Macken Murphy is an evolutionary biologist at the University of Melbourne. Why do people cheat? Is it just the allure of novelty? Dissatisfaction in their current relationship? Fear of being left? Retaliation for their partner cheating? Macken’s brand new study gives so many fascinating answers to these questions. Expect to learn what the evolutionary drivers are behind men’s and women’s infidelity, what this new science says about the Dual Mating and Mate Switching hypotheses, the top 3 reasons for why men and women both cheat, whether cheating is heritable, if there is such a thing as one and done cheating, the most common behaviours of somebody who is being unfaithful and much more…
Facial Attractiveness: Signals and Preferences
Averageness: Faces that are mathematically average (the result of superimposing many faces) are consistently found attractive. This might be because they are easier for the brain to process, or because average traits represent the end result of historical sexual selection, where non-average features were selected against.
Symmetry: Facial symmetry is attractive and often correlates with other indicators of attractiveness. It is believed to signal robust underlying developmental qualities, demonstrating an individual's ability to withstand environmental insults, or the absence of severe injuries or heritable genetic disorders. While symmetry is attractive, its correlation with healthiness has mixed results in Western populations.
Facial Femininity (in women): Heterosexual men consistently find facial femininity in women very attractive.
Facial Masculinity (in men): Preferences for facial masculinity in men are mixed. Some studies suggest a slight preference for masculinity, others for femininity, and some show no effect. The latest reviews indicate a slight preference for facial femininity in men. While facial masculinity is associated with traits like fighting ability and testosterone levels, which can be impressive signals, it is not universally preferred above more feminine traits.
Eye Features: A dark ring around the iris (limbal ring) and clear white sclera are considered attractive, potentially acting as cues to health. Eye color preferences may be frequency-dependent, contributing to eye color diversity.
The Masculinity Trade-Off Hypothesis and Beards
The masculinity trade-off hypothesis suggests that highly masculine traits in men might be attractive for short-term mating but less appealing for long-term relationships, due to potential associations with risky behavior, aggression, or infidelity. However, this hypothesis has mixed results and is viewed with skepticism regarding its consistency across all contexts, particularly for short-term versus long-term mating.
Counter-intuitively, the male beard, a highly masculine ornament, is often preferred for a potential co-parent or "dad" rather than for short-term mating, which contradicts the simple masculinity trade-off hypothesis.
Research on beard preferences is complex, with studies equally divided on whether women prefer clean-shaven or bushy beards. However, heavy stubble consistently emerges as the most preferred facial hair style, as it signals the ability to grow a beard (masculinity) combined with regular maintenance (refinement, attentiveness, and available time/resources).
Body Shape and Environmental Influence (Women)
BMI and Environmental Security Hypothesis: Men's preferences for women's body mass index (BMI) are malleable and influenced by the socio-ecological context. In Western/industrialised societies, lower BMIs are generally preferred. However, in more traditional or resource-scarce environments, women with more body fat are often considered sexier, with BMIs up to 38 being viewed as attractive in some cultures (e.g., South African Zulu). This is explained by the environmental security hypothesis, where heavier women signal their ability to acquire calories, survive famine, and maintain fertility during scarcity. Evidence for this includes trends in media (Playboy models heavier during economic downturns) and even individual hunger levels (men prefer heavier mates before dinner than after).
Women's bodies naturally display conspicuous fat deposits on breasts, buttocks, and hips, which function as sexual signals.
Waist-to-Hip Ratio: While a 0.68 waist-to-hip ratio is often cited as a universal preference in evolutionary psychology, this may be a Westernized perspective. This ratio signals nulliparity (not having had children) and fertility, as it is harder to maintain after childbirth or with age. There is suggestive evidence that in environments where women engage in more physical labor, a more "masculine" figure (potentially with wider hips) might be preferred, as extremely wide hips can impede physical activity. Curvy figures with heavier BMIs are generally found more attractive than non-curvy ones.
Body Shape and Signaling (Men)
Muscularity: Muscular men tend to have higher mating success. Women often find men who are more muscular than average, but not excessively so (i.e., not "stage-ready bodybuilders"), more attractive.
Intimidation: In some contexts, a man's perceived "intimidation factor" can be a stronger predictor of mating success (number of mates) than his perceived hotness, potentially by deterring male competitors.
Height Preferences
For Men (by women): Women prefer men to be very tall, but not "too very tall." Attractiveness increases significantly from very short heights up to around 6'1", with diminishing returns for each additional inch thereafter, tapering off around 6'3" to 6'5". Heights above 6'6" might be less optimal but still generally preferred over being 5'10". Women seek a man who is taller than average, rather than simply taller than themselves.
For Women (by men): Men generally prefer women who are about average height or moderately shorter than themselves.
Hair Colour and Age Signaling
For Women (by men): Men tend to prefer relatively lighter hair colors in women. This is theorized to signal youth and nulliparity, as hair naturally darkens with age and potentially during pregnancy.
