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Relationship Scientist REVEALS 3 CLEAR SIGNS He'll CHEAT (Don’t Miss THIS RED FLAG!) | Macken Murphy

Today we welcome the inspiring Macken Murphy. Macken isn't just a behavior scientist; he's a master at decoding the little things we do and say that reveal a lot about our relationships and what we're really looking for in love and life.

Macken MurphyguestLewis Howeshost

Mar 13, 20241h 28mWatch on YouTube

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Chapter summaries

Macken Murphy’s infidelity research, narcissism link, and why cheating can be traumatic
Macken Murphy opens with key claims from his research interests: infidelity has predictors (including narcissism) and being cheated on can produce PTSD-like symptoms. Lewis Howes frames Macken as a behavior scientist who studies human mating behavior and relationship dynamics, setting up the conversation’s focus on cheating, jealousy, and attraction.
- •Macken says narcissism is associated with infidelity, including “sexual narcissism.”
- •Macken says some psychologists use the term “post-infidelity stress disorder” for PTSD-like symptoms after being cheated on.
- •Lewis positions the episode around understanding cheating, jealousy, insecurity, and attraction through research.
- •Lewis asks what research stands out most about love, relationships, and intimacy.
- •Lewis tees up the question about “three clear signs” a committed man may cheat.
Do men cheat more than women? How research approaches the question
Macken explains how infidelity is studied (including the term “extra pair copulation”) and argues that, in general, men cheat more than women based on common research measures. He also acknowledges debate, possible variation across groups, and limitations of self-report.
- •Macken frames infidelity as “extra pair copulation” and discusses humans as a “serially socially monogamous” species.
- •Macken says men tend to report cheating more, while heterosexual women report being cheated on more.
- •He notes concerns about self-report and adds that research on lying suggests men may be more duplicitous.
- •Macken discusses evidence from “mate poaching” reports and differential success rates.
- •He emphasizes being open to new evidence and not being emotionally committed to the conclusion.
Why people cheat: evolutionary benefits, mate-switching, and other functions
Macken argues cheating can serve different functions rather than having one single cause. He lays out a key evolutionary rationale for why male mammals might benefit more from multiple mating, while also describing relationship-driven motives like mate-switching and keeping security while exploring alternatives.
- •Macken separates describing infidelity as “natural/evolved” from calling it good or inevitable.
- •He explains a theoretical reason men might cheat more: male mammals can increase offspring via multiple partners.
- •Lewis pushes back with modern social realities; Macken agrees it’s not socially accepted and not harmonious.
- •Macken lists other motives beyond sexual variety, including mate-switching for both men and women.
- •He quotes a comparison about not quitting a job before lining up another one to explain why people don’t just break up first.
Motives for women to cheat: revenge, resources, and “mixing” partner benefits
Macken answers why women cheat by describing multiple strategies that can overlap with men’s motives. He highlights revenge as one possible driver, and then focuses on how socio-ecological conditions can shape infidelity motivations, including seeking multiple investors and pairing different kinds of benefits across partners.
- •Macken says women and men can both cheat to mate-switch and for revenge; he notes evidence women may be more likely to cite revenge.
- •He describes very high infidelity rates in the Himba of Namibia, including women’s infidelity.
- •Macken says research there suggests women cheat primarily to obtain multiple “investors” (resources/support).
- •He gives a Western-style example resembling having multiple provisioning partners (including a “sugar daddy”-type relationship).
- •He describes a low-frequency strategy of combining indirect/conceptive benefits from one partner with direct investment from another.
Paternity-rate myths and how culture changes what infidelity means
Lewis and Macken address popular claims about high rates of “you are not the father,” with Macken arguing those numbers often come from biased samples. They contrast Western reactions to nonpaternity with the Himba context, where relationship meaning and social status can differ dramatically.
- •Macken criticizes the claim that nonpaternity is ~30%, saying it reflects paternity-clinic sampling bias.
- •He says general-population Western studies are much lower, and notes some groups can be far higher.
- •Macken describes the Himba context as culturally distinct, with high nonpaternity and different relationship consequences.
- •Lewis suggests communal/tribe child-rearing dynamics; Macken agrees it’s related to multiple investors and status dynamics.
- •Macken cautions that a specialist would be better for deep detail on that specific setting.
Monogamy vs. polyamory: what Macken is and isn’t claiming about outcomes
Lewis asks whether polyamory or monogamy produces more harmony and stability. Macken distinguishes infidelity from rule-based nonmonogamy, then offers a tentative societal argument that monogamy can bring broad social benefits while acknowledging selection effects and individual differences.
- •Macken says formal polyamory isn’t infidelity if it follows relationship rules.
- •He declines to claim expertise on polyamory research, emphasizing academic humility.
- •He argues monogamy appears linked to societal benefits like stability and reduced violence, describing excluded single men as a risk factor for social trouble.
- •Macken uses analogies (football, skydiving) to explain self-selection and why group comparisons can mislead.
- •He concludes polyamory may suit some individuals while still suggesting monogamy may be better socially, tentatively.
Three red flags for cheating risk: family history and sociosexuality (plus how “body count” fits)
Lewis presses for concrete signs of cheating risk. Macken reframes them as risk factors, emphasizing family history and a person’s sociosexuality (comfort with uncommitted sex), and then addresses how “body count” can be a rough proxy depending on context.
- •Macken says there are no perfectly “clear signs,” but red flags exist as risk factors.
- •He names family history: infidelity can run in families and may be partly genetic and partly social.
- •He names sociosexuality as another risk factor: enjoyment of uncommitted mating predicts higher likelihood of infidelity.
- •Macken says these factors apply to women as well as men, warning against gender-war framing.
