Science Questions

Why do we have "handedness"?

Tue, 4th Feb 2014

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Kenneth Silva asked:

Why are people either right-handed or left-handed? What possible benefit does that have over being ambidextrous? I find I am right-handed, right-footed, and even right-eyed! When I wore single-muff headsets on my job, though, I preferred them on my left ear and not my right, so that's a bit of a question.


And, do animals also display handedness?


Thank you.

Ken Silva

Laveen, AZ





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I believe it could be possible due to the genes in one's body where one is more dominant than the other. In humans probably the right one is more dominant than the left one which leads to most people being right handed.

Another reason could be that because most people have the general perception that everyone writes with right hand therefore when they teach their kids to write they make sure that the kids hold the pencils/pens in their right hands. If the kid switches over to the left hand most parents will observe for a short time and then after watching that there is no improvement will encourage the kid to switch back to the right hand. Also most day to day activities demand the kid to use it's right hand like using a mouse etc. Eventually over time the kid has more practice of using his right hand that he probably becomes right handed. athemyahba, Sat, 8th Feb 2014

the left side of the brain is known to control the right side of the body, but it's also known as the side to control logic and "smartness", while the right side is known to be "artistic". Because of this more right handed people are known to be smarter because when they use that hand (or side of body) they activate the movement functions in the left side of your brain. Focused_science, Tue, 11th Feb 2014

IIRC the number of lefties in the UK has been increasing since the 1950s, when primary schools stopped insisting on rigththanded writing, sinistral tools (particularly scissors) became more generally available, and the Royal and Ancient allowed golfers to use lefthanded clubs.

We now know that sinistral CEOs and the like earn significantly more than their dextral counterparts in practically every industry, and indeed the frequency of lefthandedness among  CEOs is much higher than among the genral population.

AFAIK genetics doesn't usually work at the "5 - 10% level".  Significant genetic effects in most mammals are either 50-50 (male/female ratio)  or "very rare". So my hypothesis  is that 50% of the human race cannot be lefthanded, due to a minor genetic defect associated with the exceptional demands placed on the human brain and nervous system by walking upright and having an enormous and very subtle vocabulary. This is supported by the fact that apes and to some extent dogs (a species that responds to subtle human expressions) and some birds (which have remarkably wide vocabularies) appear to be handed.

Society copes with the inherent disability of dextrals by decreeing that life will in general be dextral and the other 50%, mostly born ambidextrous, have a choice. This then only disadvantages the very few who are genetically predisposed to lefthandedness. Of the 50% ambis, it is reasonable to assume that half will "go with the flow" leaving about 25% who choose to be different, and the trend seems to be towards this number when social restrictions are abandoned.

The observed high incidence of lefthandedness among scientists, mathematicians, artists and composers (but not musicians - lefthanded saxophones are rare, and a leftie violinist is a health and safety hazard in an orchestra) seems to correlate with notions of originality and abstract thought. 

The universal availability of toilet paper also has a lot to do with it. alancalverd, Wed, 12th Feb 2014

One theory is that the degree of left or right domination in  a species has to do with the whether a species is more cooperative or competitive, or has a kind of mixed strategy. Essentially, there is often an advantage to being different handed than your enemy, but same handed as your friend, and the researchers use professional sports like baseball as an example of this. cheryl j, Thu, 13th Feb 2014

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