Facial appearance affects mate evaluation and selection (Little, 2021; Roth, Samara, & Kret, 2021; Toma & Hancock, 2010). Evolutionary studies investigated morphological characteristics that, across cultures, contribute to physical attractiveness. Based on this, the perceptual evaluation of facial attractiveness is thought to utilize major morphological parameters that are potential indicators of underlying individual quality, namely bilateral symmetry, sexual dimorphism, and averageness (Fink & Penton-Voak, 2002; Grammer et al., 2003; Little, 2021; Rhodes, 2006).

Bodily symmetry is considered a marker of developmental instability in humans (Thornhill & Gangestad, 1994; Van Dongen & Gangestad, 2011) and other species (Møller & Pomiankowski, 1993). However, the effects of sexual selection on symmetry may vary in different species with different ecological niches and mating systems (Kruuk, Slate, Pemberton, & Clutton-Brock, 2003). Despite being a subject of a long and ongoing debate (e.g., Weeden & Sabini, 2005; Grammer, Fink, Møller, & Thornhill, 2003), evidence suggests that facial symmetry increases facial attractiveness. Individuals with more bilaterally symmetrical faces are perceived as healthier and more attractive (e.g., Little, Apicella, & Marlowe, 2007; Perrett et al., 1999; Rhodes et al., 2001; Zaidel, Aarde, & Baig, 2005) and report fewer health problems (Thornhill & Gangestad, 2006).

Sexual dimorphism is another ancient property of metazoans (Kopp, 2012); it appeared no later than gonochorism (Sasson & Ryan, 2017) and is influenced by sexual selection across animal species (Janicke & Fromonteil, 2021). In humans, the femininity of women's faces is considered attractive to men, but preferences for masculinity in men's faces vary across studies (e.g., Stephen, Salter, Tan, Tan, & Stevenson, 2018). Some evidence indicates that sexual dimorphism is related to general health, fecundity, and pathogen resistance (Law Smith et al., 2005; Rhodes, 2006; Rhodes, Chan, Zebrowitz, & Simmons, 2003; Thornhill & Gangestad, 2006), but other studies find no consistent association between sexual dimorphism and health/fecundity (Boothroyd et al., 2017; Boothroyd, Scott, Gray, Coombes, & Pound, 2013; Lidborg, Cross, & Boothroyd, 2022; Rantala et al., 2013; Zaidi et al., 2019).

Averageness (i.e., prototypicality, or its logical opposite, distinctiveness) is another relevant facial feature for attractiveness research. It measures how close an individual's facial proportions are to (or how far they are from) the average proportion in a given population. As soon as recognition of individuality evolved (Leopold & Rhodes, 2010), the degree of distinctiveness would be available for assessment in social and mating contexts. Arguably, it could indicate the level of inbreeding and/or the extent of kin network present in a population. In humans, the positive impact of averageness can be demonstrated by facial morphing, where the more different faces of the same sex contribute to an averaged composite, the more attractive it is considered (Little, 2021; Rhodes, 2006); this effect likely derives at least partly by correcting individual imperfections, up to roughly 30 faces (Langlois & Roggman, 1990). Averageness is rapidly processed by the brain (Trujillo, Jankowitsch, & Langlois, 2014) and could also tap into a preference for familiarity (Bohrn, Altmann, Lubrich, Menninghaus, & Jacobs, 2013). Moreover, facial averageness is cross-culturally preferred—not only across various European populations but also in the Hadza of Northern Tanzania (Apicella, Little, & Marlowe, 2007)—which suggests universality.

Previous studies have analyzed effects of these facial components independently (for a review see, Rhodes, 2006; Little, 2021). However, everyday facial judgments likely consider them all simultaneously. Grammer et al. (2001) showed that attractiveness assessment integrates facial and bodily traits in a “fast and frugal” way according to a heuristic that has been described as “avoid the worst” – meaning that unattractive features are used for attractiveness decisions rather than highly attractive features. Hence, in order to increase ecological validity, different basic parameters of the face – such as skin texture and color, facial shape, eye and hair color, facial symmetry, and degree of sex-typicality – should be simultaneously investigated in the same study (Apicella et al., 2007; Little et al., 2007). Very few studies have proceeded with this extension of scope to examine relative contributions to facial attractiveness of certain features over others. For instance, Mogilski and Welling (2017) found that individuals prioritize cues to sexual dimorphism over symmetry and healthy coloration, particularly for male faces. In contrast, facial symmetry and healthy coloration were more important in preferences for female faces. Foo, Simmons, & Rhodes, 2017 evidenced the importance of sexual dimorphism, averageness, and symmetry in perception of attractiveness but reported only a weak association between health and facial cues to attractiveness. Jones and Jaeger (2019) found that averageness has a larger effect than symmetry when using manipulations or naturalistic paradigms, but when using machine learning algorithms attractiveness is predicted by shape averageness, dimorphism, and skin texture, but not shape symmetry.

Not so many studies have addressed preferences beyond a single or limited number of North American or Western European populations. Jones and Hill (1993) demonstrated in five populations that age-related traits and averageness (in both sexes) and neotenous and feminine features (in females) influence facial attractiveness. Using European faces, Kočnar, Saribay, and Kleisner (2019) found that sex-typical and average facial traits were positively associated with attractiveness by raters across 10 cultures, while fluctuating asymmetry had no effect. The evidence based on Namibian and Cameroonian faces showed a similar pattern of null preference for fluctuating asymmetry and moderate preference for facial averageness (Kleisner et al., 2017). Using samples from five distant populations, Fiala et al. (2021) examined possible moderating effects of averageness, age, body mass, and facial width on human attractiveness. While women's perceived femininity was positively related to perceived attractiveness, shape sexual dimorphism and averageness were not associated with either perceived facial sexual dimorphism or attractiveness (Fiala et al., 2021). While certain studies evidenced the universality of attractiveness perception (Coetzee, Greeff, Stephen, & Perrett, 2014; Cunningham, Roberts, Barbee, & Druen, 1995; Fink & Neave, 2005; Jones, 1995; Langlois et al., 2000; Rhodes et al., 2001), others acknowledged local variation influenced by sociocultural factors (Jackson, 1992; Kara & Özgür, 2023; Little, Jones, Debruine, & Caldwell, 2011; Voegeli et al., 2021)

We extend these approaches here, but our study is unique for three main reasons. First, many previous studies of the preferences of facial symmetry and typicality used facial stimuli from one or a small number of mostly WEIRD (i.e., Western, Educated, Industrialized, Rich, and Democratic) populations (Apicella & Barrett, 2016; Henrich, Heine, & Norenzayan, 2010). Second, very few of these studies compared large numbers of standardized natural facial portraits from various populations worldwide (e.g., Kleisner et al., 2021; Voegeli et al., 2021). Third, we investigated facial perception based on non-manipulated faces collected from members of the same local population. This is a critical point because the perception of faces in a specific population is neither evolutionarily nor socially independent from the variation of facial morphologies present in that population. Using local and non-manipulated faces, therefore, represents the most ecologically valid setting, sensitive to both morphological and perceptual components of facial variation. Thus, in summary, we aimed to investigate in both sexes the relative importance of facial distinctiveness, sex typicality, and symmetry in terms of their effects on human facial mate preferences from populations across the world.