Being right or left handed is not the result of chance or habits that we establish since childhood, but it is the consequence of a process of evolution of the nervous system, a process that occurs when we grow and that is necessary to raise the degree of functional complexity of the brain.
Apart from this neurological explanation, which indicates that the right cerebral hemisphere predominates in the right-handed and the right-handed in the left-handed, the reason for one or the other predominance is still unknown. And on the subject there are varied theories.
The genes and the environment
In the beginning, being a right-handed or left-handed person would depend on two factors according to different currents and studies: the inheritance and training or experience that each child has during their cerebral maturation.
However, most researchers take distance from these extreme positions and point out that the laterality of the person is influenced by both genetic and environmental factors.
In addition, remember that we are not born right or left handed, but we are becoming such in our early childhood.
According to the genetic position, we see that the predominance of one or more laterality is something that is conditioned by our genes, so we would be more likely to be left-handed if there were a family history.
A theory elaborated by geneticists of the National Cancer Institute of the United States raised the hypothesis that most people have a dominant gene that makes them be right-handed. On the contrary, 20% of people lack this gene, so they have a random chance of being right or left handed (50%). For Klar, the presence or absence of this gene corresponds to a conventional genetic condition, such as that which determines the color of the eyes or baldness.
A group of researchers from the University of Oxford discovered, in August 2007, that the LRRTM1 gene is crucial for a person to be left-handed.
Other psychologists believe that laterality has to do with environmental factors and depends on the children's learning of their parents, the influence of the school or the habits instilled by their relatives.
More theories to explain why we are left handed
In addition, there are other theories which could explain that a child is right-handed or left-handed regardless of genetics or the environment, although it refers to more specific cases (such as injuries in one hand that eventually lead to the domain of the other for skills):
Excess testosterone: a high level of the male hormone, testosterone, prenatal could predispose to the development of a left-handed subject, according to one of the studies included in the I Spanish Congress of Psychobiology (University of Oviedo). Another theory says that exposure to high doses of testosterone before birth can induce left-handedness. The abundance of testosterone, which is usually much higher in men than in women, would cause more left-handed men.
Birth stress: lesions in a baby's cerebral hemisphere, during pregnancy or the first months of life, can induce one of them to develop further, in the case that the injured left hemisphere is supposed to develop left-handedness.
Differences in the right and left handed brain
In what there is conformity, as we have pointed out at the beginning, is that the causes of being right or left handed are neurological, that is, it is determined by the brain and depends on the "laterality" of the person.
Laterality is a motor predominance related to body parts, which integrate its right and left halves. The laterality is reflected in the fact that one of the sides of our body predominates over the other in the performance of most activities: left-handers have left laterality, right-handed.
In the brain there are two hemispheres: the right, which directs the movements of the left side of the body, and the left, which governs the movements of the right side. Almost always its left part is the dominant one, so most orders are destined to the right of the body.
But left-handed people are the exception, since the opposite happens in them: it dominates the right hemisphere that is the one that directs the left side, so it is on this side that it commands.
According to some research, it could be that the predominance of right-handed people (between 8% and 15% of the world's population is left-handed) is due to the fact that brain functions housed in the left hemisphere are more important and therefore dominant. Although current theories doubt that the role played by the right hemisphere (related to creativity and ingenuity) are secondary.
When we talk about hemispheres, we should not consider them opposite hemispheres: they are complementary and there is no hemisphere more important than the other.
So that they remain many unknowns to solve about why we are right or left handed. Be it more for inheritance, be it for the environment, I think that what matters most to parents is to know if the little ones are right-handed or left-handed at the right time, beyond two years of age, with the purpose of helping them to develop in your daily tasks.
