The Pros and Cons of Monogamy (After Reading Sex at Dawn)

I recently read Sex at Dawn by Christopher Ryan and Cacilda Jethá. It's a book I'd been aware of and avoided reading, partly because I suspected it would complicate a set of beliefs I was comfortable with.

It did. And I'm glad I read it anyway.

I'm nine years into a monogamous marriage that I'm genuinely happy in. Brittney and I are not exploring non-monogamy, and I have no interest in doing so. But I found the book's central arguments compelling enough that I can't dismiss them and honest engagement with ideas that challenge your position is more valuable than the comfort of never encountering them.

Here's my honest reckoning with the pros and cons of monogamy, informed by a book that mostly argues against it.

A couple sits closely on a bench, while one partner discreetly holds hands with another person behind their backs.

What Sex at Dawn Actually Argues

Ryan and Jethá's core claim is that human beings did not evolve as a monogamous species, and that the standard narrative — that pair bonding is our natural state and that agriculture merely formalized what was already biologically true — has the causation backwards.

Their argument draws on several lines of evidence. Comparative primatology: our closest relatives, chimpanzees and especially bonobos, are highly promiscuous and use sexuality for social bonding rather than exclusively for reproduction. Anatomical evidence: human testicle size relative to body mass, the shape of the penis, female copulatory vocalization, and extended female receptivity all suggest a mating system involving sperm competition rather than exclusive pairing. Anthropological evidence from remaining foraging societies: many practice forms of partible paternity or non-exclusive sexuality that would be inexplicable if monogamy were our species default.

Their conclusion: monogamy is a cultural institution that emerged with agriculture, private property, and the need to establish paternity for inheritance — roughly ten thousand years ago, which is a blink in evolutionary terms. The difficulty many people experience sustaining monogamous desire over decades isn't a personal failure. It's friction between a cultural structure and a biological inheritance that didn't evolve for it.

The Case Against Monogamy

Taking the book's arguments seriously, here's the honest case:

Desire habituation is real and biological. The Coolidge effect — the well-documented phenomenon in which sexual interest is renewed by novel partners — has been demonstrated across many mammalian species including humans. Familiarity reliably reduces sexual response. This isn't a character flaw or a relationship failure. It's a robust biological pattern that monogamy asks people to override indefinitely.

The expectation load is historically unprecedented. As I wrote drawing on Esther Perel's work, we ask a single person to be our best friend, primary emotional support, co-parent, financial partner, intellectual equal, and passionate lover — a set of demands that no previous era placed on one relationship. Monogamy in this configuration is being asked to carry more than monogamy has historically been asked to carry.

Infidelity rates suggest structural strain. Estimates vary widely, but studies consistently find infidelity rates in the 20-40% range for married individuals. Whatever one's moral view of that, a structure that a significant minority of participants violate is a structure under genuine tension.

Sexual boredom is a leading cause of relationship dissolution. Not the only one, but a persistent and significant contributor — which is at minimum consistent with the argument that indefinite exclusive desire is difficult to sustain.

The Case For Monogamy

Here's where I land, and where I think the book underweights some genuine goods.

Depth is a different value than novelty, and it's not lesser. Sex at Dawn is strongest on the argument that novelty produces charge. It's weakest on what long-duration exclusive partnership produces that nothing else can. Nine years in, Brittney knows me in a way that no new partner could — not because new partners lack capacity, but because the knowing itself requires time. The intimacy of being genuinely known by someone who has witnessed you across years, through difficulty, in your worst moments and your best, is a category of experience that novelty structurally cannot provide.

The security enables the exploration. This is the point I think the book most misses. The erotic exploration Brittney and I have been doing over the past several years — everything I write about on this blog — has been possible because of the security of an exclusive committed partnership, not despite it. The vulnerability required to explore genuinely requires enough safety to risk it. Monogamy, done well, produces that safety.

Depletion is real too. Novelty produces charge, but it also has costs the book undercounts: the emotional labor of managing multiple relationships, the jealousy management, the time and attention division, the instability that some people thrive in and others find corrosive. Non-monogamy isn't free of difficulty; it trades one set of difficulties for another.

The difficulty is workable. This is the crux. Yes, sustaining desire over decades is genuinely difficult. But "difficult" and "impossible" are different claims. The entire project of this blog is documenting that the difficulty is workable — that couples who bring intentionality, presence, honest communication, and genuine practice to their intimate lives can sustain something alive over long duration. Ryan and Jethá are right that it doesn't happen automatically. They underweight how much it responds to deliberate effort.

Where I Actually Land

I'm monogamous by choice and by genuine preference, and I'm more clear-eyed about it after reading the book than I was before.

What Sex at Dawn usefully dismantles is the naive version of monogamy — the assumption that exclusive desire should sustain itself effortlessly, that difficulty means something is wrong, that a wandering eye is evidence of a defective relationship or a defective person. That version of monogamy sets people up for shame and disappointment, and it deserves dismantling.

What replaces it, for me, is a version I'd call chosen monogamy: an arrangement I've deliberately selected, understanding that it runs against certain biological currents, and that therefore requires ongoing intentional investment rather than passive maintenance.

That framing has made me a better partner. It removed the expectation that desire should be automatic, which removed the shame when it wasn't, which made room for the actual work of tending it deliberately.

If you're in a monogamous relationship and struggling with desire, the most useful thing Sex at Dawn offers isn't permission to open your relationship. It's the reframe that the struggle is structural rather than personal — and structural problems respond to structural solutions.

Read it. Let it complicate things. Then choose deliberately what you want to build.

Ready to go deeper?

If this resonates, there are two ways to take the next step with Coelle.

Download the Coelle app — Guided audio intimacy sessions designed for couples who are ready to stop performing and start arriving. The deliberate investment that chosen monogamy requires, made practical. Download Coelle here.

Work with me directly — I offer one-on-one sex and intimacy coaching for individuals and couples, drawing on my background in sport psychology and years of personal somatic work. Learn more about coaching here.