Mate Choice Copying in Humans: a Systematic Review and Meta-Analysis

Mate assessment based on physical characteristics: a review and reflection

Mate choice, and sex differences in romantic behaviours, represented one of the first major applications of evolutionary biology to human behaviour. This paper reviews Darwinian approaches to heterosexual mate assessment based on physical characteristics, placing the literature in its historical context (1871-1979), before turning (predominantly) to psychological research on attractiveness judgements based on physical characteristics. Attractiveness is consistently inferred across multiple modalities, with biological theories explaining why we differentiate certain individuals, on average, from others. Simultaneously, it is a judgement that varies systematically in light of our own traits, environment, and experiences. Over 30 years of research has generated robust effects alongside reasons to be humble in our lack of understanding of the precise physiological mechanisms involved in mate assessment. This review concludes with three questions to focus attention in further research, and proposes that our romantic preferences still provide a critical window into the evolution of human sexuality.

When Your Partner is Being Flirted With: The Impact of Unsolicited Attention on Perceived Partner Desirability and Mate Retention Efforts

When searching for a partner, people often rely on social cues to determine partners' suitability, finding those who attract attention from others particularly appealing. While people continue to evaluate their partners beyond relationship initiation, existing research has predominantly concentrated on the effects of observing others' choices during the stage of partner selection, neglecting to consider whether viewing others' attention toward current partners yields similar effects or instead elicits defensive devaluation. In three experiments, we exposed Israeli participants to situations where their partners received unsolicited flirtatious advances, utilizing visualization, virtual reality, and recall techniques. Participants then rated their desire for their partner and mate retention efforts. Results indicated that attention to partners led to decreased desire for them, subsequently predicting reduced relationship investment. These findings suggest that witnessing current partners receiving attention holds a different meaning than observing potential partners in a similar situation, making salient the risk of losing the partner.

Is the Grass Really Greener? The Influence of Gender Identity and Sexual Orientation on Mate Copying Behaviors

Mate copying is a sexual strategy whereby individuals attend to socially available information about their prospective mate. This allows for more accurate decision making in regard to mating. This phenomenon was originally demonstrated among nonhumans, but there is an increasing weight of evidence suggesting that humans also engage in mate copying. Research typically focuses on heterosexual cisgender women, with no previous studies having looked at those identifying outside of the traditional gender binary. The current study aimed to address this gap by examining the impact of gender identity and sexual orientation on the propensity to engage in mate copying. Participants (N = 831) completed an online survey providing desirability ratings for photographs alone (T₁) and then rated the same photographs after receiving social information about the relationship status and previous relationship history of the pictured individual (T₂). It was found that both gender identity (F(4, 713) = 3.94, η_p² = .02) and sexual orientation (F(4, 713) = 4.40, η_p² = .02) influenced an individual's overall propensity to mate copy, and that desirability patterns for individuals were very different depending on these variables. It was concluded that while mate copying certainly is evident among humans, the phenomenon is extremely nuanced and sensitive.

Exploring the Influence of Race in Mate Copying Using Former Partner Evaluations

Human mate choice is a complex, nuanced process that incorporates factors including physical attractiveness, race, culture, and social values. Choosing the wrong partner can be a risky and costly affair; hence, mate choosers may copy the choices of others to inform their own decisions about the mate quality of a potential partner. This phenomenon is known as mate copying (MC). Consistent with previous research methods, the current study presented a sample of 461 Australian women with photographic stimuli of target men of one of three races paired with a description of a former female partner evaluating the target man either positively or negatively. Racial similarity between participants and the target man was statistically controlled for. As hypothesised, positive evaluations elicited MC whereas negative evaluations elicited mate avoidance. Racial similarity was also shown to influence measures of desirability and MC propensity. Results were discussed within the context of existing human MC literature, with particular emphasis on exploring how new factors affect the expression of MC intent within the Australian female demographic. Recommendations for further research based on these outcomes were also made.

