"What is beautiful is good"—but why? A recent article in The Quarterly Review of Biology provides a compelling physiological explanation for the "beauty stereotype": why human beings are wired to favor the beautiful ones.
Studies have shown that humans subconsciously attribute positive social qualities (such as integrity, intelligence, and happiness) to physically attractive individuals. Even across cultures there exists a significant consensus on relative beauty: youthful facial features, including, for women, relatively large eyes, a relatively high craniofacial ratio, and a relatively small jaw. In an article published in the September 2013 issue of The Quarterly Review of Biology, Dr. I. Elia, an independent scholar at Cambridge University, bridges genetics, physical and social anthropology, and psychology to interpret the findings of the "farm fox experiment" in Russia to reveal "a possible and replicable demonstration of the origin of beauty while inadvertently illuminating its ancient philosophical connection to goodness via a plausible neurohormonal pathway."
Silver foxes (Vulpes vulpes) were selectively bred for "friendly" behavior toward humans. Within 20 years, a tame line of communicative, trusting, and playful foxes was achieved. Researchers also noticed that in addition to desirable behavioral traits, the foxes also experienced more rapid development to maturity and displayed more "attractive" and more juvenile physical features, including rounder skulls and flatter faces, with smaller noses and shorter muzzles. That these neotenic changes resulted from genetically controlled alterations in friendly behavior may suggest that to humans, facial beauty signals an individual's relatively greater level of approachability and sociability.
In the experiment, selection for "friendly" appeared to affect genes controlling the hypothalamic-pituitary-adrenal (HPA) axis, which modulates both fear and aggression. Selection to reduce both these states in order to obtain more friendly foxes alters the triad's function, with consequent changes in hormone levels that, due to earlier physical maturation, also affect diverse physical features. Earlier skeletal maturation means that the sutures at the base of the skull fuse sooner, making the skull more domed and giving the higher craniofacial ratio and foreshortened face human beings find endearing.
Natural selective pressure for approachability must have similarly prevailed in the evolution of mammals, because too-aggressive or too-fearful individuals would have interfered with the feeding and survival of offspring. Because young and female mammals are traditionally more involved than males in early feeding, it is not surprising that neotenic faces and behaviors generally appear in young and female mammals—and that this particular emotion-evoking facial structure links to friendly, interactive, calm, trusting, and social behaviors.
Some neotenic changes may underpin the ability to interact, cooperate, and learn in humans and other species. Intuitive or deliberate selection appears to have enhanced the neotenic package, which predisposes to calm, curious, and caring rapport among individuals. Studies have consistently found that relative facial attractiveness in both children and adults (females and males) significantly correlates with social performance and with intelligence measured by IQ. This has set the stage for learning and cooperation within and between several mammalian species, and is likely due to changes in genes controlling the HPA axis, which then produces similar downstream effects in diverse species when rapport behavior is chosen. Although more supporting research is needed, it appears that species as different as bonobos and killer whales may have selected themselves for approachability, with consequent key behavioral and structural traits (including crowded teeth!) that are shared by them, humans, and domesticated animals.
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Elia, I. E. "A Foxy View of Human Beauty: Implications of the Farm Fox Experiment for Understanding the Origins of Structural and Experiential Aspects of Facial Attractiveness." Quarterly Review of Biology Vol. 88, No. 3 (September 2013). www.jstor.org/stable/10.1086/671486