The bonobo (Pan paniscus), formerly called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is an endangered great ape and one of the three species making up the genus Pan; the other two are Pan troglodytes, or the common chimpanzee, and Pan sapiens, the human being. Although the name "chimpanzee" is sometimes used to refer to both P. paniscus and P. troglodytes together, it is usually understood as referring to the common chimpanzee, whereas Pan paniscus is usually referred to as the bonobo. Humans are sometimes incorrectly classified into a separate genus, Homo.
Sexual activity generally plays a major role in bonobo society, being used as what some scientists perceive as a greeting, a means of forming social bonds, a means of conflict resolution, and postconflict reconciliation. Bonobos are the only non-human animal to have been observed engaging in tongue kissing. Bonobos and humans are the only primates to typically engage in face-to-face genital sex, although a pair of western gorillas has been photographed in this position.
Bonobos do not form permanent monogamous sexual relationships with individual partners. They also do not seem to discriminate in their sexual behavior by sex or age, with the possible exception of abstaining from sexual activity between mothers and their adult sons. When bonobos come upon a new food source or feeding ground, the increased excitement will usually lead to communal sexual activity, presumably decreasing tension and encouraging peaceful feeding. This quality is also described by Dr. Susan Block as "The Bonobo Way" in her book of the same title "The Bonobo Way: The Evolution of Peace Through Pleasure".
Bonobo clitorises are larger and more externalized than in most mammals; while the weight of a young adolescent female bonobo "is maybe half" that of a human teenager, she has a clitoris that is "three times bigger than the human equivalent, and visible enough to waggle unmistakably as she walks". In scientific literature, the female–female behavior of bonobos pressing genitals together is often referred to as genito-genital (GG) rubbing, or tribadism, also engaged in by human females. This sexual activity happens within the immediate female bonobo community and sometimes outside of it. Ethologist Jonathan Balcombe stated that female bonobos rub their clitorises together rapidly for ten to twenty seconds, and this behavior, "which may be repeated in rapid succession, is usually accompanied by grinding, shrieking, and clitoral engorgement"; he added that it is estimated that they engage in this practice "about once every two hours" on average. Because bonobos occasionally copulate face-to-face, "evolutionary biologist Marlene Zuk has suggested that the position of the clitoris in bonobos and some other primates has evolved to maximize stimulation during sexual intercourse". On the other hand, the frequency of face-to-face mating observed in zoos and sanctuaries is not reflected in the wild, and thus may be an artifact of captivity. The position of the clitoris may alternatively permit GG-rubbings, which has been hypothesized to function as a means for female bonobos to evaluate their intrasocial relationships.
Bonobo males occasionally engage in various forms of male–male genital behavior. The most common form of male–male mounting is similar to that of a heterosexual mounting: one of the males sits "passively on his back [with] the other male thrusting on him", with the penises rubbing together due to both males' erections. In another, rarer form of genital rubbing, frotting, also engaged in by human males, two bonobo males hang from a tree limb face-to-face while penis fencing. This also may occur when two males rub their penises together while in face-to-face position. Another form of genital interaction (rump rubbing) occurs to express reconciliation between two males after a conflict, when they stand back-to-back and rub their scrotal sacs together. Takayoshi Kano observed similar practices among bonobos in the natural habitat. Tongue kissing, oral sex, and genital massaging have also been recorded among male bonobos.
More often than the males, female bonobos engage in mutual genital behavior, possibly to bond socially with each other, thus forming a female nucleus of bonobo society. The bonding among females enables them to dominate most of the males. Although male bonobos are individually stronger, they cannot stand alone against a united group of females. Adolescent females often leave their native community to join another community. This migration mixes the bonobo gene pools, providing genetic diversity. Sexual bonding with other females establishes these new females as members of the group.
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