Scientists acknowledge that half the animal kingdom is right-handed and the other half is left-handed.
In humans, the assessment of laterality is complex, as one must consider in addition to the dominant hand, the dominant eye, ear, shoulder, pelvis, leg and foot. This is called the governing organ which one spontaneously uses to carry out a task. Lateralization is basically a clever adaptation of the body that automatically chooses which hand, foot, eye, ear is more efficient and practical to use. There are people who have complete or incomplete lateralization. In other words one may be right-handed and right-eyed and left-footed and left-legged. This is an example of incomplete or weak lateralization (cross or mixed) which can be useful for certain activities and a hindrance to others.
Most people dependent on the left hemisphere for language, mathematics, logic, analysis, while the right provides the perception of space, sound and music, synthesis, “Gestalt.” Both work in a complementary manner.
Neurologists have determined that in a small percentage of the population, approximately 5%, their language centers are located in the right hemisphere. Through applied kinesiology and muscle testing not only has this fact been confirmed but it seems that this reverse hemispheric dominance is much more widespread than one might think. For this reason it is not only important to determine brain dominance, but also whether the dominant hemisphere is verbal/analytical or Gestalt/synthetic.
Lateralization has always existed in mankind since ancient times. In fact, prehistoric man was lateralized and this corresponded to the hand that was not working. Since the beginning, the prevalence was the left hemisphere. However, the left hemisphere has a more recent history than the right: it has only 5000 years of technical and mathematical reasoning, while the right has experienced approximately 600 thousand years of instinctuality.
From the beginning three-fourths of infants start to walk automatically by advancing with the right foot. Even the rotation of the head in infants is prevalent to the right. Instead manual laterality appears at about eight months and is refined later. In the second year lateralization of language is established which is dominant, as we have seen, in the left hemisphere. Lateralization is completed between 14 years and 21 years of age in parallel with the complete development of the various energy centers.
Left laterality may be advantageous in certain cases; for example in certain sports such as duelling being left-handed is an advantage, because as the left hand is controlled by the right hemisphere it directly has perceptual-spatial cognition, while the right hand has to send the information from the left hemisphere to the right to obtain the same result. The two hemispheres are in fact connected by nearly 2 million fibers that form the corpus callosum. According to a Canadian study interhemispheric fibers would be more numerous in left-handers compared to the right-handed.
Weak or crossed laterality can be useful in certain circumstances, while it can cause problems in other situations. For example, left-eye laterality with right-hand laterality is very useful in tennis.
Weak or crossed laterality can be perfectly compensated in the first half of life, while in the second half it can determine subliminal chronic stress responsible for inflammaging and therefore an acceleration in the processes of physical and brain aging.