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21/08/2019

PHILOGENIA AND ONTOGENIA

Anaxagoras and Aristotle were right when they said: "Man is intelligent because he has hands" and "Man has hands because he is intelligent."

Phylogenetic and ontogenetically the hands are consistent with the bipedal position that allowed the conquest of the planet: tools, weapons, vehicles, forms of communication, that is, everything has depended on coordinating brain and hands.

* General and Child Psychiatrist, Faculty of Medicine, Technological University of Pereira, Mental Hospital

The child "manipulates" the world: touch, caress, explore his body and what

surrounds, sucks his fingers, sculpts and takes (1). The use of the right or left hand,

or the ability to be right or left handed, is a matter of degree. In all societies there have been left-handers, but all have had the tendency to be right-handed. Numerous socio-anthropological studies have also shown that ancient cultures, even extinct ones, were right-handed. Dextrality that could not be explained, nor why the dominance of the left cerebral hemisphere is more common (even in most left-handed ).

The cave paintings show human faces with the gaze directed to the left (artistic tendency of the right-handers to draw facial profiles to the left. These same

Primitive paintings show human figures holding utensils and weapons in their right hands.

We share with chimpanzees the characteristic of being the only mammals to have a dominant hand.

LATERALIZATION AND CEREBRAL HEMISPHERIC DOMINANCE

From three to four years of age a lateral preference begins to appear in the human being that is completed around eight years to take us to the percentage statistics of 64 pure right-handed, 32 ambidextrous and only 4 pure left-handed. That is, only 4% of humanity is totally left-handed <2).

The lateralization is not always homogeneous (eye, ear, hand and foot), but it can be heterogeneous, that is, it can have combined lateralizations. The diagnosis of lateralization is made by applying batteries of psychological and mediating tests

the observation of the functioning of eyes, ears, hands, arms, legs and feet.

There are simple tests such as seeing through a monocle, hearing the ticking of a clock, cutting with scissors, crossing hands and arms, clapping, crossing your feet, putting on pants, kicking, jumping,

kneel down. These tests show the preference of using right or left organs or limbs (3).

The dominant cerebral hemisphere is of greater size and weight. In most human beings, including left-handers, the left is the dominant hemisphere. The left hemisphere is logical, symbolic, mathematical, verbal, analytical, abstract, reasoning; predominates in language. It processes the right eye and ear information and governs the

motor activity of the right hemisphere (4) <5).

The right hemisphere, dominant in some lefties, is instead spatial, intuitive, nonverbal, synthetic, emotional, musical, concrete, artistic; predominates in visual functions and

motor It processes the information of the left eye and ear and governs the motor activity of the left hemibody (4) (5).

In explorations with «dichotic listening» (in which simultaneous information is provided for both ears) it has been found that the right ear (left hemisphere) perceives

better syllables, words and figures while the left ear (right hemisphere) captures better melodies and noises.

Rev Colomb Psiquiatr Vol. XXVIII, No. 2, 1999

The left-handed world

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