The study of beauty has many facets with research clearly showing us what biological indicators account for the perception of attractiveness and the subsequent societal implications. But why does beauty matter? Why do our brains infer that attractive people are more valuable social resources than less attractive people [9]? This chapter focuses on why these preferences have come to be so prevalent in modern day society. Conventional thinking asserts that standards of beauty are a gradually learned subjective process that is a product of the media; however, research conducted over the past decades contradicts these widely held beliefs [5]. Theoretical and empirical work has attempted to understand physical attractiveness through evolutionary models of signaling.

The evolutionary view assumes that preferences serve adaptive functions and that the external world provides information to guide biologically and socially functional behaviors [10]. If information was present about a person’s value in our evolutionary past, an advantage would accrue to those who used that information, and those who used signs and signals would be able to leave more genes behind in the following generation [10]. Preferences for certain traits guide individuals to choose mates who will provide the best chance of their own genes surviving [10].

This adaptationist approach identifies adaptations and explicates the selection pressures that formed them in the evolutionary past of an organism [11]. Individuals, viewed as both signalers and perceivers, have traits leading them to respectively display or identify features that are more attractive than others, evolved as a result of having benefits [11]. Evolutionary theorists believe that these traits have been constructed through a process of phenotypic modification by natural selection for gene-propagating effects [11]. From the perceiver’s aspect, physical attributes that individuals are selected to find attractive can be thought of as signs or signals of underlying qualities [11]. In essence, the signalers display signs and the receivers use cognitive and motivational capacities to recognize and act upon those signals [11]. According to this sexual selection and signaling theory, acting upon these signals equate to being attracted to another person. It has been hypothesized that certain salient features have evolved to be attractive because of the benefits, which may be material and/or genetic, that accrue to those who choose mates based upon these criteria [12]. Benefits can be both direct, whereby the perceivers directly gain for themselves and offsprings (e.g., choosing a parasite-free mate who can provide material support), and indirect, whereby the perceivers gain genetic benefits [10].

Theorists have proposed that our shared preferences for attractive facial traits are indicative of genetic fitness and stability and are adaptations to the issues that revolve around mate choice [13]. It is the fundamental assumption of evolutionary-based theories that physical attractiveness is largely a reflection of reliable cues to reproduction, health, and quality. We have evolved to not only pay attention to beautiful people but also seek them out as partners and mates.

Signaling and the potential for exchanges in the mating world is nothing unique to Homo sapiens [14]. Most nonhuman species rely on external traits, such as size, shape, and color of adornments to attract mates [10, 15]. Both avian and mammalian species show preferences for exaggerated male characteristics [15]. Male dung beetles grow large horns, the display of which attracts females and functions to defend tunnels where the females lay their eggs [14, 16]. Presumably, the female dung beetles that appear healthiest attract the males with the largest horns, maximizing the chances of reproductive success [14, 16]. Experimental plastic surgery has shown that increasing the length of a widowbird’s tail by adding feathers produces super-tailed males who enjoy more reproductive opportunities than their average-tailed competitors [17, 18]. Under evolutionary pressures of competition and selection, certain traits may grow to large sizes that need increased amounts of energy to maintain. These signaling traits are sometimes viewed as handicaps (features that impose cost to the individual) and often are more pronounced in male species given that female reproducibility is of a limited resource. A now extinct species, the Irish Elk (Fig. 3.2) had antlers that spanned 12 ft and weighed 80 lbs [16]. On initial inspection, the iridescent blue to green-colored plumage of the large peacock tail appears to have no functional significance other than attractiveness to the opposite sex [9]. It has been thought that these large ornaments and displays have been driven by the struggle to demonstrate valuable heritable characteristics, those that are prized in males by females [16]. In a more obvious way, the cost of developing the ornaments is outweighed by the greater access of females to a prized possession, like a tunnel where females can lay eggs in the example of the dung beetle. In a more subtle way, these obvious handicaps may actually, in fact, demonstrate greater genetic fitness as the ability to overcome the handicap shows that those males must be more viable than others who are not able to essentially “waste” excess viability [11]. It is the “honesty” of advertisement that prevails, because a given increment of display costs the truly fit and healthy relatively less than their less fit sexual competitors [9]. Although not universal, across many species, more ornamented males compared with less ornamented males, have stronger immunity, reduced parasitism, and increased adult survival [19–21]. In addition, feather and skin coloration is known to influence sexual attraction in a variety of animal species, and studies on bird pigmentation have suggested that certain colors may signal immunocompetence and health [15, 22].

