Handedness

Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is said to be right-handed, and one who is more skilled with the left is said to be left-handed.

Definition

Handedness is not a discrete variable (right or left), but a continuous one that can be expressed at levels between strongly left-handed and strongly right-handed. There are four types of handedness: left-handedness, right-handedness, mixed-handedness, and ambidexterity. Mixed-handedness is the change of hand preference between tasks. Ambidexterity is extremely rare, although it can be learned. A truly ambidextrous person is able to do any task equally well with either hand. Those who learn it still tend to sway towards their originally dominant hand.

Development

Hand preference develops in early childhood and is likely to be genetic. It is determined by prenatal hormonal activity, which also shapes the development of other parts of the brain. For example, testosterone suppresses the growth of the left hemisphere and promotes growth in the right, leading to a preference for the right hand.

Implications

Handedness has implications in life. For example, left-handed people are more likely to develop schizophrenia and other mental disorders. They are also more likely to suffer from dyslexia and attention deficit hyperactivity disorder (ADHD). However, left-handed people may have an advantage in sports and other activities that require spatial skills, as they use the right hemisphere of the brain, which is involved in spatial reasoning.

See also

• Ambidexterity
• Mixed-handedness
• Schizophrenia
• Dyslexia
• Attention deficit hyperactivity disorder

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