Patients, while in the panic stage of sexual inversion, often believe that they will be castrated (rendered impotent) and forced to become the sexual object of a more powerful male (father imago).

The homosexual behavior of the infrahuman primates clearly shows that comparative inferiority, physical weakness and biological impotence are acknowledged by the sexual object in his submission to the wishes of the aggressor. This, as an inherent characteristic, may be the biological root of the grave distress shown by men and women who cannot modify their tendencies to submit themselves as homosexual objects (biologically unproductive, hence perhaps censured by the species). [More on adult human inverts is here omitted]

Hamilton is inclined to believe, even though homosexual play is preferred to heterosexual play in immature males, since it is less freely indulged in after maturity and relatively more heterosexual play occurs, that in their native habitat homosexual play may be altogether abandoned after maturity. The probability that homosexuality is very essential to the macaque for the development of his sexual functions and gregarious tendencies is suggested by the fact that the five males under my observation showed so much more sexual interest in one another than in C, even during what seemed to be her menstrual periods when she was most erotic.

In man homosexual interests occur so universally during the growth of the individual that, if considered in relation to his phylogenetic history, they must perform a very important biological function and should be given the most careful consideration in the near future in order that we may understand their psychological significance.

Monkeys, baboons and probably apes, children and many adults of both sexes, when erotic are bisexual and ambivalent in that they may become either the sexual object or the sexual patron, depending upon the influence of the sexual companion. In either instance the individual is in reality aggressive in the sense of seeking stimuli that will neutralize his or her affective state, even to forcibly removing competitors as in the reported behavior of B and A with E.


When the monkey is not hungry and is sexually fatigued his acquisitive faculties are in their lowest stages and, provided that he is not uneasy about his safety, he is contented to sit quietly in a corner and sleep. […] It is surprising, however, how energetic he is and what tremendous curiosity he has when he is sexually hungry even though not food hungry. He investigates everything, seems to be particularly fond of holes, crevices and movable objects, and likes to play. He apparently reacts with sexual affect to a large variety of animated objects in his environment that do not cause fear, such as cats, dogs, foxes, guinea-pigs, snakes, men, children, etc. All seem to be more or less appropriate stimuli for his sexual acquisitive faculties, especially if he may play with and examine them. The examination may have an erotogenic influence.

Since the social favorites of the monkey are also his sexual favorites, does it mean that his social interests are but preliminary forms of play which, if adequate, will lead to overt sexual play? Are social and sexual interests identifiable? If the term sexual is applied to all forms of play that may eventually lead to marked eroticism and overt sexual acts, it includes practically every form of behavior that may be called social except that of mutual protection, assistance in supplying food and migration.

[…] Monkeys seem to adopt one another as companions for the libidinous pleasures that they give each other.


[…] Upon the other hand much of the universal element of hatred, anxiety, persecution and distrust that largely determines the present constitution of our social system results from the discomforts caused by our unintelligent persecution and suppression of our vital biological needs. […]


In the infrahuman primates as well as in the genus Homo, homosexual interests predominate and normally precede heterosexual interests until the adult stage is well established. Homosexual interests occur in both sexes but are more common in the male.

The acquisition of an adequate sexual object for the affective cravings promptly proceeds if it is not inhibited by fear.

The transfer of the affective cravings from a homosexual type of object to a heterosexual object is a very delicate biological procedure and one that must not be inhibited by fear.

Reversion to homosexuality in isolated groups of males or females, such as prisoners, soldiers and sailors, normally occurs if adequate outlets for sublimation are not provided.

Submission as a homosexual object is implicated with biological inferiority in the infrahuman primate. This is probably the phylogenetic root of man's conscious, ineradicable recognition of homosexuality as a biological deficiency.

In the infrahuman primate as in man, sexual submission is practised in order to procure food (clothing), and protection.

Catatonic adaptations are reflexly practised by the infrahuman primates as well as by the human primate as a defense.

[…] Probably nothing else so much as the failure of psychiatrists to recognize the true nature of the affective needs of individuals has obscured our insight into the psychogenic psychoses and neuroses. The phylogenetic constitution of man, as we find it completely exposed in the infrahuman primate, obsesses him with what he feels to be perverse tendencies as he strives to behave in an ideally civilized manner and plunges him into the depths of despair when he fails. […]


[1] G. V. Hamilton: A Study of Sexual Tendencies in Monkeys and Baboons. Jour. Animal Behavior, Vol. IV, No. V, pp. 395-318. [Author's footnote]

[2] Strikingly similar squinting of the eyes and smacking of the lips (but of course more suppressed) were observed in the homosexual advances made by two American diners to several Hawaian serenaders in a ship's dining saloon. [Author’s footnote]

[3] McDougall, W.: An Introduction to Social Psychology. Eighth edi­tion, Supplementary Chap. II, p. 398. [Author’s footnote]




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