The socio-sexual behavior of female bonobos confers upon them several advantages. One aforementioned benefit is the ability of unrelated bonobos to form close bonds to facilitate the transition from the natal to the adult group during dispersal. Females can then band together to better defend themselves against harassment by males. Although males rarely behaved submissively toward young females, they were submissive when faced with a group of females (Kano 1986). Thus the pattern of gg rubbing among bonobo females may serve the purpose of forming alliances to protect one another (de Waal 1995).

Additionally, the sexual receptivity of female bonobos to male bonobos influences the operational sex ratio, skewing reproductive choice in the favor of the female bonobos. Female chimpanzees show estrus for 5% of their lives while bonobos show estrus for 27%. This difference in female receptivity translates to an operational sex ratio of 2.8 in bonobos and 4.2 (when there are few males) – 12.3 in chimpanzees (Furuichi 2011). The lower operational sex ratio in bonobos means that there will be less intrasexual competition among males for access to females. Female mate choice, therefore, becomes the most important factor in determining whether a males genes are passed. Perhaps for this reason, there have been no reports of forced copulation among bonobos. The elevation in the importance of female mate choice translates to high social status for bonobo females as compared to their chimpanzee counterparts. Evidence for this elevation in social status is provided in the low number of agonistic encounters that do occur; females were dominant in as many situations as males. Hohmann (2000) has suggested that sociosexual behavior may be a low cost expression of dominance.

Lowered competition for access to mates also translates to lowered competition for access to resources; males who do not have to compete do not need to invest extra energy in getting large to ensure their reproductive success. Feeding is most often the context for sexual encounters among bonobos, indicating that the potential tension caused by competition over food triggers the expression of the behavior. This tension is resolved by the sexual behavior of bonobos in so far as it facilitates sharing. High status males will share prized food with females, yet males rarely shared food among themselves (de Waal 1995). In situations where a dominant female was approaching, males often yielded preferred positions at feeding sites to the late-arriving female (Furuichi 2011). In many cases, food sharing will occur immediately following a sexual encounter.


The primarily function of sociosexual behavior is to reduce tension generated by potential competition for the prized food. Blount (1990) reports that males in possession of prized food appeared nervous when approached by others, providing more evidence for the role of sexual interactions in tension reduction. This tension can be explained by the remaining competition for highly prized foods because of the preference for nutrient rich foods and the large group size (Sommer 2010). In the absence of these highly prized foods, there is little tension observed and food was shared freely (Susman 1984). Reducing unnecessary competition for food is advantageous in an environment that is resource rich because it minimizes the costs of elevated levels of aggression, yet certain foods will always be preferred. Bonobos resolve this issue by introducing socio-sexual behavior to aid in the distribution of food.

Sociosexual behavior also plays a role in shaping the structure of bonobo society itself. As previously mentioned, this behavior elevates the social status of females. Because paternity in such a situation is impossible to determine, the rank of bonobo males is matrilinear by necessity. The only permanent bond in bonobo society is that between a mother and a son. Males remain reliant on their mothers for support in agonistic situations as adults. Thus males that are sons of prominent females will be higher in rank than either new arriving females or other males. Dominance in bonobo society therefore, is not distinguished solely by gender, but rather by the complex relationships between females and their sons.

Figure 4. Sexual relations among chimpanzees and bonobos. Females are drawn in upper parts, males in lower parts. Dark colors show estrous females and alpha males. Arrows show the solicitation or acceptance of copulations

Differential Reproduction:

Differential reproduction is the idea that organisms that are best suited to their environments will survive to reproduce and leave offspring of their own. As a result of females staying in mixed groups regardless of their estrus state, prolonged female receptivity leads to a reduction in sexual competition between males. Sexually attractive females in pseudo-estrus spend much of their time in bonded groups with other females, making it more difficult for a single male to monopolize any one female. Sexual competition amongst male bonobos consequently is reduced, lending to a lower infant mortality rate in bonobos relative to chimpanzees, as much of the harmful behaviors directed at female chimpanzees by the males (such as herding, infanticide, physical violence, etc), is avoided in bonobos (Furuchi 1988a). With less resources being spent on sexual competition and the constant production of offspring, bonobos are able to invest more time and resources into the quality of their surviving offspring and increase the infant’s chance at survival (De Lathouwers et al. 2005).