It is proposed that perceptions of attractiveness are species-wide, sexually selected adaptations for finding good mates [23, 24]. Features that are considered beautiful and irresistible have evolved in the animal kingdom due to sexual selection, and these preferences provide evidence for claims that human beauty mirrors these tendencies [25]. Just as large antlers, tails, and horns may reflect superior genetic fitness, certain features of humans may also have undergone selection pressures due to particular benefits and be signs of underlying quality. However, in species like humans where there is generally more equivalent expenditure of time and investment for offspring, mutual mate choices have evolved. Human cultures are characterized by mutual mate choice in which both men and women discriminate the desirability of potential mates [11]. Evolutionary psychologists have studied both the animal kingdom and humans and suggest that those human traits that are considered attractive function as markers of biologic condition, health, and reproductive potential.

Current theoretical and empirical findings suggest that mate preferences are based on certain cues that reveal underlying quality [25]. According to the good genes theory, individuals should be attracted to one another in such a way that they are likely to pass on their own genes. The good genes explanation posits that mate preferences favor good-quality individuals due to direct and indirect benefits associated with the selection of healthy partners [26]. Ideally, individuals gain aspects of quality for their offspring by mating with attractive individuals, either by obtaining good genes or obtaining a partner that will be a good parent, or both [15, 27]. Evolutionary biologists account for infant preferences for attractive faces as a tendency to favor anatomical population averages while opposing extremes because those close to the mean are less likely to carry harmful genetic mutations [28]. Aspects of certain physical traits, such as averageness in infant preferences, have been hypothesized to be considered attractive because in effect they are associated with individuals’ health, age, and hormonal status throughout the evolutionary history. For example, in our evolutionary past, individuals may have been selected to choose mates who possessed features of physical appearance associated with pathogen resistance [29]. In support of this, human data from 29 cultures indicate that persons from geographical regions carrying greater prevalence of pathogens value a mate’s physical attractiveness more than those living in areas of little pathogen incidence [29]. The authors argue that physical attractiveness cues may provide more information about the health of a prospective mate when it is more relevant, for example, in areas of higher pathogen prevalence [29]. For example, attractiveness, as assessed by symmetry, was found to be more strongly preferred by the Hadza than those in the UK, suggesting that this trait may be more important in a hunter-gatherer group given that they have much higher mortality rates from birth onward [30]. The cues that have received the most attention include sexually dimorphic characteristics, symmetry, and averageness.

Alternative theories do exist for the evolution of adaptations of attractiveness and attraction. The Fisherian sexual selection view suggests that favorable features do not correlate with fitness except in terms of attractiveness to the opposite sex [9]. Another theory, termed sensory bias, suggests that mate preference arises as an incidental effect of another preference adaptation unrelated to mating that then causes evolution in the opposite sex [9]; see Gangestad et al. for full review [11]. Although the notion that attractive features are cues to “good genes” remains somewhat controversial, most endorse this particular theory.

In most animals and humans, differential parental investment leads to different mating strategies by males and females [23]. Females have greater investment to offspring, whereas males can increase reproductive success by mating with several females; therefore, it would be expected that attractive males have more short-term mating success and attractive females have more long-term mating success than their less attractive peers [23]. This was found to be true with facial attractiveness scores correlating with the number of short-term (but not long-term) sexual partners for males and with the number of long-term (but not short-term) sexual partners for females [23]. Male body attractiveness also correlated with the number of short-term (but not long-term) sexual partners [23].

Overall, and cross-culturally, males and females place differential weight on the value of physical attractiveness, with men typically paying more attention to looks than women [9, 31–33]. In a study of 37 cultures, men valued physical attractiveness and relative youth in potential mates more so than women, whereas women were found to value cues of resource acquisition and financial capacity more so than men [32]. Males are attracted to certain traits that may be indicators of underlying health and fecundity in regards to both reproductive value (measure of future reproductive potential) and current fertility [34]. In regards to attractive traits (e.g., averageness, symmetry, sexual dimorphism), sexually dimorphic characteristics have shown the clearest associations with sexual behaviors [23]. In accordance with this, feminine female faces are consistently found to be more attractive than masculinized female faces. In one study, women with more feminine faces were found to have more long-term sexual partners and also became sexually active earlier than their peers [23]. Recent research has indicated that face and body may make independent contributions to overall attractiveness [34, 35]. Although face ratings consistently are found to be the best predictor for overall ratings, this does suggest that faces and bodies may be signaling different information about potential mates [35]. It has been hypothesized that faces provide more information regarding overall reproductive value, while a woman’s body conveys stronger cues to her current fertility [34]. In support of this and the good genes theory, men prioritized facial cues in long-term mating contexts, but somewhat shifted their priorities to bodily cues for short-term mates [34]. Consistent with prior research, although conditional shifts gave more focus to the body, the face was still a better predictor of overall attractiveness [34, 35].

