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Human beings have been fascinated by what makes someone attractive for centuries. While some traits are pretty logical and easy to understand – like youthful looking skin, bright eyes and good muscle tone, which all give you a pretty good indication of whether the person is healthy or not – others are harder to pinpoint. It seems we like symmetry, but not too much symmetry, and faces that are closer to the ‘average’ for a population when deciding whether a face is attractive to us.

Interestingly, we start showing these kinds of inbuilt preferences when we ourselves are still babies. In a study by the University of Texas in Austin, infants as young as two months old tended to look longer at pictures of attractive faces as rated by adults. We may never know if this sense is completely innate from birth, or if even children as young as this have been receiving subtle signals and cues from their parents and other adults about beauty. One theory is that symmetry and ‘averageness’ – i.e. how closely a face conforms to the normal and standard features across our species – is simply easier for the brain to process. Quite literally, easy on the eye.

But what exactly makes one face more attractive than another? Understanding the mathematics behind the features we find most attractive is crucial in fields such as plastic surgery, where doctors need to provide expert advice and make sure their patients have realistic expectations of what’s possible.

The golden ratio

Made famous by Leonardo da Vinci’s image of ‘Vitruvian Man’ –although the image doesn’t actually conform perfectly to the mathematics – the golden ratio, golden mean or golden section seems to be important to us aesthetically. From beautiful buildings like the Parthenon to natural objects like spiraling shells and the seeds of sunflowers, we’ve been fascinated by this ratio for centuries. Based on the Fibonacci sequence which starts like this: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55 and so on, the golden ratio is an irrational number like pi, but comes out at around 1.618.

In the human face, it’s been put forward that when the proportions of the length of the nose, and the position of the eyes and the length of the chin correspond to this ratio, we’re more likely to find the owner of that face attractive. Californian plastic surgeon Dr. Stephen Marquardt took this idea even further, putting forward that the ideal human mouth was 1.618 times wider than the nose, and the widest point on the nose should be 1.618 times wider than the narrow tip.

Symmetry

The appeal of symmetry in faces might be a bit easier to understand in evolutionary terms, as unsymmetrical features might well be a sign of an underlying genetic issue or disease. This might be the reason that even animals are attracted to symmetrical faces and features in the mates they choose.

Perfectly symmetrical faces created by facial mapping software, on the other hand, are found to look a little weird and even disconcerting to viewers. Which brings us to another big point…

In the eye of the beholder

While the mathematics behind beauty are certainly interesting, there’s clearly a big subjective element as well. Compare the winners year on year from beauty pageants and magazine top ten’s, and it’s clear that we don’t seem to agree on one set definition of the perfect human face. Even identical twins can have differing ideas of which faces are more beautiful to them. Familiarity also plays a big role, as we’re likely to find someone more attractive the more we’re exposed to their features.

There’s also a lot of research that suggests we’re attracted to partners who remind us of our opposite sex parent – at least the way they looked when we were young. It might make you feel a little squirmy, but there’s a very logical reason for it. When we’re young and vulnerable, the first faces we associate with care and safety are usually our parents, and when it comes time to choose our own mate, we will likely unconsciously gravitate to faces and features that remind us of them.

Where we are in our own lives has a role to play too. Women will frequently rate men with facial scars as more attractive for a short-term relationship than a long term one, for example.

Beauty has and probably always will fascinate us, and for good reason. Attractive people frequently find it easier to get jobs, and are rated as more likely to be intelligent and friendly than their less attractive counterparts. Part of the great thing about being human, of course, is being able to identify our own biases, and hopefully pull ourselves up when we might be judging someone unfairly!