So… Should Humans Be Monogamous?

In all of the previous posts, I have refrained from using information and examples from human studies. This is because it is crucial to understand why monogamy might occur evolutionarily and how it occurs in other species before attempting to add in the complexities that human sociality may bring into the science. There is much debate on the topic of human monogamy. Perhaps people that are discomforted and baffled by the prevalence of cheating and failed marriages seek an answer that explains these phenomena. Books such as Sex at Dawn (which is a NY Times best seller) have horribly misquoted and misinterpreted science to advocate for the social acceptance of open marriage. Some people in the field of ethology were highly upset – one so much that she (Lynn Saxon) wrote a book in response, titled Sex at Dusk, practically tearing apart the arguments presented in the former one by one, and ultimately presenting evidence for humans being serial monogamists (which doesn’t necessarily imply 100% monogamous behavior).

            Despite the prevalence of cheating and failed marriages in humans, it seems that many of the biological mechanisms facilitating monogamous behavior have been preserved in humans. One example lies in the hormonal fluctuation of women. Estrogen has been shown to promote sexual behavior in many animal models such as rodents, and has been linked to sexual desire in women. After ovulation, (when progesterone levels increase) there has been much debate about whether progesterone levels are correlated with a general decrease in sexual desire, or a decrease in extra-pair sexual desire and an increase in in-pair sexual desire. To test this, researchers compared in-pair and extra-pair desire of pregnant women who met their partner either while on hormonal contraceptives, or while regularly cycling. Results indicated that pregnant women who met their partner while on hormonal contraceptives had higher levels of in-pair desire compared to pregnant who met their partner while regularly cycling (Cobey, Havlíček, Klapilová, & Roberts, 2016). The opposite effect was not found. In other words, extra-pair desire was not significantly different in pregnant women who met their partner while not on hormonal contraceptives. Increased in-pair desire being correlated to the period of time after ovulation in past studies and to pregnancy and hormonal contraceptive use in this study seems to be no coincidence. Perhaps less estrogen and/or more progesterone facilitates behavior that increases the chances of more biparental care (in this case, “behavior” being loyalty from females).

            Testosterone also changes in a way that can facilitate monogamous behavior in humans in the right context. For example, compared to men who are single or in a new relationship, men in a long-term relationship (more than 12 months) had significantly less testosterone (Farrelly, Owens, Elliott, Walden, & Wetherell, 2015). This could serve as a way to decrease sex-drive and increase effort put towards the partner and offspring. Another study showed that both testicular volume and testosterone levels were inversely correlated with parental caregiving (Mascaro, Hackett, & Rilling, 2013). This agrees with research that has shown more polyamorous species  have testicles larger in volume compared to species considered close relatives. Another interesting finding from this study was that an area of the brain called the ventral tegmental area (which is associated with reward circuitry) showed increased activation when parents were shown a photograph of their own child compared to another child (Mascaro et al., 2013). This has implications in many contexts, such as in the treatment of step-children. No matter how hard a step-parent may try, maybe it is biologically impossible for them to have the same love for their step-children as children of their own. To my knowledge, this is just a discussion point, and has not been studied directly.

            Peptide hormones such as oxytocin seem to also play a role in human monogamy. Researchers found that compared to single men, men in a relationship remained a significantly greater distance away from an attractive female upon first exposure (Scheele et al., 2012). Oxytocin has been known to increase due to involvement in a monogamous relationship. However, more recent studies such as this give further explanation as to how oxytocin could promote monogamy and fidelity.

            In many ways, human biology seems to be set up to facilitate monogamous behavior in specific contexts. Just because people cheat doesn’t mean that monogamy appeared with such force in humans by mistake. Many animals that are socially monogamous have extra-pair relations, and humans seem to be no different in that respect. Polyamorous behavior in humans being the primary strategy is implausible due to many reasons, including uncertainty of paternity, and the unlikelihood of people freely sharing resources. Feelings of jealousy aren’t absurd and selfish – but have naturally evolved for things such as certainty of paternity (males) and ensured resources from partner (females).


Cobey, K. D., Havlíček, J., Klapilová, K., & Roberts, S. C. (2016). Hormonal Contraceptive Use During Relationship Formation and Sexual Desire During Pregnancy. Archives of Sexual Behavior, 45(8), 2117–2122.

Farrelly, D., Owens, R., Elliott, H. R., Walden, H. R., & Wetherell, M. A. (2015). The Effects of Being in a “New Relationship” on Levels of Testosterone in Men. Evolutionary Psychology, 13(1), 147470491501300130.

Mascaro, J. S., Hackett, P. D., & Rilling, J. K. (2013). Testicular volume is inversely correlated with nurturing-related brain activity in human fathers. Proceedings of the National Academy of Sciences, 110(39), 15746–15751.

Scheele, D., Striepens, N., Güntürkün, O., Deutschländer, S., Maier, W., Kendrick, K. M., & Hurlemann, R. (2012). Oxytocin Modulates Social Distance between Males and Females. Journal of Neuroscience, 32(46), 16074–16079. )ܓ+��x� ‘.W

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