Why are we born left-handed? The answer at hand…

Why are we born left-handed?  The answer at hand...

On August 13, we celebrate International Left-Handers Day. The opportunity to talk about 15% of French people who are part of this “club” and their characteristics. But besides, why are they so few? The question is regularly studied.

They write with their left hand, kick a ball with their left foot or read primarily with their left eye. Left-handed people, who make up around 15% of the French population, remain mysterious: why are they different? Where does this “loss rate” (wearing out the left side) come from? We looked for the reason.

Being left-handed, what does it mean?

Unlike right-handed people, a left-handed person has more developed the right hemisphere of his brain which governs the entire left side of his body (the right side is governed by the left hemisphere). Left-handedness is thus more often defined by the writing hand, which is the most common action, but not only. One can therefore also be left-handed in foot, eye, ear…

We then speak of true left-handers, homogeneous, completely lateralized to the left in their visual, auditory, manual and pedestrian functions. And this is not a handicap, it is simply a fact, but which can sometimes be annoying: the world, made mainly for right-handed people, is not always suitable for them.

Why are we left-handed?

But what makes a child a child born left-handed or right-handed? Why this lateralization? Researchers are scrambling to provide an answer… but for now, they have only been able to put forward hypotheses.

  • Some studies suggest a genetic hypothesis. Indeed, when both parents are right-handed, the proportion of left-handed children is then low (about 9%). But when one of the two parents is left-handed, then the proportion increases (between 16 and 20%), and even more (about 27%) if both parents are left-handed;
  • Others think that the environment in which the child grows up has a role… Hypothesis which can be heard but also decried. Indeed, in countries where left-handed people, frowned upon, were forced to use their right hand to write in particular, the number of left-handed people has decreased… Only to rise once social pressure has disappeared;
  • The position taken by the fetus in the womb of the mother is also evoked, in particular the position of the head. As the mother’s uterus expands more to the right, the fetus sits there in a certain way, head down, back to the left, giving more room to the right arm, than the fetus gets used to using more than the left;
  • Hormone levels are also studied: during fetal life, this could influence the maturation of the brain and, in the majority of cases, reinforce the role of the left brain… and therefore of the right hand.

In the end, it is difficult to answer this question clearly: the explanation is probably multiple: genetic predispositions, influenced by fetal life and the environment in which the child develops… or other factors that we don’t know yet! Lefties remain a mystery!