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Why are there less left handers than right handers

Why are there more right-handed people than left-handed?

  • And so being left-handed can have knock-on effects on the way the brain is arranged;
  • Why could this be?
  • But why are there more left-handed men than there are left-handed women?
  • Pelham Barton, Birmingham, UK I dont know how much truth there is in this but I was told that it was down to brain development in the womb;
  • As in a market economy, having a near monopoly of something that is in short supply will be a successful strategy;
  • Quentin Langley, Woking The claim that left-handedness is a recessive trait will not quite do.

David Colville, Glasgow Conventional wisdom is that handedness is controlled by a single gene and that left handedness is a recessive trait. Thus, in an average group of four people, one will be left handed, two will carry the trait, and the fourth will be a pure-blooded right-hander.

However, left-handed people are routinely trained into right handedness by well-meaning parents and teachers, so the population of left handers is underrepresented. I have heard that about one in six is left handed. Genes spread according to whether or not they confer any evolutionary advantage - ie enable you to have more descendants. My understanding is that left-handedness is associated with right brain thinking which is more creative but less logical.

Should this confer evolutionary advantage?

The mystery of why left-handers are so much rarer

If you are the only creative person around you will clean up by monopolising the advantages that creativity can bring you. In a population that is dominated by creative thinkers a minority of logicians will be successful. As in a market economy, having a near monopoly of something that is in short supply will be a successful strategy.

But your monopoly will not hold. If your strategy is genuinely successful you will be better able to bring up a large number of children: In his book "The Selfish Gene" Richard Dawkins explores in depth the question of how a population dominated by one trait is vulnerable to genetic "invasion".

For any given set of traits there will be an "evolutionarily stable strategy" ESS in which the population is divided into stable proportions.

If circumstances change the "economic" advantage of one trait relative to its opposite may shift. So, the short answer is that if there were equal numbers of left-brain thinkers and right-brain thinkers then left-brain thinkers right-handed people would tend to have advantages that would enable them to propagate more effectively than the right-brain thinkers. As the population approached the ESS proportions, these advantages would diminish.

Quentin Langley, Woking The claim that left-handedness is a recessive trait will not quite do. It would imply that two left-handed parents would invariably produce left-handed offspring.

What causes some people to be left-handed, and why are fewer people left-handed than right-handed?

I had understood that there is a gene for right-handedness, in whose absence it is a matter of chance whether a child develops as left- or right-handed. This would allow any combination of parental handedness to produce offspring of either handedness.

Pelham Barton, Birmingham, UK I dont know how much truth there is in this but I was told that it was down to brain development in the womb. Left handed people had a slight starvation of oxygen to the right hand side of the brain and vice versa for right handed people.

Thus the one hemisphere of the brain became the dominant one at an early developmental stage defining 'handedness' before the hemispheres balanced out after birth.