For Men (by women): Women often show a preference for somewhat darker hair, aligning with the "tall, dark, and handsome" stereotype.
Tattoos: Trade-offs in Signaling
Men with Tattoos (by women): Women perceive tattooed men as healthier, more masculine, and more dominant. However, studies suggest women generally do not find tattoos more attractive, and may view them as a signal of a less suitable long-term partner (e.g., less likely to be a good dad or husband), which is consistent with the masculinity trade-off idea.
Women with Tattoos (by men): While men don't necessarily find tattooed women more attractive, studies show that women with tattoos are approached more frequently by men. This is thought to be because tattoos can signal higher sociosexuality, a greater openness to risk-taking, or adventurousness, making tattooed women seem more approachable for a date.
Age Gaps in Relationships
Men's Preferences: As men age, they tend to desire increasingly wider age gaps, preferring younger women.
Women's Preferences: In societies where women have greater freedom and financial independence, they tend to choose men who are only slightly older (2-4 years), and this age gap preference is narrowing. This preference balances direct benefits (e.g., older men potentially having more resources or status) with indirect benefits (e.g., maintaining good sperm quality, as signals of genetic quality decline with age).
Mate Value, Signaling, and Effort
Beauty as a Shortcut Signal: Physical beauty functions as a shortcut signal for more fundamental underlying qualities that are important in a mate, such as health, conscientiousness, and reliability.
Signaling Effort: A person's appearance (e.g., well-styled hair, groomed stubble, carefully applied makeup, chosen outfit) signals effort, conscientiousness, reliability, and the availability of excess time and resources, which can indicate a better partner.
The "Goldilocks Zone": For many attractive traits, there exists a "Goldilocks zone" where moderate levels are most appealing. Extremes (e.g., excessive muscularity or makeup) can signal insecurity or trying too hard, potentially reducing attractiveness.
Effort in Attractiveness: Women globally spend significantly more time (approximately half an hour more per day) on enhancing their physical attractiveness compared to men, including time on grooming, fashion, and fitness. This suggests that much of women's perceived mate value is already the result of substantial effort, potentially limiting the "runway" for further improvement.
Stated vs. Revealed Preferences in Mating
There's often a divergence between what people *say* they want in a mate (stated preferences) and what they *actually do* (revealed preferences). While people often state that personality traits (e.g., honesty, kindness) are most important, studies like speed dating show that physical attractiveness often dominates initial choices.
The influence of physical attractiveness diminishes over time: if a couple knew each other for 9 months or more before dating, physical attractiveness is not a significant predictor of their decision to partner, suggesting personality and accumulated information become more important.
An understanding of human mating requires considering both stated preferences (what people want) and revealed preferences (what they do), along with the constraints and opportunities of their environment. For example, men may state they don't care about a woman's education, but often end up with educated women due to exposure and opportunity in their social circles.
Sex Differences in Mating Selectivity and Attractiveness
Women's Selectivity: Women are generally more selective in their mating choices than men, a pattern observed across most animal species. Men tend to be attracted to a broader range of women, whereas women are attracted to a smaller subset of men.
Comparative Attractiveness: If asked to rate attractiveness, both men and women tend to agree that women are, on average, hotter than men.
Compromise on Looks: Women appear more willing to compromise on physical attractiveness standards in a mate compared to men.
Sociosexuality and Relationship Outcomes
Higher levels of sociosexuality (past promiscuity or "body count") are associated with negative outcomes in long-term relationships for both men and women. The "optimal" number of past partners for women is around three, and "a few to several" for both sexes is generally perceived as desirable, with very low or very high numbers being less preferred.
A double standard exists where male promiscuity is often not viewed with the same societal negativity as female promiscuity, despite similar data on negative relationship outcomes for both sexes.
Malleability of Preferences and Cultural Context
Human mating preferences, including women's preference for socioeconomically successful (hypergamous) partners, are considered phenotypically plastic and can change over time. European trends, for example, show women becoming more willing to date hypogamously (partners with less wealth or education).
Women who intend to be the primary breadwinner in a relationship may prioritize "good dad qualities" and sexiness in a mate over their partner's income.
Cultural and socio-ecological factors heavily mediate attractiveness. For instance, preferences for skin tone (tanned vs. lighter) can vary depending on what that trait signals about social status or lifestyle in a specific culture.
Behavioral Ecology vs. Evolutionary Psychology
Evolutionary Psychology, historically rooted in cognitive psychology and evolutionary biology, often uses questionnaires to understand "stated preferences" and emphasizes shared human nature. It is considered necessary but often insufficient for fully understanding complex human behaviors.
Behavioral Ecology applies the rigorous methods used to study animal behavior to humans. It focuses on "revealed preferences" (what people actually do) within specific cultural and socio-ecological contexts. This approach is more flexible and often yields greater insights into how environment and culture shape mating behaviors.
A comprehensive understanding of human mating behavior requires integrating insights from both fields, considering both what people say and what they do, alongside their environmental and cultural influences.