Why Do People Have Dominant Hands?

There isn’t usually a consensus in the medical or research community when it comes to understanding why most people have a dominant hand. One of the more popular theories assumes that the brain engages in something of a division of labor, assigning dominance to one hand over the other in order to promote efficiency; this is usually consistent with the idea of each of the brain’s hemispheres controlling a different sort of data and information processing. Another theory posits that dominance is really a matter of perspective, and that the hand best at fine motor skills may actually depend on the gross motor and “helper” qualities of the other in order to fully function. Some researchers are also exploring whether dominance is simply a matter of genetics. What most scholars do agree on, though, is that the brain signals that lead to dominance, no matter why they happen, seem to be related to learning and information processing generally. Understanding dominance may help uncover things like why people have learning disabilities.

When people talk about dominance in hands, they’re usually referring to what is known more casually as “handedness,” or the idea that most people have one hand that is used to do things like write or grab for objects more instinctively than the other. The majority of humans are “right handed,” which means that their right hand is dominant and the one they use for the majority of daily tasks.

The next most common is left handedness, which as much as 10% of the population is thought to be. Then come the alternatives. Mixed handedness is when some individuals will use their right hand for one activity, like writing, but their left for another, like holding scissors or hitting a tennis ball. Finally, there is ambidexterity, which is usually acknowledged as very rare. Being truly ambidextrous means that both hands are used equally for all activities. The flip side of ambidexterity is ambilevous or ambisinister qualities, which cause a person to be equally poor when using either hand.

The most commonly accepted theory explaining dominance is division of labor. This refers to the hemispheres of the brain and how information is processed and divided between the hemispheres and fine motor skills in the hands, eyes, feet, and ears. It's generally known that speaking and communication activities in right handed people are performed in the left hemisphere of the brain. The major argument against this theory holds that what's true of right handed people should be opposite for left handed people. In other words, left-handed people should process language in the right hemisphere of their brain. That isn’t usually the case, which makes this theory flawed, at least from a technical perspective.

Another suggestion is that dominance happens as a result of both hands working together. This is called bilateral coordination. On this theory the dominant hand is a “worker hand” that performs most of the fine motor skills required to get through a day. The non-dominant hand is thought of as the “helper hand” and performs gross motor skills like stabilizing objects.

In 2007, scientists looking for a left handedness gene found a marker later named LRRTM1. This gene gives some credibility to the thought that handedness might be genetic. The genetic predisposition theory is also being tested for validity because the gene carries other traits as well. Even sill, the connection isn’t apparent. Only about a 1 in 4 babies born to two left handed parents are also left handed. The gene may be recessive, as is the case with the gene determining light eyes, but not enough is known at this point to say for sure.

Dominance when it comes to hand use might not seem like such an important thing when doing ordinary tasks like writing a check for the groceries, but the implications may go pretty deep. Scientists increasingly believe that there is a relationship between learning and handedness. Finding answers to dominant hands could unlock seemingly unrelated issues like dyslexia and stuttering.