The Pleasure Instinct: Why We Crave Adventure, Chocolate, Pheromones, and Music (22 page)

Needless to say, this finding was not consistent with the prevailing theories of child development at the time. Before Langlois began her research, many researchers assumed that preferences for attractiveness were based on the gradual learning of standards within a culture through a variety of sources (for example, media and social experiences) and that these emerged much later during development. Her data are at odds with this view, since these infant subjects have presumably had very limited exposure to such forces, in that they are preverbal and only two months old. Rather, these findings suggest that preferences for attractiveness are either in place at birth or shortly thereafter.

At present, many studies have shown remarkable agreement across raters from different age, gender, and cultural groups in terms of facial attractiveness rankings. Cross-cultural studies have been done with people in the United States, throughout Europe, China, Korea, South America, and Asia using multicultural faces, with fairly consistent agreement on which faces are the most attractive. A major question that is the focus of much investigation is what features humans use to make determinations about attractiveness and why,

Studies by evolutionary biologists and psychologists have found that people sometimes find the average attractive. Take a thousand faces, average their spatial characteristics, and you get a new face representing the group norm, which is generally rated to be slightly above average in attractiveness. In his classic text on the evolution of human sexuality, anthropologist Donald Symons hypothesized that natural selection drives adaptations, where at the population level, the optimum value of some trait is likely to be the mean. In this respect, a preference for the average value of a trait such as facial characteristics would be wise, since it would push the chooser toward mates with optimally adapted facial traits for things such as breathing, chewing, and any other functions linked genetically to the development of facial features. Randy Thornhill and psychologist Steve Gangestad theorized that a preference for averageness occurs because for some heritable traits, the mean value represents maximal genetic heterozygosity (allelic diversity).

Other studies have found that people tend to focus on secondary sex characteristics when making judgments of attractiveness. In humans and many other species, hormonal changes occurring at puberty can actually handicap an individual. For instance, increased testosterone production in adolescent males leads to increased musculature and energy expenditure. These changes, in turn, raise the metabolic demands of the body and draw resources away from other systems, including immune functioning. Since testosterone production creates a draw on immune function, it may be less costly for genetically fit males to have high levels of testosterone than for those more susceptible to environmental and/or genetic perturbations (for example, pathogens, maladaptive environmental conditions, genetic mutations). Likewise, increased estrogen production in pubertal girls indicates reproductive potential and fertility. Reproductive effort places increased metabolic demands on a woman’s body and draws resources away from other important biological processes, including immune function. Hence, secondary sexual characteristics of the face that become exaggerated at puberty (such as an extension of the lower jaw and broadening of the brow ridge in males) may be honest signals of phenotypic and genotypic condition.

In addition to averageness and attention to secondary sexual characteristics, many studies have found a strong relationship (perhaps not surprisingly) between ratings of facial attractiveness and fluctuating asymmetry of the face. Indeed, as mentioned earlier, in their extensive review, Anders Moller and Randy Thornhill found that in most species, the correlation between fluctuating asymmetry and mating success was strongest for body parts that are secondary sexual characteristics. The face is one such body part, since, as we have seen, it is replete with secondary sexual characteristics that become differentiated at puberty.

Numerous studies have demonstrated that both facial and body symmetry involving secondary sexual characteristics are related to reproductive success and health in general. In a diverse range of species tested, increased fluctuating asymmetry has been shown to be related to decreased fecundity, growth rate, survival, and metabolic efficiency. For instance, increased fluctuating asymmetry in men has been shown to be related to a number of fertility measures. Population biologist John Manning and his colleagues from the University of Liverpool studied males referred to a reproductive medicine clinic at a local hospital for routine semen analysis.They found that men with greater body asymmetry had fewer numbers of sperm per ejaculate, lower sperm speed, and reduced sperm migration relative to their more symmetric counterparts. In women, breast asymmetry has been found to correlate negatively with fecundity and to the probability of marriage.

Other studies have shown that body symmetry is related to how efficiently our bodies use energy. If one has a normally low metabolic cost associated with the maintenance of body processes, this should theoretically free energy for use in other ways, such as maximizing developmental homeostasis. Consistent with this ideal, Manning’s group has also found that people with greater body symmetry exhibit a lower resting metabolic rate, measured as oxygen consumption at rest.