- •On “body count,” Macken says there’s likely an association with infidelity risk, but context matters (same number can describe very different life patterns).
Promiscuity stigma, “ideal body count,” and who actually cares
The conversation turns to why promiscuity is judged differently for men and women. Macken argues that negative associations between promiscuity and relationship outcomes often show up for both genders in the studies he’s aware of, and he discusses survey findings on preferences for a moderate sexual history.
- •Macken says many studies finding negative links between promiscuity and relationship outcomes show similar patterns in men and women.
- •He says he doesn’t know the full explanation for why stigma is harsher toward women, but suggests power dynamics may be involved.
- •Macken notes survey work indicating both men and women care about “ideal body count.”
- •He describes the “ideal” as a moderate number (not zero, not very high), and notes people tend to dislike both inexperience and “too much experience.”
- •He warns against treating these findings as a reason to “optimize” a number, noting it could encourage dishonesty.
Jealousy: evolved emotion, when it feels ‘sexy,’ and Lewis’s personal shift away from it
Lewis asks whether jealousy signals love or toxicity. Macken describes jealousy as an evolved emotion tied to threats to fidelity and investment, while Lewis shares his lived experience that jealousy caused stress and didn’t help his relationships, and how that changed in his mid-30s.
- •Macken calls jealousy a naturally evolved human emotion related to threats to partner fidelity.
- •He explains different evolutionary logic: men’s jealousy tied to paternity concerns; women’s jealousy tied to losing investment.
- •Lewis describes decades of jealousy as painful, anxiety-producing, and behavior-warping in his relationships.
- •Lewis explains a mindset shift: if someone doesn’t want to be with him, jealousy is pointless and moving on sooner is better.
- •Both discuss “playful protectiveness” versus controlling behaviors like surveillance and constant check-ins.
Signs of being in love—and whether relationships can survive infidelity
Macken describes romantic love through Helen Fisher’s framing and highlights obsessive thinking as a key proxy for acute romantic love. The conversation then turns to whether couples can recover from cheating, the predictive value of past cheating, and how infidelity risk differs depending on life context.
- •Macken says a key proxy for being ‘in love’ is obsessive thinking and attributing special meaning to a partner’s traits.
- •He describes love as three systems: lust, acute romantic love, and attachment, with the “honeymoon” phase typically fading over time.
- •Lewis asks if relationships can work after cheating; Macken says some couples do survive infidelity.
- •Macken references longitudinal research suggesting people who cheated previously are more likely to cheat again, while emphasizing it’s not deterministic.
- •He notes context matters (e.g., long relationships and families complicate decisions versus younger relationships).
After cheating trauma: reassurance seeking, PISD, and why some people get cheated on repeatedly
Lewis asks how to approach dating someone who has been cheated on and may struggle with trust. Macken describes reassurance seeking and rumination as common, frames infidelity as potentially traumatic, and then explores an additional finding: people previously cheated on may be at higher risk of being cheated on again, potentially due to partner selection and relationship dynamics.
- •Macken identifies reassurance seeking as a common behavior among people who’ve been cheated on.
- •He says PTSD-like symptoms are common enough that some use the term “post-infidelity stress disorder.”
- •Macken criticizes online narratives that treat men’s cheating as acceptable while dismissing women’s pain, calling it careless.
- •He discusses evidence (from a single study, cautiously) that being cheated on previously may predict being cheated on again.
- •He offers possible mechanisms: attraction to traits associated with infidelity (e.g., narcissism), prioritizing physical attractiveness, and dynamics where repeated false accusations can push someone toward actual cheating.
Gen Z, the “mating crisis,” animal analogies, and building better relationships (including attractiveness)
Lewis asks whether Gen Z cheats more; Macken says he sees no evidence and suggests young people may be engaging in less risky sexual behavior overall. He then discusses the idea of a “mating crisis” cautiously, explains why infidelity isn’t simply pathological using animal examples, and transitions into research-backed relationship behaviors like compliments, affection, and maintaining attractiveness.
- •Macken says he sees no evidence Gen Z cheats more; he suggests young people may be engaging in less risky sexual behavior generally.
- •He cautiously references the idea of a “mating crisis,” including theories about risk reduction and more conservative social behaviors in some ways.
- •Macken discusses infidelity across socially monogamous species and gives gibbons as an example of monogamy with notable extra-pair copulation rates.
- •He argues that repeated cheating experiences may call for reflection on partner selection (“picking”) and creating a relationship atmosphere people want to stay in.
- •Macken highlights simple behaviors linked to relationship success: more sex, compliments, flirting, and non-escalative touch like cuddling, plus not neglecting physical self-care and attractiveness over time.
Putting the science aside, Couply app mission, and closing ‘Three Truths’ + definition of greatness
Macken explains he doesn’t constantly “run data” in his head during relationships, using an “eating an apple” analogy to describe simply being present. Lewis and Macken discuss Couply’s goal of helping couples maintain relationships, then close with Macken’s ‘Three Truths’ and his admiration for people who succeed at home and family life.
- •Macken says he mostly puts analysis aside in real relationships and follows his emotions, comparing it to enjoying an apple without overthinking evolution.
- •Lewis and Macken discuss Couply as an app intended to help people stay and grow in relationships, not just find new ones.
- •Macken describes Couply features like quizzes, courses, and bringing data-informed relationship insights into a smartphone tool.
- •In the “Three Truths,” Macken emphasizes living by values, prioritizing “obituary virtues” over “resume virtues,” and being careful about partner choice and relationship skill-building.
- •Macken defines greatness as real success “in the home,” admiring people who have family life truly sorted.

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