Although preferences for female femininity have been a consistent feature of attractiveness research, preferences for masculinity in male faces vary across studies. Male face shape may provide information about hormonal status as testosterone is linked to the amount of growth of male secondary sexual characteristics like brow ridge and lower facial structures. It has been proposed that testosterone may be linked to the suppression of the immune system [36, 37], so such features considered to be attractive in males may honestly advertise quality through the ability to overcome the immunocompetence handicap. Only those in superior health condition can bear the cost of high testosterone levels and associated exaggerated secondary sexual characteristics [38]. Females are not only concerned with choosing healthy mates but also concerned with mates who will be able to provide sufficient resources to help progeny survive [12]. Therefore, preferences for certain attractive traits may have evolved because of enhanced reproductive success, either because those having these traits provide better parental care and/or they confer genetic benefits to their offspring with regards to disease resistance [39]. Interestingly and contrary to some predictions, certain groups have found a female preference for feminized male face shapes [40]. These face shapes, however, were also given the positive attributions of cooperativeness, honesty, and good parent [40]. Enhancing masculine facial characteristics increased perceived dominance with associated negative attributions, such as coldness and dishonesty, relevant to relationships and paternal investment [40]. Researchers found a greater female preference for masculinity in men’s faces in Jamaica than in the UK, arguing that male facial attractiveness reflects assessment of paternal qualities as well as genetic quality. Authors argued that increased parasite load and less medical care in Jamaica led to the preference for masculinity of Jamaican women compared to British women, while also arguing that when there is more importance placed on investment, feminine male faces may be preferred [41]. In addition, analyses suggest that the extent to which women rate masculine men to be more attractive (than feminized men) is significantly greater when judging men labeled as faithful than unfaithful (Fig. 3.3) [42].

The benefits from human investment from two parents may have led to these differences and certain changes in preferences. There is evidence that women’s preferences for masculine male face traits change across the menstrual cycle, indicating conditional mating strategies and that women may be more attentive to phenotypic markers of good genes during fertile phases [38]. Female respondents who were in the follicular phase (day 6–14) of the menstrual cycle were significantly more likely to prefer a masculine face than those in other parts of the cycle, providing evidence that women prefer testosterone-related facial characteristics that may indicate immunocompetence when more likely to conceive [38]. Skin coloring is also a sexually dimorphic trait, and females have been found to prefer darker photographs of male faces around ovulation [43]. Clearly a trade-off exists and shifting preferences for male faces may reflect context-specific mate choice strategies for women with a higher preference for masculine facial traits during times of high conception risk when heritable genetic benefits in offspring may be obtainable [38]. Women’s preference for masculinity near ovulation has been supported by four studies in four different countries [38, 44, 45]. Supporting the notion that masculinity in male faces is an important trait relevant to reproductive mating decisions, women’s preferences for masculinity in male faces were found to be highest during the reproductively active age range and lowest around puberty and postmenopause [46]. In addition, studies have shown that women prefer masculinized male faces when judging for short-term relationships than for long-term relationships and also in regards to extra-pair copulations (when women already have a partner), suggesting that these preferences are adaptations that function to obtain superior genetic quality to offspring [19, 45, 47]. These preferences are adaptive as they serve to maximize parental investment and cooperation in long-term relationships (by preferring feminine-faced males) and also maximize heritable benefits of short-term or extra-pair partners (by preferring masculinized male faces) [47]. These strategies likely fall on a continuum, the best choice reflecting a combination of maximizing heritable benefits and also parental investment.

Although complexities clearly exist in preference choice, the fundamental idea of the good genes theory is the prediction that beauty has meaning within interactions because it accurately advertises underlying quality, reproductive abilities, and health, and perceivers have evolved to prefer certain individuals for their healthy status.