Stayin’ alive

What disco tells us about our evolutionary past.

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Francis Galton was clearly headed for the academic high country. Born in 1822, he could read by age two, had learned some Greek and Latin by five, and was delighting his illustrious family (both sides of which boasted Royal Society fellows) with recitals of Shakespeare and Keats by his sixth year. A cousin of Charles Darwin, he went on to dabble in linguistics, psychology, anthropology, eugenics (in fact, he invented the term), tropical exploration, geography, meteorology and statistics.

The psychometric test you suffered in your last job interview was based on the discipline he pioneered, and every time you utter the phrase ‘nature versus nurture’, you’re quoting him. Galton was the first to wield statistical methodology in his research of human differences, and the inheritance of intelligence. He also used groundbreaking questionnaires and surveys to collect his data.

Such was the man’s cerebral industry that even when he got things wrong, he often blessed some other discipline with his insights. For example, he was convinced he could revolutionise law enforcement by characterising the typical criminal face—a sort of universal identikit police might use to spot villains before they had even offended. By superimposing photographic portraits from a rogues gallery, he set out to create a composite of the average felon’s visage. In the end, it did nothing to stamp out crime, but an unexpected and mysterious result would spawn a new branch of evolutionary psychology more than a century later. The more portraits Galton added to his composite, the more ‘attractive’ the general­ised face seemed to become. When he tested his inkling among colleagues, they came to the same conclusion. He published a paper in 1878, contesting that if you add enough average features, they eventually meld into good looks.

Galton had stumbled upon a phenomenon we now call averageness. If you’re seeking a distinguished mate, stop now, and embrace mediocrity instead. It seems we have some innate sense of the unexceptional, which we interpret as an ideal average of all human genetic traits.

In 1990, psychologists Judith Langlois and Lori Roggman at the University of Texas at Austin put Galton’s theory to the test. They scanned 192 faces of Caucasian men and women, then created 2-, 4-, 8-, 16- and 32-face composites in a computer. They showed those compound portraits—and the originals—to 300 judges, who ranked them on a five-point scale of attractiveness. The 32-composite face was their clear favorite. And it’s not just a Western thing: similar studies on other ethnicities have returned the same results, whether they were shown faces of their own people or Caucasians. The proof of the pudding lies in the fact that researchers can make individual faces more or less attractive to test subjects just by moving their configurations closer to or further from the average. Humans universally zero in on the norm, not the novel, a tendency recently dubbed koinophilia (from the Greek, koinos, meaning ‘the usual’ or ‘common’).

These and other studies challenge the convention that beauty is a cultural artefact. Instead, our preferences may be shaped by biological cues writ by evolution. If your aesthetic preferences simply feel like instinct, you’re probably right on the money. Our perception of human beauty may in fact be a reflex mathematical calculation, an acute sensitivity to facial properties and proportions. And we’re not so much scanning for perfection as staying on the alert for flaws. An unremarkable face or body sends us a signal that this individual has completed a normal, healthy development, and that’s all we need. Striking features could in fact be interpreted as aberrations—clues to genetic mutation or exposure to environmental stress that our own genes warn us against. This is more than some subconscious hunch: studies across species have shown such departures from the mean have consequences such as poor health, lower survival and fewer offspring.

So just what is ‘normal’ to our primal eye? To get to the bottom of that, we need to delve deep into our evolutionary past, back to the Cambrian, when animal body plans were only just taking their contemporary form. We, along with 99 per cent of other creatures, evolved a shape that is bilaterally symmet­rical: if you stood above an animal’s back and drew a line from its head to its toe, you would see that both halves are externally identical.

Beauty, it seems, is not just a matter of personal taste but rather a matter of measurements, geometry and calculations. Kendra Schmid, assistant professor of biostatistics at the University of Nebraska Medical Center, uses a formula based on 29 different points on the face. The score starts high and works its way down. Though all 29 points are taken into consideration when scoring a person’s attractiveness, some measurements carry more weight than others—symmetry, proportion, and the “Golden Ratio” are key.

Symmetry, for the purposes of mate selection at least, remains our best indicator of evolutionary fitness. If someone’s body and features appear balanced, we assume their genes are good. There’s plenty of data to back this up: the ancient Greeks had no recourse to 3D scanners, but even they suspected that physical equilibrium is a vital criterion in the assessment of beauty.

In 2008, researchers at Brunel University in London created 3D digital replicas of the bodies of 77 adults, then measured them for symmetry. To rule out any bias around facial features, the team removed the models’ heads and applied the same neutral ‘skin’ colour to all. Then they got 87 volunteers to rate the attractiveness of the rendered bodies, guided solely by visual appeal. Both men and women zeroed in on the most symmetrical bodies, declaring them most attractive—an emphatic result, but still more fascinating for the fact that many discrepan­cies in the models’ symmetry were tiny. As indeed they are in real life; discrepancies between the left and right sides of a human body typically range between one and three per cent, yet we have some preternatural ability to spot and estimate them.

Or do we? Some researchers think we run a system of proxy indicators instead. The Brunel team also found that the most symmetrical of their models came from men with pronounced masculine traits—they were tall, with broad shoulders and smaller hip-to­waist ratios. Likewise, the women with larger hips, longer and more slender legs and larger breasts also scanned the most symmetrically. (Intriguingly, an earlier Brunel study concluded that more-symmetrical people tend to be better dancers.

In other words, an impressive display of disco moves is one way a male can advertise his physical fitness, and offers females the visual cues they need to make an informed choice.)

This is easier to accept. After all, you have to presume that assessment of subtle physical minutiae would be hampered by that exclusively human trait, clothing (one reason faces are so critical to our evaluations). Easier to read a set of unambiguous proxy indicators instead. ‘Wait a minute,’ you’re thinking by now, ‘haven’t these studies simply confused correlation for causation?’ Which came first? Broad shoulders and large breasts, or symmetrical bodies? If someone has all the desirable reproductive traits already, isn’t symmetry just a coincidental nice-to-have?

The popular website Hot or Not invites users to rate the physical appearance of other users. Image researcher Pierre Tourigny sorted the results by rank and created digital composites to compare facial features. The composite that was the average of all users was most similar to the individuals that scored above 8.0—indicating that humans favour partners with an ‘average’ gene set.

To answer that, we need to look beyond the messy human condition, complicated as it is by modern phenomena such as gold-digging and silicone implants. We need to look at our wild, unclothed relatives and the role of symmetry in their mate selection. Every subsequent study points to the fact that it is, while not the sole determinant in mate choice in the wild, a very important one. When scientists at the University of Bristol in England fitted different colored bands to the legs of male zebra finches, females overwhelmingly chose males with the same colour and number of bands on each leg.

Female scorpion flies in a University of New Mexico experiment showed they could assess the sameness of a male’s wings to an exacting degree, possibly aided by his pheromones, which inexplicably vary with his symmetry.

Harems of North American elk are overwhelmingly monopolized by those bulls that not only have the biggest rack of antlers, but are also the most symmetrical. After all, a female will reason that if a bull’s rack is intact, he must have won all his fights. A vanquished bull with a broken antler will lose his harem and have trouble attracting another.

Male guppies confident of their symmetry have been observed to display both their sides equally to prospective females, while lopsided ones tended to accentuate the positive, putting only their best side forward.

In humans, symmetry may have been transcended by more convenient, more legible cues, but it remains a critical tick box on the checklist of sexual selection.

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