The relationship between overall physiological health and body symmetry has also been examined by several investigators. Gangestad and Thornhill gave a series of health questionnaires to 203 romantically involved couples where both the man and the woman rated self and partner. The questions asked about the individual’s current condition in eight specific physical health domains, including muscularity, energy, stamina, vigorousness, robustness, lethargy, physical tightness, and cardiovascular fitness. The researchers found a significant negative correlation between a composite physicality score (summed from the individual domain scores) and body asymmetry. As asymmetry increased, perceived general physical health decreased.

Other investigators have found similar results when focusing just on facial asymmetry. In a study of 101 college students, evolutionary psychologists Todd Shackleford and Randy Larsen examined the relationship between facial asymmetry and a broad of range of physical, emotional, and psychological health indicators. Head shots of students were taken and used to extract estimates of facial asymmetry using bilateral measurements at the outer eye, inner eye, nostril width, cheekbone width, and jaw width. Each subject was also given an extensive battery of health questionnaires concerning mood and emotional state, personality, life orientation, sociability, impulsivity, and general symptomatology. Additionally, subjects were requested to complete reports on their daily activities, moods, and physical symptoms twice each day. These included standard physical symptoms such as headaches, trouble concentrating, runny nose, sore throats and coughs, gastrointestinal problems, and so forth. Finally, each participant had his or her overall aerobic fitness assessed by measuring cardiac recovery time following a standard exercise protocol to raise their heart rates to at least thirty beats per minute beyond resting state.

A separate set of college-age observers were asked to rate each photograph of the subjects along a number of dimensions including attractiveness, happiness, reliability, agreeableness, intelligence, emotional stability, activeness, and others. The overall results of the study painted a complex picture revealing how variation in facial asymmetry impacts several key aspects of daily life in the bearer and how others view them.

In terms of physical health, subjects with greater facial asymmetry were more likely than their symmetric counterparts to report negative physical symptoms, such as backache, muscle soreness, reduced vigor, and trouble concentrating. They were also more likely to complain of depression, perform more impulsive acts, and view their lives as being outside of their personal control. Men with greater facial asymmetry, in particular, tended to score higher on measures of mania and schizophrenia components of the Minnesota Multiphasic Personality Inventory (MMPI), a classic clinical assessment, than those who were more symmetric. Consistent with this observation, several studies have now shown that schizophrenia in adults and hyperactivity disorder in boys are both associated with increased body and facial fluctuating asymmetry.

On the flip side, individuals with relatively more facial symmetry when compared to their counterparts were more likely to be optimistic, view themselves as superior, and score higher on measures of narcissism. Interestingly, extroversion seems to correlate positively with the degree of facial asymmetry in women and negatively in men. Women with more facial asymmetry tend to be more extroverted, while men tend to be more introverted.

Independent judgments by external observers were also systematically related to the degree of facial asymmetry in the subjects. Individuals with greater facial symmetry were viewed by others as being more conscientious, intelligent, active, agreeable, and genuine than those with less symmetry.This study confirms other reports that facial asymmetry correlates with a number of important markers of physiological, emotional, and psychological health.

Thus far we have found that increased body and facial asymmetry are associated with decreases in certain indicators of fertility, as well as self-reported physical, emotional, and psychological well-being. But does greater facial symmetry translate into improved mating success? In other words, do people actually have a preference for symmetric mates?

Symmetry is a basic property that is preferred and sought after by newborns and toddlers alike. They recognize more quickly and exhibit greater pleasure in viewing symmetric objects than those that are asymmetric. I have shown in earlier chapters that an anatomical and developmental imperative exists for symmetry-seeking almost immediately after birth, since it represents an optimal form of stimulation for experience-expectant maturation of the primary visual cortex and additional downstream visual areas (for example, V2, V3, and inferotemporal cortex).

The preference for symmetry right after birth would be expected to continue through childhood, since synaptic pruning of these visual cortical areas continues for decades.This early preference thus forms the basis for a fondness of symmetry in adults. Moreover, since body and facial symmetry are related to general health (and are, hence, potential fitness indicators), an inborn preference for symmetry that mediates normal brain growth and development would be a perfect trait to be co-opted through sexual selection mechanisms. If this scenario is true, one would predict all six of the following conditions to be true as well.