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Clarence Ray Carpenter (1905-1975) was a research professor of psychology and anthropology, Pennsylvania State University, 1940-1970, and University of Georgia 1970-1974. His first published article concerning primate behavior appeared in 1934 and, according to Harvard's Irven DeVore, for the succeeding thirty years almost all of the accurate information available on the behavior of monkeys and apes living in natural environments was the result of Carpenter's research and writing. In addition, he was responsible for the production of primate films and videotapes, the establishment of Penn State University as a depository for the Psychological Cinema Register and for developing an internationally known collection of psychological, psychiatric and animal behavior films.[1]

Carpenter's "Sexual Behavior of Free Ranging Rhesus Monkeys (Macaca mulatta)" was published in the Journal of Comparative Psychology, 33(1), in 1942, from which the following extracts are taken. They include some introductory information along with the entire section "Homosexual Behavior in Males".

I. Specimens, Procedures, and Behavioral Characteristics of Estrus


[...] Though this primate type has been extensively studied in laboratories, recent observations of it in a free range situation have yielded important supplementary facts. It is the purpose of this article to describe definitively the sexual behavior of Rhesus monkeys living in free ranging groups on a small island of Puerto Rico.

C.R. Carpenter on board deck of a Cunard liner en route from India to New York with rhesus monkeys destined for Santiago Island (pictured right), 1938


The Island offers a situation which, in many respects, is uniquely favorable for a breeding colony of Rhesus monkeys. Here, according to original plans, field and laboratory research were to be closely integrated.


The original stock of the Santago Colony was collected by the author in India during September, 1938. Three months later, 409 monkeys were released on Santiago Island. On March 1, 1940 the Rhesus Colony had about 350 monkeys in various stages of development ranging from infancy to senility. There were 24 adult males and four sub-adult males who lived in heterosexual groupings, while 12 sub-adult males lived in unisexual male groupings, thus making a total of 40 males in the Colony. [The remainder consisted of roughly 150 adult females and 160 infants.]

II. Periodicity of Estrus, Homosexual, Autoerotic and Non-Conformist Behavior

Ismael Solis Arroyo, 12yo local boy who joined the Santiago team from its inception, releasing a monkey of the founding stock, December 1938


The data used in this study were collected during a period of almost continuous, daily and systematic observations on Rhesus monkeys of the Santiago Colony. The observational field work was done between 6:30 a.m. and 4:00 p.m. each day from February 29 to April 27, 1940.



The Santiago Rhesus Colony, as was suggested in a previous paper, is made up of heterosexual groupings and unisexual male groupings. In June, 1940 there were two of the latter type of groupings, one having seven and the other twelve young males, each of the individuals varying in stages of developments from early juvenile to early adult stages. Typically, for these Rhesus monkeys the young male separates from his parent group during early adolescence, with few exceptions,[2] and lives in unisexual groupings along with other young males until early adult life. At this age, he gradually leaves the male group, and enters a heterosexual group, where he passes through various stages of subordination until he is tolerated within, and later becomes an integral part of the heterosexual group. When his mature status has been established, he has access to food, to estrous females and to preferred spacial positions within the group at the discretion of more dominant males. Later he may eventually become the autocrat of the group.

Members of the founding stock of rhesus monkeys on Santiago Island, 1939

During the association in the unisexual grouping, the number of mountings of one young male by another is even accentuated over the number to be observed during the previous periods of late infancy. The pattern of mounting resembles that of normal adult males and females. Though the mounting may involve anal penetration, the act is not carried out in series and no evidence is as yet available to show that ejaculation takes place. The mounting pattern is stimulated by a variety of situations such as active play, an aggressive approach by another of the young males, general excitement, for example, the stimulation of a nearby fight, or the close approach of an observer. The more dominant individuals play the masculine role while the more subordinate monkeys usually enact the part which corresponds to the female role. As in female-male relations, attacks may be foiled when the object of the attack suddenly presents and thus diverts the aggressor from attacking and stimulates him to mount instead.

These unisexual groups are not only structured along a dominance gradient which is regulated by aggressiveness and competition but also there  seems to be some tendency for the young males to pair off, to travel in pairs and to fight cooperatively.

If the mounting of one young male by another be termed homosexual behavior, then the activity is to be observed most frequently in these unisexual groupings. There may be some question, however, about the validity of this definition of homosexuality since the behavior could be a stereotyped and patterned response with a low threshold of non-specific stimulation for sexual behavior. Among other things it seems to be an outlet, at times, for aroused by displace instigation for fighting.

Famous “Misogynist” photo of a solitary adult male rhesus standing in the water between Santiago Island and mainland Puerto Rico (LIFE Magazine, 16 Jan. 1939)

Among the males in organized, heterosexual groups, even between males which have access to females, homosexual mountings occur. Such behavior is to be observed most frequently between very subordinate males or between tangenital [sic] and subordinate males. Nevertheless, it also occurs between the more dominant males in the group. Young males who are gradually becoming more closely associated with a heterosexual grouping, seem to gain the tolerance of subordinate males at first, among other things, by submitting to being mounted. Subordinate males who stay close together and fight cooperatively against attackers, frequently mount each other during the excitement of aggressive action. The tension and emotional excitement which persistently characterize these subordinate animals with insecure social status seem to be important factors in provoking homosexual mountings.

Among the more dominant males [...] mountings seem to express an affinitive or "friendly" quality of the relationship and at times a kind of greeting response. As far as could be observed, none of these mountings stimulated ejaculation and hence there is some doubt as to its being an expression of true sexual behavior. The problem should be investigate experimentally.

Other kinds of deviate sexual behavior in female Rhesus monkeys should be described at this point. Once an old female was observed attempting to mount male 160-1 [top ranking male of his group] in a situation in which 160-1 was unresponsive and the female was sexually excited and disturbed. 160-1 responded by mildly attacking the female. Again, an estrous female forcibly put a juvenile male into position and mounted him in a situation of general excitement.


[1] This is a modified extract taken from Penn State University Libraries.

[2] There was a young, well developed and very tame juvenile male which lived in Group IV and moved within the sphere of protection of 156-2 [second-ranked adult male]. 156-2 was a gentle, mature but young adult. Likewise another juvenile of about the same age lived in Group II, but I could not observe any special relationship with the more dominant males. He was simply tolerated by them. A juvenile which I castrated in January, 1939 was a member of the largest unisexual male grouping. In June, 1940 he was badly wounded on the arms but I did not learn which individuals attacked him. [Author's footnote]



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