Human Anatomy and Physiology

Why do some people write with their right hand and others with their left. What makes one choose their hand?



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The human brain is a symmetrical structure with an axis of symmetry running vertically in a plane that goes up the nose and between the eyes. This means that the brain has two halves and the right hand half controls the left side of the body and the left hand half controls the right side of the body.

While the two halves of the brain look similar and look after the opposite sides of the body, in detail some of the cognitive functions are not split equally between the two halves and reside on one side or the other. This results in one side of the brain being apparently dominant over the other.

People who are right handed have the left side of their brain dominant, while the opposite is true for left-handers.

Thus the choice of hand is dependent on brain structure and is thought to be genetically inherited (over 90% of the adult population is right handed). There is also some evidence that left-handers' brains are structured differently in a way that widens their range of abilities and this is why the left handed trait remains in the human gene pool.