What determines handedness?
- Selin Gorkem
- Mar 24, 2021
- 4 min read
Albert Einstein, Marie Curie, Leonardo da Vinci: what do these individuals all have in common? Other than being revolutionary figures who have shaped society as it is now, they were once all a part of the 10% of the world who are left-handed.
We all know someone who’s left-handed, whether it’s your best friend, a parent or a neighbour, and if you’re lucky enough, it could even be you. However, it’s interesting as to why left-handed people are a minority in the world, and why the right handers are dominating the world of writing. It’s useful to think about when this is determined, whether it's genetic or learned from the environment an infant is raised in.
Why do people have a preference?
Hand preference can normally be observed from infanthood in humans however many research shows how it could have developed since gestation in the mother’s womb. Using one dominant hand helps to differentiate between the different parts of the body, where the left side is controlled by the right hemisphere and vice versa. Having a hand preference can be very useful in the sense that we can put all of our energy, focus and attention into perfecting fine motor skills on one side to write in a more accurate way and to text, chop up food or even sew as precisely as we should. It may have been an evolutionary trait, in which early humans would have needed good precision in order to kill their prey to survive, and having developed hand-eye coordination and hand control would have vastly enabled them to have meticulously hunted their dinner.
A trait of the homo sapiens is that they have had a dominant hand since the start - enabling them to use weapons in a much more efficient way to kill their prey to survive. Other animals have a 50-50 distribution of right to left-handedness, suggesting that this could have been a form of cognitive evolution, making us much more unique than other mammals.
Why is right the 'right way?
So you may be wondering, unlike other animals, why don't humans have a more even spread of which hands they use a species? The answer may lie in the functions of the different hemispheres in the brain and the specific functions they are adapted to carrying out. The right side of our bodies, including our hands, are fully coordinated by the left hemisphere of our brains. Although it is not fully confirmed by science, there are multiple theories linked to the left side of the brain being involved with more cognitive and intellectual functions in comparison to its fellow hemisphere.
For apes and other chimpanzee or gorilla species, there are no preferences in terms of which hand they use; they simply alternate it, as there is no real survival advantage to being able to use their hands. As early humans started to walk more upright, they found that their hands were free and gave them an advantage over other species; they could attack and run to/away from their prey simultaneously. They needed to learn how to use logic and intellect such as their tool skills (controlled by the left hemisphere) while being aware of their surroundings and being able to recognise foreign and familiar faces as a survival technique (controlled by the left hemisphere). Therefore, the most efficient part of the brain for this multitasking would be to utilise each hemisphere for what it's good for; hence why there is a right-handedness bias in society: it could be argued that is it a key feature of human evolution we can observe to this day.
What leads to people being left-handed?
Geneticists are certain that genes play a part in determining whether our left or right side of the brain controls our writing - however, the struggle is to exactly determine which combinations of genes since as of right now there is a list of 40 possible genes. These genes when they come together could also determine other parts of the non-symmetrical human body and the other, different things either hemisphere may control. Although there is just solely a chance of random mutation and variation within the human species or specific genes that could affect the handedness of sufferers with conditions like schizophrenia or autism, there could be a possibility of environmental factors.
A study in the Netherlands suggested that birthweight had a significant correlation with the handedness of an individual as a major environmental factor. If a child was born prematurely or as multiple births, the chances of them being lefthanded was much higher, suggesting a theory that these could have altered brain activity within the crucial development stages in newborn babies. Although these differences don't make left-handed people any disadvantaged than right-handed people physiologically, some may argue that a shorter life span and increased risk of ADHD and other mental disorders may be at stake, however, there is not enough conducive or biological evidence to back these claims.
Even if left-handed people experience many 'annoying in the moment' but insignificant problems in their daily lives, such as not being able to use scissors properly, their ink pens smudging as they try to scribble down their thoughts down on a page and using can openers, they are quite the unique and lucky bunch of people within society. Their brains work and have been adapted in a way like no other, allowing researchers the opportunity to delve deeper and look into how the brain functions for different people and the genetic/environmental reasons contributing to it.
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