Why Am I Left-Handed? Blame Tubulin Proteins for This Asymmetric Brain Twist

My family is predominantly left-handed. Of four brothers born to my parents, three of us write and do most things with our left hand. My father lived at a time when lefties were forced right by teachers. Left-handedness has always been associated with dark forces. In Latin, left is sinistra from which the word sinister is derived. In some Muslim societies, left-handedness is discouraged even though writing in Arabic (from right to left) is much easier if you are a leftie. That same advantage exists for lefties when writing the Hebrew alphabet.

A quick look at languages notes that 12 including Arabic and Hebrew are right-to-left written. These include Aramaic, Azeri, Divehi, Fula, Kurdish, N’ko, Persian, Rohingya, Syriac and Urdu. I often wonder if the inventors of these alphabets were left-handed which facilitated ease in writing them?

What determines whether you are born left-hand or right-hand dominant? An article appearing on April 2, 2024, in Nature Communications, describes a study by neuroscientists at MSH Medical School Hamburg in Germany that identified the genetic origins of handedness in humans implicating a specific group of proteins called tubulins. Tubulins are the proteins that build the skeleton.

Handedness has been studied because of its relationship with written languages. Left-handedness is also studied because it has been linked with several neurodevelopmental disorders including schizophrenia and bipolarism. In humans, 10% of us are left-hand dominant. Left-handedness is more predominant in males than in females. Left-hand dominance over right-hand is not seen as a predisposition for those who exhibit ambidexterity although it was often thought to be the case. The likely error in this belief comes from past behaviour to force left-handed people to use their right hand as happened to my father.

The Hamburg study points to tubulin proteins as determining left-right brain asymmetry. It notes that at the embryonic stage of human development, the brain hemispheres become wired differently determining many innate behaviours including:

• which side of the mouth we use to chew food.
• the predisposition to lean when hugging someone.
• which hand is dominant.

A previous study in the United Kingdom pointed to 48 genetic variants in non-coding DNA regions associated with left-hand dominance. These areas of DNA contain the genes that control tubulins, a group of proteins with a tube-like appearance. One of these tubulins called TUBB4B is 2.7 times more common in people exhibiting left-hand dominance.

Why do tubulins cause some of us to write with our left hand versus our right? The theory described in the Nature Communications article points to how tubulins affect the hair-like protrusions in cell membranes called cilia. These hairs direct the flow of fluids in the developing embryo and in a small number of cases produce brain asymmetry variations. If unfamiliar with the term “brain asymmetry,” it refers to the two halves or hemispheres in the the brain that often perform very different functions. The Hamburg researchers call molecular handedness an “asymmetric twist” that occurs during early brain development.

This latest twist on handedness counters the preconceived notion supported by a 2009 published study appearing in Neuropsychologia which studied 30,161 U.S. adults and concluded that common and unique environmental effects to hand preference were likely the determining factor in left versus right-handedness and not genetic factors.