OFF-TOPIC: Musing on handedness

I have always be fascinated by the concept of being right- or left-handed. Almost all of us have this asymmetry between the strength and precision of movement that our hands deliver. Very few people are ambidextrous – i.e. exhibit no handedness at all. Although most people are right-handed, male left-handers are not too uncommon. Female lefties are rarer and nobody seems to have a clear explanation for this disparity.

As nowadays, in western cultures anyway, young children are encouraged to find their own “best hand”, it is fairly safe to say that handedness is inane, not learned. What is the evolutionary benefit of handedness? There are various theories, but nothing definitive. I am aware that being left-handed can be a challenge [I am right-handed, but have a daughter and various friends who are left-handed]; so many everyday things are very oriented to right-handed operation.

It is curious to me that writing has a handedness. In European languages, and many others, text is written left to right. This strongly favors right-handedness. Left-handers always have to take care to avoid smudging and often end up holding their pen in quite an awkward way. Some left-handed children start out doing mirror writing [unsurprisingly, IMHO]. Some other languages – notably Arabic and Hebrew – are written right to left, but I do not believe there is any greater concentration of left-handers in the countries that use those languages.

Historically, there have always been bad feelings towards left-handedness [for no logical reason]. For example, the Latin word for “left” is “sinistram” which is where the English word “sinister” is derived from. Another example is, if someone is seen to be clumsy, accident-prone or just awkward, they might be called “cack-handed”. This term means left-handed. It refers to the reason why, in some cultures, they never eat with their left hand, as it might be unhygienic. I will leave that there …

It is not just hands that are asymmetric; feet are too. You can test someone’s “footedness” by having them run towards a ball and kick it. Everyone has a foot they prefer and will almost always use it under these circumstances. I am right-footed [as well as right-handed].

Eyes also have an asymmetry, though, in this case, it makes some more sense. We have two eyes to give us stereoscopic vision so that we can judge distance well. Carnivores tend to have this kind of vision; herbivores [their prey] have something more like all-round vision. Our brain calculates how far away something is using trigonometry. We point our eyes towards something and all that is needed to calculate the distance is the angle that there eyes are turned in [and the distance between our eyes]. Except that they do not work like that. One eye [the dominant one] always looks straight forward when looking into the distance and the other eye does the turning. Same kind of calculation – just different mechanism. You can find out which eye is dominant in yourself quite easily. Look with both eyes at an object some distance away; look up to the corner of the ceiling for example. Now point with one finger at the object and close each eye in turn. With one eye, the finger is still pointing at the object; that is the dominant eye.

I discovered that I am “left-eyed” [despite my right-bias of hands and feet], which I thought was surprising, as I would expect them all to be linked. This was verified when I decided to try archery. The first thing the instructor did was to check everyone’s dominant eye. He stood in front of us and could check the alignment. He confirmed that I was left-eyed. The result was that I needed to use a bow left-handed, otherwise I would be unable to aim. The good news is that, although I am right-handed, I am not strongly so and I could cope quite well.

It is well known that the human brain has two hemispheres; the left one controls the right side of the body and vice versa. The right brain is where “artistic” stuff happens. It is, hence, commonly suggested that left-handers are more likely to be artistic. This sounds logical and may be true, but I am unsure what this says about people, like me, with “mixed handedness”.

As I understand it, handedness is not generally observed in other species, though I am curious about how that might have been determined. Also, the way our eyes work is more efficient that having the two eyes move to the center, so it is quite likely that carnivores do have a dominant eye. Again, I am unsure that I can figure out how to test that hypothesis.

What is interesting is that handedness, as a concept, occurs in many contexts; the Universe seems to favor this asymmetry. A good example is organic molecules. Organic chemistry is the study of carbon compounds. A carbon atom commonly connects to four other atoms. The result of this is that such a molecule could form in two ways, which are mirror images of each other; commonly termed the left- and right-handed forms. If you make such an organic compound in a lab, as you might expect, there is a 50:50 mix of the two forms. However, these type of molecules made by living systems are always one or the other and I have never seen a clear explanation of why this might be the case. This leads to some interesting effects. For example, normal sugar is “right-handed”. If you synthesize left-handed sugar. It looks the same and reacts chemically in the same way as right-handed. It tastes sweet in the same way [which is surprising, as I would have thought that the taste receptors would expect right-handed molecules]. It is not digested, so it appears to have no dietary calories, which is what I would anticipate.

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