Call Me Daddy: How Long-term Desirability Is Influenced by Intention for Fatherhood

One of the most important decisions an individual can make involves investing in a mating relationship. For women, the process of mate selection can be time-intensive and fraught with costs and dangers. However, these risks can be minimised by attending to relevant social information and modelling the mate choices of others. The propensity of imitating another’s mate choices is referred to as mate copying. Most research has focused on this behaviour in non-humans, but evidence of its existence in humans is emerging. The current study sought to determine conditions that modify a man’s desirability. The present study examined 267 women’s evaluations of men depicted in silhouetted images who varied in terms of their intentions for fatherhood and relationship history. Results showed that a man’s desirability as a long term mate was enhanced if he wished to become a father, and/or if he had a previous relationship experience, indicating he had been formerly chosen or preferred. These findings add to the existing body of knowledge on mate copying and attention to social information by demonstrating how women incorporate social learning and innate evolutionary predispositions to facilitate decision-making and behaviour relating to mate selection.

Mate Choice, Sex Roles and Sexual Cognition: Neuronal Prerequisites Supporting Cognitive Mate Choice

Across taxa, mate choice is a highly selective process involving both intra- and intersexual selection processes aiming to pass on one’s genes, making mate choice a pivotal tool of sexual selection. Individuals adapt mate choice behavior dynamically in response to environmental and social changes. These changes are perceived sensorily and integrated on a neuronal level, which ultimately leads to an adequate behavioral response. Along with perception and prior to an appropriate behavioral response, the choosing sex has (1) to recognize and discriminate between the prospective mates and (2) to be able to assess and compare their performance in order to make an informed decision. To do so, cognitive processes allow for the simultaneous processing of multiple information from the (in-) animate environment as well as from a variety of both sexual and social (but non-sexual) conspecific cues. Although many behavioral aspects of cognition on one side and of mate choice displays on the other are well understood, the interplay of neuronal mechanisms governing both determinants, i.e., governing cognitive mate choice have been described only vaguely. This review aimed to throw a spotlight on neuronal prerequisites, networks and processes supporting the interaction between mate choice, sex roles and sexual cognition, hence, supporting cognitive mate choice. How does neuronal activity differ between males and females regarding social cognition? Does sex or the respective sex role within the prevailing mating system mirror at a neuronal level? How does cognitive competence affect mate choice? Conversely, how does mate choice affect the cognitive abilities of both sexes? Benefitting from studies using different neuroanatomical techniques such as neuronal activity markers, differential coexpression or candidate gene analyses, modulatory effects of neurotransmitters and hormones, or imaging techniques such as fMRI, there is ample evidence pointing to a reflection of sex and the respective sex role at the neuronal level, at least in individual brain regions. Moreover, this review aims to summarize evidence for cognitive abilities influencing mate choice and vice versa. At the same time, new questions arise centering the complex relationship between neurobiology, cognition and mate choice, which we will perhaps be able to answer with new experimental techniques.

Trait/Financial Information of Potential Male Mate Eliminates Mate-Choice Copying by Women: Trade-Off Between Social Information and Personal Information in Mate Selection

Mate-choice copying occurs when people rely on the mate choices of others (social information) to inform their own mate decisions. The present study investigated women's strategic trade-off between such social learning and using the personal information of a potential mate. We conducted two experiments to investigate how mate-choice copying was affected by the personal information (e.g., trait/financial information, negative/positive valence of this information, and attractiveness) of a potential male mate in short-/long-term mate selection. The results demonstrated that when women had no trait/financial information other than photos of potential mates, they showed mate-choice copying, but when women obtained personality trait or financial situation information (no matter negative or positive) of a potential mate, their mate-choice copying disappeared; this effect was only observed for low-attractiveness and long-term potential partners. These results demonstrated human social learning strategies in mate selection through a trade-off between social information and personal information.

Making Choices in Discourse: New Alternative Masculinities Opposing the "Warrior's Rest"

Psychology research on men studies, attractiveness, and partner preferences has evolved from the influence of sociobiological perspectives to the role of interactions in shaping election toward sexual–affective relationships and desire toward different kinds of masculinities. However, there is a scientific gap in how language and communicative acts among women influence the kind of partner they feel attracted to and in the reproduction of relationship double standards, like the myth of the “warrior’s rest” where female attractiveness to “bad boys” is encouraged or supported. Some women imitate “the warrior” behavior of men by choosing dominant traditional masculinities (DTM) to have “fun” with and oppressed traditional masculinities (OTM) for “rest” after the “fun” with DTM—choosing an OTM for a stable relationship, but perhaps without passion, while also feeling attraction toward DTM, a response which perpetuates the chauvinist double standard that the feminist movement has condemned when men behave in this sexist way. Through conducting a qualitative study with communicative daily life stories, this article explores, on the one hand, how language and social interaction among women can lead to the reproduction of the DTM role by women and, on the other hand, also how new alternative masculinities (NAM) offer an alternative by explicitly rejecting, through the language of desire, to be the rest for the female warrior, the second fiddle to any woman. This has the potential to become a highly attractive alternative to DTM. Findings provide new knowledge through the analysis of communicative acts and masculinities evidencing the importance of language uses in the reproduction of the double standards in gender relations and to understand how and why these practices are maintained and which kind of language uses can contribute to preventing them. Implications for research and interventions on preventive socialization of gender violence are discussed.

