DATES

06/03/2017

Between 10% and 15% of the population (figures vary depending on the statistics we consult) is left-handed. Its existence is not determined by race, sex or geographical location: perhaps you are, or your father or your partner. The halo of mystery that surrounds those who write with the left hand has linked them with painting, music and introversion, myths that science has been in charge of erasing in its path. The explanation of why some people show dexterity with one hand (or one foot) and the rest with the opposite, or both, until now seemed an enigma. Although it was related for a long time to the result of the activity that registered the right or left hemisphere of the brain during the development of the fetus, a new study has dismissed this cause and solved the mystery.

Researchers at the Ruhr University in Bochum (Germany) point out in an article published in the eLife magazine that although this ability does develop in the womb, it is not the brain but the spinal cord. The scientists detected that at eight weeks of gestation there are already marked genetic differences between left and right-handed. The expression of certain genes of the spinal cord, responsible for controlling the movement of the legs and arms is different for each of these groups.

Since the 1980s, it has been known that "the preference to use either hand develops in the uterus and in the eighth week of pregnancy. From the thirteenth, they choose to suck the right or left thumb, "the researchers say. The movements of the extremities of children are controlled by the spinal cord, which orders a movement with instructions from the cerebral cortex: however, and here comes the finding, these two parts of the body are not communicated in such early stages of the Gestation, so the researchers conclude that being left-handed or right-handed is determined directly by the spinal cord.

Why are we different?

But this still does not explain why we use one side of our body and the other the opposite: by tracking the cause of this asymmetry, experts have found that the preference for using the left or right hand is not written from the beginning in DNA , But depends on environmental factors (yet to be determined) produced during pregnancy. That is, epigenetics influences: DNA is a chain of genes in which some are expressed and others are not, depending, in many cases, external stimuli. The explanation of laterality, according to experts, would be in how "these environmental influences differently affect the left or right spinal cord".