‘Oh, that explains your creativity’ or ‘no wonder you’re good at math!’ If you’re a leftie, you might have heard such phrases directed toward you. While these claims can’t be substantiated, there are other real evidence-based benefits that being left-handed confers. For one, the distribution of brain function is more extensive in left-handers than in their right-handed counterparts. But what does this mean in our daily lives? In this article, we trace the evolution and discuss the science of handedness.
A Righteous World
In a world of right-handers, lefties have it kind of tough. And it isn’t just having to deal with the pain of using scissors and the perpetual smudging of sharpie ink. After all, ‘right’ is synonymous with correctness (you’re right!) and ‘righteous’, the moral high ground. Even in religion – the Book of Psalms reads ‘The Lord’s right hand is full of righteousness’.
Compare this with the ‘sinister’ left hand, which in many societies is reserved for toilet functions. Though less common today, many cultures enforce right-handed preference on children and not so much the other way around.
Anatomy of Left and Right
Despite the left and right hands being mirror images of each other, evidence strongly suggests some sort of asymmetry. This means that the left and right sides (hemispheres) of the brain have different functions. Sometimes the left and right ‘brains’ work together, but oftentimes, they don’t. These interesting discrepancies include both psychological and physiological processes, as we will see below.
Within our brain, it is chiefly the left hemisphere that controls logic-driven activities like reading, writing
From a handedness perspective, our left brain exerts dominance over our right hands and the opposite is also true – known as the ‘crossover’ effect.
That lefties and righties are ‘wired’ differently forms the groundwork for many studies, such as whether left-handers (right-brainers) are more creative or intelligent. Other studies have gone the other way to attempt to link left-handedness with mental illness, dyslexia and speech problems, amongst other psychological issues – with little success1.
The problem is that in left-handers, brain specialization doesn’t quite work. Some individuals have mixed specializations – such as having emotions controlled by their left brain – while others show a complete reversal of hemispheric roles!
However, it is also important to note that the brain isn’t a ‘set-and-forget’ machine. Rather, it goes through a fluid and ever-changing distribution of function. In sufferers of brain trauma, functions initially lost to damage can return in other locales of the brain—even in fully-grown adults2.
How Handedness Evolved
From a purely statistical standpoint, the chance of being a leftie or a rightie is… 50%! It makes sense that we would favor one hand over another after several years of living, but if even both choices fairly, individuals wouldn’t choose one over the other. However, only about 10% of the human population are left-handers1. The powerful bias toward right-handers is characteristic of humans (most other species don’t have this preference), so how does evolution explain this?
We can begin by looking at our closest living evolutionary ancestors. Studies show that primates favor the use of their right hands to their left when it comes to grabbing food, which tells us that handedness developed long before humans3. Further evidence to support handedness can be obtained by studying the now extinct Neanderthals. The structure of their arm and hand bones, tools uncovered, as well as ‘artwork’ found on cave walls, all point to strong right-hand dominance4.
As we evolved to perform more and more complex tasks, so too did our preference for the right hand. This is compounded by the invention and usage of tools that would have been a key driver for nature to favor handedness. After all, confining tools to a certain hand would make crafting them a more straightforward task, not to mention teaching and learning their use.
We have an explanation now for the evolution of handedness, but why the right hand over the left? Is it pure coincidence that the first tool made was picked up by a right hand? The clue lies in the structure of the brain. The left hemisphere of the brain is responsible for routine tasks, which would naturally favor the right hand, due to the direct connection via the crossover effect.
Since masting tools involved practicing (i.e. repetitive processes), the ‘routine’ left-brain/right-hand combination was more likely to be favored over the ‘creative’ right-brain/left-hand. This form of pseudo-artificial selection likely contributed to our species eventually evolving to prefer the right hand.
Real Benefits of Left-Handedness?
Left-handers can count the likes of Barack Obama, Bill Gates, Marie Curie and Leonardo da Vinci among their ranks. While it has become a social norm to label left-handers as being creative or intelligent individuals, the scientific evidence we have today is unable to back these claims. But surely, left-handedness must provide some advantages. Otherwise, the lefties in the world would have been removed from evolution! But we simply haven’t discovered what these perks might be.
A well-known study shows that left-handers have more nerve cells–an 11% increase, to be exact–that link the two hemispheres of the brain, a connection known as the corpus callosum5. Perhaps, in a right-hand dominant world, this adaptation allows left-handers to process information at a faster rate. While the corpus callosum indeed is responsible for data transfer between two sides, the tangible benefits of having a larger one remain unclear.
As mentioned earlier, left-handers tend not to follow ‘traditional’ brain specialization. This has been studied in the localization of language – the job of the left hemisphere – in aphasics, individuals with impaired speech due to brain injury.
Left-handers were less dependent on either hemisphere for language compared to right-handers, who were strongly skewed toward the left hemisphere6. This flexibility is apparent in better recovery rates in left-handed individuals who have suffered an injury to either hemisphere.
It seems that although significant differences exist between left and right-handers, their subtleties lie beyond what we understand with today’s evidence. A combination of genetic and environmental factors comes into play when deciding your handedness, which is, in fact, on a spectrum of weak to strong. Handedness, in turn, influences brain structure and indeed, the way we function.
But for now, we lefties can continue to benefit by blaming our terrible handwriting on, well, just being born this way.
Reference
- Hardyck, C., & Petrinovich, L. F. (1977). Left-handedness. Psychological
bulletin , 84(3), 385. - Su, Y. S., Veeravagu, A., & Grant, G. (2016). Neuroplasticity after Traumatic Brain Injury.
- MacNeilage, P. F., Rogers, L. J., & Vallortigara, G. (2009). Origins of the left & right brain. Scientific American, 301(1), 60-67.
- Cashmore, L., Uomini, N., & Chapelain, A. (2008). The evolution of handedness in humans and great apes: a review and current issues. J Anthropol Sci, 86, 7-35.
- Witelson, S. F. (1985). The brain connection: the corpus callosum is larger in left-handers. Science, 229(4714), 665-668.
- Goodglass, H., & Quadfasel, F. A. (1954). Language laterality in left-handed aphasics. Brain, 77(4), 521-548.
About the Author
Sean is a consultant for clients in the pharmaceutical industry and is an associate lecturer at La Trobe University, where unfortunate undergrads are subject to his ramblings on chemistry and pharmacology.
