International Lefthanders Day 2024: Unveiling the science behind left-handedness

Left-handedness, a trait seen in approximately 10.6% of the global population, has long intrigued scientists, psychologists, and the public. Understanding why some people are left-handed reveals fascinating insights into human biology. As Mobondeep Singh, a class VIII student at Apeejay School, Model Town, shares, “I feel proud to say that I am left-handed on this International Left-Handers Day! This day is a celebration of the uniqueness and creativity of left-handed individuals.”

Genetic factors in left-handedness

Genetics play a pivotal role in determining handedness. Research indicates that left-handedness often runs in families, suggesting a hereditary component. One of the most studied genes related to handedness is LRRTM1. This gene is believed to influence the brain’s asymmetry, affecting handedness. Specifically, LRRTM1 may impact how the brain’s hemispheres are organised, contributing to left-handedness.

Studies show that LRRTM1 interacts with other genes involved in brain development and lateralisation. For instance, variations in LRRTM1 can affect the development of the corpus callosum, the structure connecting the brain’s hemispheres. This interaction among multiple genes underpins the polygenic nature of handedness, making it a complex trait. Recent research also points to other genes, such as ROBO1 and PITX1, which may further influence handedness, though their exact roles and interactions are still under investigation.

Neurological differences in left-handed individuals

The brain’s structure and function are intricately linked to handedness. Most right-handed individuals have language and motor skills predominantly managed by the left hemisphere of the brain. In contrast, left-handed individuals often show a more balanced distribution of these functions across both hemispheres or sometimes a dominance in the right hemisphere.

Neuroimaging studies, including fMRI and PET scans, reveal that left-handed individuals exhibit distinct brain organisation compared to right-handed individuals. For example, research has shown that the planum temporale, a region associated with language processing, is often larger in the left hemisphere of right-handed people but can be equally developed or even larger in the right hemisphere of left-handed individuals. These differences in brain structure and connectivity contribute to the unique cognitive and perceptual abilities observed in left-handed people.

Developmental factors influencing handedness

Handedness begins to develop in the prenatal stages. Research suggests that fetal movements, influenced by brain activity, play a role in determining handedness. Studies using ultrasound and movement tracking have found that left-handed individuals may exhibit different patterns of prenatal movements compared to their right-handed counterparts. These movements are linked to the brain’s lateralisation process, where one hemisphere becomes dominant for certain functions.

Environmental factors also influence handedness. Maternal stress during pregnancy and early childhood experiences can interact with genetic predispositions, shaping handedness. For instance, some studies suggest that high levels of maternal stress might increase the likelihood of a child being left-handed. This interplay between genetics and environment highlights the complexity of handedness development.

Practical implications for left-handed individuals

Understanding left-handedness extends beyond academic interest; it has practical implications. Left-handed individuals often face challenges in a predominantly right-handed world. As Mobondeep Singh insightfully points out, “Despite the occasional challenges we face in a world designed for right-handers, we thrive and excel in all areas of life.” Common tools and writing instruments are designed for right-handed users, which can make daily tasks more cumbersome for left-handed people.

To address these challenges, research has led to the development of specialised products. Ergonomic left-handed scissors, left-handed desks, and custom-designed tools are among the innovations aimed at improving the daily lives of left-handed individuals. These products not only enhance comfort and functionality but also promote inclusivity in design.

The science behind left-handedness is a blend of genetics, neurology, and developmental factors. While significant progress has been made in understanding why some people are left-handed, the complete picture remains complex. The distinctive attributes of left-handed individuals, from brain structure to developmental patterns, underscore the diversity of human biology.

As research continues, Apeejay Newsroom gains a deeper appreciation of the complexities surrounding handedness and its broader implications for individuals and society. Future research could explore how genetic and environmental factors interact in more detail, potentially leading to new insights and innovations. By celebrating the uniqueness of left-handed individuals, as Mobondeep Singh emphasises, “Here’s to embracing our left-handedness and celebrating our greatness,” we continue to uncover one of the most intriguing aspects of human behaviour.