In detail

Why are we left or right handed?

Why are we left or right handed?

Are we born or do we become right or left handed? It is said that between 85% and 90% of the world's population corresponds to right-handed people; There are many myths and interesting questions about the laterality of people, many of these questions are being answered thanks to the neurosciences, the understanding of hemispheric asymmetries changed.


  • 1 Laterality and spinal cord
  • 2 What does epigenetics have to do with being left or right handed?
  • 3 Laterality and curiosities

Laterality and spinal cord

Why is it that we are right or left handed? For a long time it was thought that laterality was determined by the brain, however, The asymmetry in the spinal cord gene expression is manifested from the first weeks of gestation of the baby in the womb of the mother. A study conducted at the University of Ruhr from Bochum, Germany by Sebastian Ocklenburg and collaborators from different countries (2017), found that the preference for using the right or left hand may originate in the spinal cord, they say that it is who determines if we use more one or the other hand.

Investigators they studied gene expression in the spinal cord between the eighth and twelfth week of gestation, they observed that in the eighth week, there were already marked differences in the left part and the right part of the spinal cord segments and that it is she who transmits electrical impulses to control the movements of upper and lower limbs (arms and legs) in initial stages.

This activity is carried out long before the part of the brain responsible for the movement, the motor cortex, is "connected" to the spine. The asymmetry will define if the person will be right or left handed between the eighth and ninth week of gestation in the womb of the mother. Weeks later, the differences in each hemisphere in terms of shape and size also become visible.

Ocklenburg and his collaborators (2017), found that the spinal cord and cerebral cortex are not communicated in such early stages of pregnancy, so they concluded that laterality is determined directly by the spinal cord and not by the brain as was thought a few years ago. Regarding hemispheric asymmetries, the data suggests a spinal, not cortical, start, they said.

They observed that the movements are controlled by means of the spinal cord, which gives the order to the cerebral cortex to execute a movement, while being able to detect certain environmental changes.

What does epigenetics have to do with being left-handed or right-handed?

The epigenetics It is a regulation system that controls the expression of genes without affecting their composition, corresponds to the study of the interactions between genes and the environment in which they occur in organisms.

Some genes may or may not express themselves, this also depends on environmental influences, In the case of the spinal cord, these influences affect it in different ways. Genetic analysis showed that the left and right side of the spinal cord develop at different rates. Even if  It is worth mentioning that genes can only be a component of laterality.

"Before the eighth week of gestation, the cerebral cortex and spinal cord are not yet communicated, towards the ninth week of gestation and through the spinal cord is that it begins to have a predominance of a certain side."

Laterality and curiosities

Right hemisphere and pessimism

A study by David Hecht (2013) found that left-handed people could be more prone to depression and negative emotions, since they observed that the right cerebral hemisphere of left-handed people is activated more regularly and this has recently been associated with various characteristics of pessimistic people.

You may be interested: Characteristics of pessimists

Lefties and language

most of right-handed people process language in the left hemisphere, left-handed people have a distribution of this ability in both hemispheres. Which leads them to have more random and less specific skills, so if a left-handed person has a lesion in the left cerebral hemisphere, which is where language is processed, they tend to recover more quickly, since their processing skills of language are scattered in both hemispheres, having distributed language skills in both hemispheres makes the neuronal system more complex, so may increase susceptibility to abnormalities and neurodevelopmental disorders, as Daniel Geschwind, professor of psychiatry, neurology and human genetics at the University of California, Los Angeles, U.S.A.

Increasingly specialized studies on human development from such early stages could help identify new indicators that allow intervention at early stages and try to compensate for any development problems as soon as possible.