Are You Only Left Handed By Chance?

Are you only left handed by chance?

Nearly nine out of ten people are right-handed. This means that only 10% of people around the world are left-handed. Why is that? Is it luck? Or is right-handedness genetic? Does it come with practice? Can I become left-handed? Does it depend on my personality?

Well, the explanation is not that simple. A lot of research has been done but there are no definitive results. However, there are two hypotheses with more scientific support.

For both explanations , right-handedness or left-handedness is neurological. That is, it is the result of how our nervous system evolves. Therefore, we know with certainty that we were not born this way. Nor is it coincidental. On the contrary, it develops in childhood. But why?

Left-handed or right-handed? The brain is responsible

This first theory has been around for years. It says that your left or right handedness comes from your brain. It is determined by the ‘laterality’ of the person. Laterality means whether you use the right side or the left side of the symmetrical parts of the body more: hands, eyes, feet, ears…

left-handed brain

Anatomically, our body parts are symmetrical. But on a functional level they are asymmetrical. It is laterality when one side of the body dominates the other when doing things (writing, opening doors, playing tennis…). Left-handers use the left side and right-handers naturally use the right side.

We develop laterality between three and six years of age and it is fully formed by the age of seven. If the child has not yet developed this by the age of five, you should consult a specialist.


To understand the theory we just introduced, we need to explain what lateralization is. It means that one hemisphere in us is more dominant. In general , the right hemisphere ‘steers’ the movements of the left side of the body. And vice versa, the left hemisphere ‘steers’ the movements on the right side. That’s why we can say that:

  • Right-handed people have left hemisphere dominance and right laterality.
  • Left-handed people have right hemisphere dominance and left laterality.

The spine determines everything

Recently, researchers from the Ruhr University of Bochum (Germany) said that the brain does not choose laterality, but rather the spine. They found that at eight weeks of pregnancy there are already clear genetic differences between left-handed and right-handed babies.

That is, even when the baby is in the womb, the genes in the spine responsible for controlling limb movement have already divided into several groups. For example, babies already choose to suck their thumbs on only one side. So how is this possible?

The process works as follows. The cerebral cortex sends motor commands to the spine, which controls the movements of the child’s legs and arms. The researchers found that at eight months of age, there is still no communication between the cerebral cortex and the medulla (the medulla oblongata). So only the spine can be responsible for their movements.

For these researchers, epigenetics explains laterality. This means that the environment affects genes, and these affect the left and right sides of the spine differently.

left-handed child

What about people who are ambidextrous?

If you’re neither right-handed or left-handed, your laterality probably isn’t developed correctly. When this happens, children may be ambidextrous or have crossed or contradictory laterality.

  • Being ambidextrous means you have undefined laterality. In other words, there is no dominant hemisphere of the brain. Therefore, the child uses both symmetrical parts of the body interchangeably. They can perform activities with both the right and the left side.
  • Crossed or mixed laterality is when the lateralities are interchanged. For example, Spanish tennis player Rafael Nadal’s right eye is his dominant eye, but his left hand is dominant.
  • Contradictory laterality happens when children change their laterality. Usually this happens when a left-handed child is forced to write with the right hand. They then use their ‘natural’ hand only in activities that are not mediated by culture, such as brushing teeth, greeting or pushing something.

Contradictory laterality is related to the marginalization of left-handed people. We even see it in our language. Having two left hands means being clumsy. In fact, in many countries, such as in China, someone who uses their left hand is looked down upon and children are corrected.

There are still many uncertainties in figuring out how we become right-handed or left-handed. However, research on the brain and spine brings us closer to an irrefutable scientific explanation. 

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