One of my daughters is left-handed. This may not sound particularly unusual, but actually there are many more male left-handers than female. And nobody seems to know why there is this disparity. I guess this is the root of my fascination with the topic of handedness: it seems to pop up everywhere. Often it cannot be explained. And its effects can be more far reaching than might otherwise be expected.
Today I am going to confine my discussion to human handedness. Maybe I will look at other aspects of asymmetry another day. I like to think in terms of symmetry, or lack thereof, as handedness is just the obvious manifestation that …
Handedness is thought of as being a preference for using one hand over the other, where strength or precision is required. It goes beyond hands. I, for example, am right handed, right footed and left eyed. Testing which eye is dominant is interesting. Here is how to do it: With both eyes open, point with an index finger up to a corner of the room at ceiling level. Then, while keeping your hand still, close each eye in turn. With one eye, the finger will not appear to point to the right place. With the other, your dominant eye, it is still lined up.
I am not sure what use this information can be put to. I have noticed that, if I am working from a paper document at my computer, I prefer it to be on my left, which is handy as, obviously, my mouse is on the right.
Handedness seems to be related to the “wiring” in the brain, as there is no discernible difference between right and left arms that cannot be accounted for by the preferential use of one of them. The human body is an odd mix of symmetry and asymmetry. On the inside, some organs come in symmetric, mirror image pairs [e.g. kidneys, lungs]; others are on just one side [e.g. liver, appendix]; and others are central, but are structurally asymmetrical [e.g. heart, stomach]. The brain looks symmetrical, but each lobe performs different functions.
I used to wonder whether left handed people’s brains were programmed the other way around, but this is obviously not the case – otherwise I would be right eyed, for example. There is a very rare condition where an individual is completely “back to front” – their entire body is a mirror image of the “normal” arrangement. Sadly, they tend to be prone to a number of health issues and have low life expectancy.
So much for the inside of the human body – what about the outside? Here symmetry is the order of the day. We are almost exactly mirrored from left to right, with only very minor universal exceptions [I can only think of one and that only occurs in males]. Research has shown that we tend to find such symmetry attractive. Subjects have been asked to rank pictures of faces in order of attractiveness and they consistently put the most symmetric at the top. The theory is that the symmetry is a sign of “healthy” genes and, hence, this is a tool we use to select a genetically attractive mate.
There is a saying: “Beauty is in the eye of the beholder.” It seems like it is actually in the brain and could even be quantified and measured, which I, for one, find rather disconcerting. But it does lead to the geek’s perfect chat up line: “Darling, you are so symmetrical.”