Monkey Sexuality?

Tilda Sutter

The Real Monkey Business

Prof. Joyce Powzyk

April 17th, 2023

Bonobos, Chimpanzees, and Human Sexuality

The origins of human behavior continue to confound primatologists. As humans share a common ancestor with chimpanzees, their aggressive, patriarchal society serves as the dominant model for our habits. However, their egalitarian primate counterpart, bonobos, also employ mannerisms that mirror that of humans. These differing manners of relation have sparked debates about the true primate origin of human behavior. By comparing the evolutionary motivations of both bonobos and chimpanzees, the nuances of human desire are illuminated. 

The inequality of food resources between chimpanzees and bonobos compromises their differences. Bonobos inhabit areas with an abundance of fruit, minimizing competition over resources. Therefore, male bonobos can afford to share their produce with female and juvenile members of their populous natal group. These apportionments facilitate an egalitarian relation between sexes. Similarly, the availability of fruit negates the need for male cohorts of hunting, evening their male ranking system. This abundance of resources allows for relatively large natal groups, with minimal hierarchization. 

Chimpanzees populate forests with scarce resources, enhancing the innate competition over assets. Male chimpanzees are territorial over their yields, rarely sharing with females or other members of their comparatively small natal groups. Males also organize themselves according to a strict hierarchical structure, ensuring the allocation of resources to the alpha male. Male cohorts hunt red colobus monkeys to bond and strengthen their ranking system (Mitani and Watts, 2001). This arrangement is mutable; it creates frequent violent, male on male attacks for dominance. Unlike bonobos, females feed in small groups or alone, and they tend to not form lasting bonds. 

These varying ecological pressures extend to the sexualities of chimpanzees and bonobos. While both species are promiscuous, characterized by every male mating with all females, the function sex serves differs by primate. Bonobos are constantly receptive to sex for purposes beyond reproduction. Sexual activity eases tension and facilitates bonding between individuals - even mothers and daughters are often observed engaging in genital rubbing. Mating is not relegated to heterosexuality; females bond through sexual activity, not bloodlines. These alliances create the cooperation required for altruistic child raising. The regularity of sex fuels their egalitarian relations, and allows encounters between individuals to be predominately peaceful. 

In addition, bonobos’ physicality suggests an innate desire for pleasurable, not reproductive sex. Female bonobos have visible and continuous sexual swelling, ensuring their constant availability to mate. Both male and female bonobos may have developed ventrally located genitals due to their bipedal walking, guaranteeing the accessibility of casual sexual activity. Their lack of sexual dimorphism also indicates a balanced relationship between sexes.  This egalitarian, sexually experimental society is incongruous with chimpanzees’ mating system. While chimps are promiscuous, females only exhibit visual sexual swelling every thirty-five days, ensuring that sexual activity is less frequent and directly related to reproduction. Chimpanzees are sexually dimorphic, and males assault all female members of their natal group in order to reach sexual maturity. Females do not mate with one another and do not form bonds beyond their bloodline. This aggressive and patriarchal form of sexuality mirrors the intense competition over food experienced by chimpanzees. 

Humans typically form heterosexual pairs, and are classified as monogamous. Monogamy ensures that fathers participate in child-rearing, increasing the chances of survival and reproduction for their offspring. As human infants are highly altricial, they require more care than newborn bonobos and chimpanzees. Human females exhibit concealed ovulation, requiring a male to couple with a female throughout her ovulation cycle to secure parenthood. However, the nuances of human desire complicate an understanding of primate sexuality. Humans tend to be behaviorally polyandrous, through affairs and mistresses. When male humans amass an abundance of resources, they are able to support multiple partners, increasing their chances of reproduction. 

Human sexuality may not be solely for reproduction, as many people form same-sex partnerships or refuse sexual activity altogether. This perceived indifference towards reproduction has sparked theories about the evolutionary purpose of homosexuality in humans. 

One model suggests that bisexual primates are more likely to reproduce, however, this fails to explain strict homosexuality. Some scientists suggest that homosexuality may increase the commonality of alloparenting. As humans are highly altricial, they need more care than infant bonobos and chimpanzees, and may require attention from non parental relatives (Bawagan, 2018). This altruistic child raising mirrors the function of female-to-female sexual activity between bonobos, suggesting that homosexuality facilitates the cooperation necessary for child-rearing. These interpretations are not mutually exclusive, and it is likely that there are other evolutionary advantages to homosexuality. However, the concept of sexual orientation and gender identity is an exclusive aspect of human behavior that cannot be compared to any other primate species.

Human sexuality encompasses elements of both bonobo and chimpanzee reproductive strategies. Like bonobos, humans use sex for purposes other than reproduction, to ease tension and form bonds. While the fluidity and frequency of human sexuality may mirror bonobos, human sexual dimorphism indicates a relation to chimpanzees. Male chimpanzees developed to dominate their female counterparts, to guarantee access to scarce food resources. The frequency of human polyandry could suggest a similar human system of reproduction - one focused on the male’s amassing of resources. Human females’ relative slendering may also indicate subordination, and serves as a possible explanation for the prominence of the patriarchy in sexuality. 

Sexuality aids in the formation of close bonds, like bonobos, but also institutes strict patriarchal systems, like chimpanzees. Homosexuality in humans, however, provides a stark divergence from these evolutionary forces. Recent investigations into the evolutionary advantages of same-sex partnerships will illuminate the nuances of sexuality not experienced by non-human primates.  

Works Cited

"Scientists explore evolution of animal homosexuality." Imperial College London, 4 Oct. 2018, https://www.imperial.ac.uk/news/190987/scientists-explore-evolution-animal-homosexuality/.

Mitani, John C. and David P. Watts. "Why do chimpanzees hunt and share meat?" Animal Behaviour, vol. 61, 2001, pp. 915-924. doi: 10.1006/anbe.2000.1681.