The dissociable influence of social context on judgements of facial attractiveness and trustworthiness

The cheerleader effect occurs when the same face is rated to be more attractive when it is seen in a group compared to when seen alone. We investigated whether this phenomenon also occurs for trustworthiness judgements, and examined how these effects are influenced by the characteristics of the individual being evaluated and those of the group they are seen in. Across three experiments, we reliably replicated the cheerleader effect. Most faces became more attractive in a group. Yet, the size of the cheerleader effect that each face experienced was not related to its own attractiveness, nor to the attractiveness of the group or the group's digitally averaged face. We discuss the implications of our findings for the hierarchical encoding and contrast mechanisms that have previously been used to explain the cheerleader effect. Surprisingly, judgements of facial trustworthiness did not experience a 'cheerleader effect'. Instead, we found that untrustworthy faces became significantly more trustworthy in all groups, while there was no change for faces that were already trustworthy alone. Taken together, our results demonstrate that social context can have a dissociable influence on our first impressions, depending on the trait being evaluated.

Estimation in meta-analyses of response ratios

BACKGROUND

For outcomes that studies report as the means in the treatment and control groups, some medical applications and nearly half of meta-analyses in ecology express the effect as the ratio of means (RoM), also called the response ratio (RR), analyzed in the logarithmic scale as the log-response-ratio, LRR.

METHODS

In random-effects meta-analysis of LRR, with normal and lognormal data, we studied the performance of estimators of the between-study variance, τ², (measured by bias and coverage) in assessing heterogeneity of study-level effects, and also the performance of related estimators of the overall effect in the log scale, λ. We obtained additional empirical evidence from two examples.

RESULTS

The results of our extensive simulations showed several challenges in using LRR as an effect measure. Point estimators of τ² had considerable bias or were unreliable, and interval estimators of τ² seldom had the intended 95% coverage for small to moderate-sized samples (n<40). Results for estimating λ differed between lognormal and normal data.

CONCLUSIONS

For lognormal data, we can recommend only SSW, a weighted average in which a study's weight is proportional to its effective sample size, (when n≥40) and its companion interval (when n≥10). Normal data posed greater challenges. When the means were far enough from 0 (more than one standard deviation, 4 in our simulations), SSW was practically unbiased, and its companion interval was the only option.

A meta-analysis of factors influencing the strength of mate-choice copying in animals

Mate-choice copying is a form of social learning in which an individual’s choice of mate is influenced by the apparent choices of other individuals of the same sex and has been observed in more than 20 species across a broad taxonomic range. Though fitness benefits of copying have proven difficult to measure, theory suggests that copying should not be beneficial for all species or contexts. However, the factors influencing the evolution and expression of copying have proven difficult to resolve. We systematically searched the literature for studies of mate-choice copying in nonhuman animals and, then, performed a phylogenetically controlled meta-analysis to explore which factors influence the expression of copying across species. Across 58 published studies in 23 species, we find strong evidence that animals copy the mate choice of others. The strength of copying was significantly influenced by taxonomic group; however, sample size limitations mean it is difficult to draw firm conclusions regarding copying in mammals and arthropods. The strength of copying was also influenced by experimental design: copying was stronger when choosers were tested before and after witnessing a conspecific’s mate choice compared to when choosers with social information were compared to choosers without. Importantly, we did not detect any difference in the strength of copying between males and females or in relation to the rate of multiple mating. Our search also highlights that more empirical work is needed to investigate copying in a broader range of species, especially those with differing mating systems and levels of reproductive investment.

