Even across cultures there exists a significant consensus on relative beauty: youthful facial features, large eyes, a relatively high craniofacial ratio, and a small jaw, researchers said.

Dr I Elia, an independent scholar at Cambridge University, conducted the research in which silver foxes (Vulpes vulpes) were selectively bred for "friendly" behaviour towards humans.

Within 20 years, a tame line of communicative, trusting, and playful foxes was achieved.

Researchers also noticed that in addition to desirable behavioural 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 neoteric changes resulted from genetically controlled alterations in friendly behaviour 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 neoteric faces and behaviours generally appear in young and female mammals - and that this particular emotion-evoking facial structure links to friendly, interactive, calm, trusting, and social behaviours.

The study was published in the journal The Quarterly Review of Biology.

(Agencies)

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