Commitment Issues? There’s more science to it than you think
by Naimisha Kodali
Franklin College of Arts and Sciences, Department of Genetics
Considering the evolutionary concept of fitness, the medium for reproduction in humans, monogamous relationships, may not seem effective. Other forms (polyamory, promiscuity, etc.) may seem more effective to produce more offspring. New models however have found evidence that this evolution of monogamy may have resulted from the rise of grandmothers, explained by the grandmother hypothesis, and mate-guarding. As the menopausal age range rose, women started taking on the roles of grandmothers. This encouraged mothers to mate again, attracting older men. Despite the older men reentering the mating pool, there is a higher supply of men compared to women. This prompted mate-guarding to evolve, where man must keep his woman is through commitment, exclusivity, and active guarding from other males. This allows him to have more children, passing the tendencies on to further generations so that monogamy can evolve. Furthermore, to mitigate further competition and facilitate this familial structure, the tenets of love, care, and trust in relationships were positively selected for. This model explains how humans have evolved to form monogamous relationships and the current foundation for dating, marriage, and social structures.
Monogamy, Grandmothers, Evolution, Mating, Relationships, Genetics
Monogamy is weird. Dr. Dieter Lukas, a prominent evolutionary biologist from the University of Cambridge, even called monogamy, or what we call commitment to a singular person in a relationship, a “problem” and told reporters at a conference that biologists consider it an evolutionary puzzle (Zimmer, 2013). From an evolutionary standpoint, any other system for reproduction would be seemingly more beneficial for humans. If men and women could mate whenever and be with whomever they want, without any rules about commitment to a singular person, the human population would be even larger by now.
We are one of the very few species that have a track record of monogamy, with only 10% of species in the world practicing exclusive mating (Lukas & Clutton-Brock, 2013). However, new research shows that we have evolved to adopt monogamy and commit to relationships due to one major factor: grandmothers (Schacht & Bell, 2017). This relationship between grandmothers and their influence on the evolution of monogamy comes from the merging of two powerful concepts, the grandmother hypothesis and the mate-guarding hypothesis.
Are grandmothers evolutionary matchmakers? Since women live far past their menopausal age- the age at which they can no longer have children- they can help raise their grandchildren (Coxworth et al., 2015). It should be noted that this dynamic is not very common in other species, nor is living past reproductive age. That’s right, grandma babysitting you while you bake cookies with her has an important role in why commitment evolved in humans.
When women have help from grandmothers in raising their children, they can recover faster from childbirth and childcare, and become available to have more children sooner. This additional support allows mothers to return to the dating pool faster. Similar to how the age range preferences we choose on Tinder and other dating apps tend to widen as we get older, these mothers often consider both older men and younger men as potential mates. The older men were previously too old for the younger women, but are fair game to the mothers, thanks to grandmothers helping out. This situation encourages a lot of men to reenter the dating pool. Additionally, the average age at which women cannot have children anymore is 45 years, whereas men can technically have children until the end of their lives, which means that there is a higher supply of men than women in this dating pool regardless.
Thus, older men are now in competition for women with men their age and younger, so the best way for a man to “win” his woman is through committing to her and hence actively guarding her from other promiscuous males (Schacht & Bell, 2017). If he commits to her and takes care of her, while actively keeping other men away, then he can have more children who will then pass his genes on, along with his inclination towards commitment, which is an example of fitness. On the other hand, since there aren’t enough fertile women for all the men available, other men who do not guard their women will have less of an opportunity to pass their genes on, so their promiscuous tendencies are also less likely to get passed on (Coxworth et al., 2015). This strategic advantage that is enabled by grandmothers is referred to as the mate-guarding hypothesis (Schacht & Bell, 2017).
Now you may wonder, wouldn’t men who do not commit or guard still have more offspring, albeit from various women? While women can mate with various men, they can only birth children from the same father per pregnancy (for the most part), which means that one opportunity to mate with someone does not guarantee paternity for the man. Think of the popular TV show Paternity Court, where if a woman has relationships with more than one man, the paternity of her child is not guaranteed for either of the partners involved. Hence, mating with multiple women does not necessarily guarantee having children, whereas for committed men who guard their women from other men, it is most likely that the children are theirs.
Of course, guarding a woman from other men does not necessarily give her an advantage to stay committed to the man, so responsibilities, care, and other foundations of relationships slowly evolved to become the modern institution of commitment, dating, and marriage that we see today (Schacht & Bell, 2017). From grandmothers to mate-guarding women to monogamy, this weird phenomenon evolved through an even weirder journey. Now, the next time you have a rather awkward conversation about commitment and exclusiveness with a romantic interest, don’t forget to thank your grandmother!
References
Coxworth, J. E., Kim, P. S., McQueen, J. S., & Hawkes, K. (2015a). Grandmothering life histories and human pair bonding. Proceedings of the National Academy of Sciences, 112(38), 11806–11811. https://doi.org/10.1073/pnas.1599993112
Edgar, B. (2016, March 1). Human monogamy has deep roots. Scientific American. https://www.scientificamerican.com/article/human-monogamy-has-deep-roots/
Lukas, D., & Clutton-Brock, T. H. (2013). The evolution of social monogamy in mammals. Science, 341(6145), 526–530. https://doi.org/10.1126/science.1238677
Male fertility: The best age to become a father, as per studies. (n.d.). The Times of India. Retrieved November 22, 2023, from https://timesofindia.indiatimes.com/life-style/parenting/getting-pregnant/male-fertility-the-best-age-to-become-a-father-as-per-studies/photostory/92132374.cms?from=mdr#
Schacht, R., & Bell, A. V. (2016). The evolution of monogamy in response to partner scarcity. Scientific Reports, 6(1), 32472. https://doi.org/10.1038/srep32472
Zimmer, C. (2013, August 2). Monogamy and human evolution. New York Times; The New York Times Company. https://www.nytimes.com/2013/08/02/science/monogamys-boost-to-human-evolution.html
Citation Style: APA