As children get older, they tend to start using one hand for certain tasks, such as spelling or drawing. Childhood dominance of one hand is generally classified as right, left, or mixed, and tends to subside around the same time they begin to speak - around four years of age.
We now know that the dominance of one of the hands of a child tells us about the organization and function of their brain. The left and right hemispheres of the brain control the motor systems on opposite sides of the body. However, the left and right halves of the brain are not equal in their control of various types of behavior, which leads to the dominance of one side over the other to perform certain tasks. The dominance of one hemisphere over the other for a particular behavior is called cerebral laterization.
Scientists believe there are clear reasons for the evolution of cerebral lateritization. First, one control hemisphere controls the process of reducing the likelihood of both hemispheres to control the response. It also allows various processes, such as language and attention, to work in parallel on two hemispheres.
For the vast majority of people, the left hemisphere of the brain is dominant and is used to transmit speech. And the same area of the left hemisphere that controls speech controls the actions of the hands.
As a result, most of the world's population (about 90%) uses their right hand when they use tools such as pens or when they gesture. Evolutionary psychologists suggest that the use of tools and gestures played an important role in the development of human speech. One theory suggests that since sight is our primary sense, human communication first manifested itself in gestures. As soon as we became expert users of the tools to free our hands to use them, our communication began to be transmitted by speech. The structured sequences of manual steps required to make and use tools also prepared the brain for language syntax.
In order to acquire complex skills such as speech, children must first develop basic sensory and motor abilities.
Until the middle of the 20th century, scientists believed that left-handedness was a developmental defect. It has been associated with a range of developmental disabilities, ranging from language deficits to mental disorders. In fact, many left-handed children of this era were forced to write with their right hand in an attempt to "retrain" them. Today we understand that dominance of one hand is not a binary characteristic (left or right), but rather, it exists along a gradient that ranges from more left-handed or more right-handed.
As children begin to develop their motor skills, they can use both the left and right hand equally for simple actions. This is because both hands can complete the task with ease. However, for the majority of the population, more complex tasks require specialized technological properties of the left hemisphere of the brain. For example, most children choose their right hand for writing.
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Recent research suggests that children who use their right or left hand consistently also have good brain laterization and typical language production. On the other hand, mixed use of hands is associated with atypical development of motor and language abilities.