symmetry human body biology science

The beauty of symmetry

rats live on no evil star / ta ke ya bu ya ke ta

When I had a routine brain-scan years ago, the doctor exclaimed excitedly: “What a beautiful symmetric brain you have!So I wondered, aren’t all brains supposed to be symmetric?

In fact, are we humans not members of the large group of animals know as ‘Bilateralia’, in which left and right sides of the body should be mirror images? A quick examination of worms, lobsters, spiders, beetles, frogs, and birds shows that basically (with some exceptions like flatfish) this is correct. Looking at ourselves, we notice on each side of our body an arm and a leg (arranged as mirror images) with the same number of fingers and toes. We also notice that our ears and eyes are symmetrically arranged and that only the mouth and some other openings are unpaired, located on the body’s mid-axis.

However, if we look more closely, we realize the symmetry is not perfect (and inside the body much worse still). In most women the left breast is larger than the right and, sadly, more frequently affected by cancer than the other. A study of Greek statues of naked heroes revealed that in most cases the sculptors placed the left testicle lower than the right. And, indeed, the sculptors had observed their male models correctly. (The Greek’s idea of daughters stemming from the left testicle, however, was wrong!). Do these and other, especially facial asymmetries, affect our sense of beauty? Numerous tests support the claim that in humans (and animals) attractiveness depends on symmetry. Apparently human infants and even monkeys display a preference for symmetric patterns, but counter-claims, namely that babies find friendly faces more attractive than symmetric but unfriendly ones, have also been made.

Although many celebrities are prepared to pay beauty surgeons a great deal of money for symmetric facial features, symmetry can be boring (hairdressers are aware of that and the philosopher Immanuel Kant called symmetry ‘sterile’. Well, he lived at a time when artificial beauty marks placed by women into their faces to make them more ‘interesting’, was en vogue). Painters, too, knew that and for centuries have been employing the ‘Golden Cut’ in their works. Moreover, the actor Jean-Paul Belmondo was a hugely popular ‘heartthrob’ of the 1960s despite a greatly asymmetric face, and Miss Paris Hilton and the Japanese dancer Minegishi Minami are beauties with asymmetric faces. The famous actress Marilyn Monroe was also often seen with a beauty spot on her left cheek, seemingly to break perfect symmetry.

Regarding animals, the situation is not one-sided either: True, a stag with asymmetric antlers is not a great sight and a guppy fish in my aquarium with one normal and one abnormally small left pectoral fin, found it hard to be accepted by a female. On the other hand, it’s males with the greatest imbalance of left and right claw sizes that female fiddler crabs find irresistible. But let’s take a look inside the human body: Liver on one side, heart on the other, a spleen off the midline and a gut without any symmetry at all.

And the brain? It may look symmetric, but functionally it ain’t. In right-handed subjects right-side movements, speech, and logic are predominantly located on the left hemisphere; left-sided movements, art appreciation and sensitivity on the right. Even left and right eyes may have different tasks: at least in chickens. Their left eye is used mainly for orientation and their right eye for food identification.

In starlings, research by Hart and co-workers has shown that colour discrimination would be best in the left, and movement perception in the right eye. I’m not a bird, but when I read a palindrome like the one in the title, would it make a difference to my visual system, if I read it from the left or from the right? Perhaps another brain scan can provide the answer. But now I have to buy a pair of shoes and am really glad that my two feet are symmetric and equal in size.

symmetry human body biology science

© Dr V.B. Meyer-Rochow and, 2015.
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