August 13 marks the essential International Left-Handers Day, honoring those who favor their left hand for a myriad of tasks. Making up approximately one in ten of the global population, left-handers, often described as a "minority", have been gaining ground since the 20th century, sparking increasing intrigue. Researchers, in their relentless pursuit to unravel the mysteries behind right-hand dominance, have yet to secure definitive answers. However, one thing we know for certain is that our collective inclination towards the right hand sets us apart distinctively in the animal kingdom.

Scientists, fervently delving into the study of this hand preference, converge on a fundamental idea: the leaning towards the right hand has roots deeply embedded in biology and even genetics, accounting for at least 25% of observed cases. Yet, chance also plays its part. Two leading genetic theories discuss the impact of evolutionary natural selection, where the control of linguistic functions and speech predominantly occurs in the left frontal lobe of the brain. Given this lobe also manages the motility of the right hand, millennia of evolution have crafted a "genetically-biased" legacy favoring left-right asymmetry. Thus, nearly 98% of right-handers harness the left side of their brain, while this figure stands at 70% for left-handers.

These theories shed intriguing light on two distinct alleles - these variants or alternative forms of a gene or genetic location, typically linked through genetic relationships. One of them, the "D gene", is pervasive in humans, acting as a cornerstone of individual genetic heritage, dictating the majority preference for the right hand. In contrast, the "C gene" assumes a more marginal stance, injecting a degree of unpredictability into the preferential equation. Individuals carrying this alternative allele have an increased 50% likelihood of aligning with the left-hander cause.

Fascinating Insights from Functional MRI: Left-Handers Light Up Differently

The remarkable findings from functional magnetic resonance imaging (fMRI) offer no shortage of intrigue. When right-handed participants whisper words, only 4% of them engage both brain hemispheres. However, when a similar task is presented to a group of left-handers, nearly 10% of them activate the right brain pathway. The overwhelming majority, though, process speech in the left lobe of the brain, much like their right-handed counterparts.

Let's delve deeper into these intriguing facts: In the womb, fetuses carried by women undergoing psychological stress appear more inclined to touch their face with their left hand. Simultaneously, a higher frequency of left-handedness emerges, especially among twins. Yet, a study conducted a few years ago by Yale University adds layers to this intricate canvas: left-handers tend to exhibit a higher propensity for mental disorders, dyslexia, and attention deficit hyperactivity disorder (ADHD). Moreover, a 2007 study in the British Journal of Cancer pointed to an increased predisposition for breast cancer, particularly post-menopause, suggesting a potential disturbance triggered during initial fetal growth phases.

Yet, counteracting research infuses ambiguity into these conclusions. Some scholars challenge the significant impact of hand preference on individuals' health and lives. In fact, being left-handed could correlate with superior linguistic abilities and a reduced risk of Parkinson's disease, according to a 2019 study in the journal Brain. The foundations of this analysis rest on an exhaustive exploration of thousands of left-handers' brain scans and genomic analyses of hundreds of thousands of subjects, aiming to dissect the woven links between genes, brains, and hands.

A historical rewind is in order, plunging us into theories once positing the left hand's supremacy on the battlefield. The proposed scenario hinges on the notion that most men, historically blessed with privileged access to resources and reproductive opportunities, had a subtle inclination towards left-handedness. However, the "fighting theory" isn't immune to critiques. Observations suggest that the potentially fragile health of left-handers and their slightly reduced life expectancy haven't been solidly proven in most pertinent studies.

In this vein, a recent study, collaboratively conducted by researchers from Lund University in Sweden and the University of Chester in the UK this year, challenges these established notions. These innovative minds subjected the "fighting theory" to an update in line with current knowledge, advocating in the journal Symmetry for right-handers' dominance on battlefields throughout human history, accounting for their numerical superiority.

According to this group of researchers, this combat advantage stems from two factors: the heart's lateral position to the left side of the body and the historical use of hand-held weapons, such as swords and spears. The heart's predominantly left position in the ribcage makes it vulnerable to fatal strikes. Similarly, wielding a weapon with the left hand causes a rotation of the left side of the chest, making it a more accessible target for an opponent compared to using the right hand.

These theories represent just a fragment of the evolving scientific landscape. However, one thing remains clear: the dominant influence, be it scientific, historical, or cultural, isn't set in stone yet. Scholars agree on the need for a deeper understanding to unravel the intricate biological mechanisms underpinning left-handedness. Meanwhile, it's heartening to see that excellence is within reach for both groups. And isn't it telling, among other proofs, that five of the last nine U.S. presidents were left-handed?