Factors that affect non-independent mate choice

Mate choice is generally regarded as an independent event, but a growing body of evidence indicates that it can be influenced by social information provided by conspecifics. This is known as non-independent mate choice. Individuals use information gathered by observing interactions between conspecifics to copy or not copy the mate choice of these conspecifics. In this review, we examine the factors that affect non-independent mate choice and mate choice copying and how it is influenced by social and environmental information that is available to the subject or focal individual. Specifically, we discuss how non-independent mate choice and whether individuals copy the choices of conspecifics can be influenced by factors such as habitat and differences in ecology, mating system and parental care. We focus on the social information provided to the focal animal, the model and the audience. Nearly all studies of non-independent mate choice and mate copying have focused on individuals in species that use visual cues as the source of social information. Nevertheless, we highlight studies that indicate that individuals in some species may use chemical cues and signals as sources of social information that may affect non-independent mate choice and mate copying.

Limited evidence of hierarchical encoding in the cheerleader effect

"The cheerleader effect" refers to the increase in attractiveness that an individual face experiences when seen in a group of other faces. It has been proposed that the cheerleader effect occurs because (a) the visual system rapidly summarises a group of faces into an ensemble representation, (b) which is hypothesised to be highly attractive because of its average facial characteristics, and (c) observers remember individual faces to be more alike the ensemble representation than they were, due to hierarchical structure of visual working memory. Across three experiments, we investigated whether the cheerleader effect is consistent with hierarchical encoding, by asking observers to give attractiveness ratings to the same target faces shown in groups and alone. Consistent with hierarchical encoding, the largest attractiveness increases of 1.5-2.0% occurred when target faces were presented in groups of faces that could be mentally summarised to create an ensemble representation with average facial characteristics. Surprisingly, smaller cheerleader effects still occurred in conditions that were incompatible with hierarchical encoding (i.e., groups with non-human images). Together, these results offer only limited evidence for the role of hierarchical encoding in the cheerleader effect, suggesting that alternative mechanisms must be explored in future research.

The Interplay Between Economic Status and Attractiveness, and the Importance of Attire in Mate Choice Judgments

Desirable characteristics of "opposite sex others," such as physical attractiveness and economic status, can influence how individuals are judged, and this is different for men and women. However, under various social contexts where cues of higher or lower economic status is suggested, sex differences in judgments related to mate choice have not been fully explored. In two studies, ratings of economic status and attractiveness were quantified for male and female targets that were presented under various social contexts. Study 1 assessed judgments (n = 1,359) of images of nine male and nine female targets in different sized groups containing only opposite-sex others (i.e., group size). While we found no significant effects of group size on male and female attractiveness, target female economic status increased when surrounded by two or more men. An ad hoc analysis controlling for the attire of the targets (business or casual) found that the association between target female economic status and group size occurred when females were in business attire. Study 2 investigates this effect further by presenting images of 12 males and 12 females, in higher and lower status attire (i.e., business and casual clothing) and measured judgments of attractiveness and economic status among women and men (n = 1,038). Consistent with the results of Study 1, female economic status was only affected when women were in business attire. However, female economic status decreased when in the presence of other men in business attire. There were no sex differences in judgments of economic status when judging stimuli in casual attire. Additionally, negative associations between attractiveness and economic status were found for males presented in casual attire. We discuss these results in the light of evolutionary sexual conflict theory by demonstrating how the asymmetrical importance of status between men and women can influence mate choice judgments.

Facial Adiposity, Attractiveness, and Health: A Review

The relationship between facial cues and perceptions of health and attractiveness in others plays an influential role in our social interactions and mating behaviors. Several facial cues have historically been investigated in this regard, with facial adiposity being the newest addition. Evidence is mounting that a robust link exists between facial adiposity and attractiveness, as well as perceived health. Facial adiposity has also been linked to various health outcomes such as cardiovascular disease, respiratory disease, blood pressure, immune function, diabetes, arthritis, oxidative stress, hormones, and mental health. Though recent advances in the analysis of facial morphology has led to significant strides in the description and quantification of facial cues, it is becoming increasingly clear that there is a great deal of nuance in the way that humans use and integrate facial cues to form coherent social or health judgments of others. This paper serves as a review of the current literature on the relationship between facial adiposity, attractiveness, and health. A key component in utilizing facial adiposity as a cue to health and attractiveness perceptions is that people need to be able to estimate body mass from facial cues. To estimate the strength of the relationship between perceived facial adiposity and body mass, a meta-analysis was conducted on studies that quantified the relationship between perceived facial adiposity and BMI/percentage body fat. Summary effect size estimates indicate that participants could reliably estimate BMI from facial cues alone (r = 0.71, n = 458).