Monogamy is so deeply embedded in our understanding of romantic relationships that most of us encounter it as the default rather than a choice. We date, fall in love, commit, and, somewhere along the way, sexual and romantic exclusivity become part of the deal. But where did that deal come from? In this episode, we take the conversation about infidelity from Episode 009 one step further and ask a bigger question: is monogamy actually natural for humans, and does it matter if it is? We explore evolutionary theories of romantic love, pair bonding, paternal care, and oxytocin, while remaining appropriately suspicious of research that begins with heteronormative assumptions and then works backwards to explain why it exists.
We distinguish social monogamy from sexual monogamy and wonder whether the benefits associated with long-term pair bonds necessarily require sexual exclusivity. We also get into Esther Perel’s ideas about mystery, distance, and desire in long-term relationships. Andrea agrees that relationships can become stagnant when partners stop allowing one another to change, but questions whether the answer is becoming more elusive. Creating distance may generate anxiety and pursuit, but is that actually desire? Instead, she offers another possibility: perhaps staying interested in a long-term partner has less to do with remaining mysterious and more to do with recognising that the person beside you is still evolving. Being deeply known does not have to mean becoming entirely predictable.
We also talk about the enormous range of ways humans structure relationships: monogamy, polyamory, sexual non-monogamy, polyfidelity, and plenty of arrangements that do not fit neatly into any category. Andrea shares her own evolution from struggling with being someone’s “secondary” in her twenties to eventually choosing polyamory for herself, not because she needs multiple partners, but because she wants room for whatever is real in her life to be real. That leads us to optionality, and the strange expectation that we should be able to decide in advance not only what we will do twenty years from now, but what we will feel.
Along the way, we discuss the existential terror of “one vagina for the rest of my life,” the questionable methodology of evolutionary psychology, and a mysterious culture in which researchers apparently found no evidence of romantic love and then inexplicably failed to tell us which one it was. We do not arrive at a verdict on whether monogamy is natural, nor do we decide that monogamy is good, bad, evolved, outdated, or doomed. We land somewhere more useful: do you know why you are doing what you are doing? Relationships change because people change. Whatever structure we choose, choose it with our eyes open, talk about it with the person or people we love, and keep updating the agreements as we update ourselves.
Questions to Take Home
Did you actively choose your relationship structure, or did you inherit it? What parts of monogamy, non-monogamy, marriage, or partnership have you consciously chosen, and what parts have you accepted because they seemed like the default?
What are you asking your current self to promise on behalf of your future self? Are there agreements in your relationship that would benefit from being discussed as ongoing choices rather than permanent assumptions?
Does being deeply known by your partner make you feel less desirable, or more free to keep evolving? Where is there still room for surprise, curiosity, and change between you?
A Note From the Lab
This episode is not an argument for or against monogamy. There are many ways to build a loving, sexually fulfilling, committed relationship, and no structure guarantees security, desire, fidelity, or longevity.
What interests us is the difference between defaulting into a relationship structure and choosing one. Monogamy can be a choice. Non-monogamy can be a choice. Those choices can also change.
As Andrea says, you do not have to pick a way that somebody else made up. And as Caroline keeps returning throughout the conversation, whatever you choose, keep asking why you are choosing it, whether it is still working, and whether the agreements you made in the past still fit the people you have become.
Research & Resources
Romantic Love, Pair Bonding, and Evolution
Garth J. O. Fletcher, Jeffry A. Simpson, Lorne Campbell, and Nickola C. Overall, “Pair-Bonding, Romantic Love, and Evolution: The Curious Case of Homo sapiens,” Perspectives on Psychological Science 10, no. 1 (2015): 20–36.
A review of research on romantic love, pair bonding, monogamy, alloparenting, and human evolution. Fletcher and colleagues examine the theory that romantic love functions as a commitment mechanism supporting long-term pair bonds, while also considering challenges including infidelity, divorce, polygyny, and arranged marriage. This is the primary article Andrea brings into the episode.
William R. Jankowiak and Edward F. Fischer, “A Cross-Cultural Perspective on Romantic Love,” Ethnology 31, no. 2 (1992): 149–155.
A cross-cultural analysis of romantic love using ethnographic evidence from 166 societies. This is the study behind our favourite unanswered question of the episode: if researchers found evidence of romantic love across almost all of the cultures examined, what was happening in the one culture in which its absence was specifically reported?
Oxytocin, Attraction, and Pair Bonding
Dirk Scheele, Nadine Striepens, Onur Güntürkün, Sandra Deutschländer, Wolfgang Maier, Keith M. Kendrick, and René Hurlemann, “Oxytocin Modulates Social Distance between Males and Females,” The Journal of Neuroscience 32, no. 46 (2012): 16074–16079.
In a randomised, placebo-controlled experiment, heterosexual men in monogamous relationships who received intranasal oxytocin maintained greater physical distance from an unfamiliar attractive woman than partnered men receiving a placebo. The effect was not found among single men. The study is interesting evidence for a possible role of oxytocin in maintaining established pair bonds, although its male-only, heterosexual sample limits how broadly the findings can be interpreted.
Dirk Scheele, Andrea Wille, Keith M. Kendrick, Birgit Stoffel-Wagner, Benjamin Becker, Onur Güntürkün, Wolfgang Maier, and René Hurlemann, “Oxytocin Enhances Brain Reward System Responses in Men Viewing the Face of Their Female Partner,” Proceedings of the National Academy of Sciences 110, no. 50 (2013): 20308–20313.
Using double-blind, placebo-controlled experiments with heterosexual partnered men, the researchers found that intranasal oxytocin increased reward-related neural responses when participants viewed images of their female partners. Together with Scheele and colleagues’ earlier work, the research contributes to theories about oxytocin’s role in partner-specific attachment and human pair bonding.
Human Sexuality, Fidelity, and Relationship Structure
Justin R. Garcia, The Intimate Animal: The Science of Love, Fidelity and Connection (London: Penguin Life, 2026).
Evolutionary biologist and Kinsey Institute Executive Director Justin Garcia examines love, sex, fidelity, pair bonding, and the tension between humans’ capacities for long-term attachment and sexual novelty. His work provides useful context for our discussion of social and sexual monogamy and the difficulty of reducing human relationships to a single biological or cultural explanation.
Desire, Mystery, and Long-Term Relationships
Esther Perel, Mating in Captivity: Reconciling the Erotic and the Domestic (New York: HarperCollins, 2006).
Perel explores the tension between security and eroticism in long-term relationships and argues that desire often benefits from separateness, novelty, and space between partners. Andrea agrees with much of the problem Perel identifies but diverges on the solution. Rather than cultivating elusiveness, she argues for continued evolution: allowing ourselves and our partners to remain changing people who can still surprise one another without sacrificing the intimacy of being deeply known.
