It’s everywhere in our culture, even in our language. Right is right, and left is what’s left. The term dextrous literally means right-handed, and sinister, of course, means on the left. But there doesn’t seem to be any intrinsic reason why human evolution has favoured right-handedness over left-handedness. It’s true that the hemispheres of the brain have their own specialities, but this, I think, only takes the question back a step.
Apes, apparently, don’t have a preponderance of right-handedness over left-handedness. Cats are interesting, though. in that female cats are more likely to favour their right paw, and male ones their left. But the absolute dominance of right-handedness is very much a human trait.
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A right-handed default may be the causal-effect of anatomy bias, in the body favouring the path of least resistance/exertion optimal-energy wise, corresponding with organ-placement and the natural flow of energy.
According to The Naked Ape by Desmond Morris, right-handedness evolved because of how women care for infants: it is better to hold the infant against their left breast because that is closer to the heart, so the infant can feel and hear the mother’s heart beating. This helps the infant calm down and sleep. So the mother would use her left arm to hold the baby, thus leaving her right arm free to do things. Hence over time the right arm became dominant in terms of environmental manipulations. And by virtue of some biological principle the name of which I forget, mutations affecting one sex will tend to pass onto the other sex over time. Hence why men have nipples, I suppose.
So most people are right handed. This also explains why left handedness is associated with genetic instability i.e. high mutational load, including autism and advanced paternal age. Also with being left wing, as funny as that is. And true.
I suppose which begs the question, why is the heart on the left?
Traditionally, the heart is the seat of the emotions. We know, or at least we think we know, that this isn’t true, but it’s an obvious thing to think, since the heart can very quickly respond to all sorts of emotional states, especially those involving, for want of a better term, matters of the heart.
“The narrow-beam, precisely focussed, piecemeal attention of the left hemisphere, aimed at a particular object of interest, is, as we have seen, the kind paid by an animal locking onto its prey. In humans the left hemisphere is designed for grasping, controls the right hand with which we grasp (as well as those aspects of language which enable us to say we have ‘grasped’ something – pinned it down) and helps us manipulate, rather than understand, the world. It sees little, but what it does see seems clear. It is confident, tends to be black and white in its judgments, and jumps to conclusions. Since it is serving the predator in us, it has to if it is to succeed. It sees a linear relationship between the doer and the ‘done to’, between arrow and target.”
McGilchrist, Iain. The Matter With Things: Our Brains, Our Delusions and the Unmaking of the World (p. 43). Perspectiva Press. Kindle Edition.
I looked it up, apparently it is called cardiac looping where the heart inside the developing embryo moves from the center slightly to the left in order to allow for the development of blood vessels and other heart-related structures. So it has some biological-structural reason to be slightly off-center in the body. Either that or it’s just a fluke of evolution.
Right-handedness (the preference for using the right hand for tasks) is another aspect of left-right asymmetry in humans, and is largely neurological, such as Iain McGilchrist describes in the quote above, rather than anatomical like the heart’s positioning.
The brain is also asymmetrical. “Asymmetries in the human foetal brain are visible to the naked eye as early as the 11th week of gestation.”
McGilchrist, Iain. The Matter With Things: Our Brains, Our Delusions and the Unmaking of the World (p. 44). Perspectiva Press. Kindle Edition.
“Contralateral control of the body by the brain is a result of the crossing of nerve fibers during early development, primarily at the pyramidal decussation in the brainstem. While the precise reasons for this cross-wiring are not completely understood, several theories suggest it may be related to evolutionary adaptations that optimize sensory processing, motor coordination, and spatial awareness.”
(My translation from the German. Source: Professor Erich Grond, my teacher in Nursing school.)
That’s a good point, and it could also just as easily fit with my explanation. Because holding infants to the left side was evolutionarily selected for, right-handedness became dominant; as right-handedness became dominant this caused the relevant areas of the left brain hemisphere to specialize more in terms of motor control and spatial awareness as compared to those same areas in the right hemisphere. It could also be the opposite, as you say, but then the whole heart thing would seem an unrelated coincidence.
I’m trying to figure out why the hemispheres of the brain control opposite sides of the body. Looks like there are different theories but none of them really make a whole lot of sense, at least to me.
I’m sure right handedness is indeed related to other important organs and brain functions being on the left, but this just begs the question, why are they on the left? Is there any advantage to this?
Why not the left? The brains of mammals are very similarly split into two halves, and are asymmetrical. Of course, those running around on all fours have different needs, but I think that it could have been the other way around - but it just isn’t.
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