From the moment children first pick up a crayon, their dominant hand often becomes apparent. But why do some people favor one hand over the other, and why are left-handed individuals so uncommon?
The answer to this intriguing question is deeply rooted in science, history, and evolution.
The Science Behind Handedness
Handedness is not limited to hands; humans exhibit lateral dominance in various organs, such as eyes and ears. A simple experiment can reveal your dominant eye: extend your arm, raise your thumb, and focus on it with both eyes. Then, close one eye at a time. The dominant eye will retain a closer representation of depth perception. Similarly, many people have a preferred ear for phone calls or eavesdropping. Research indicates that while 40% of people are left-ear dominant, 30% have a dominant left eye, and 20% prefer their left foot. However, only 10% of the population is left-handed.
Evolutionary Perspectives
Historically, being left-handed carried societal stigma. Linguistic biases reflect this, with the word "left" deriving from Anglo-Saxon "lyft," meaning weak, while "right" in Latin translates to "dexter," implying skill and righteousness. Yet, evolutionary advantages underlie handedness. For instance, chimpanzees demonstrate task-specific hand preferences. In termite fishing, they use one hand consistently, refining their technique over time to increase efficiency.
However, while chimpanzees are evenly split between left- and right-hand preferences, humans overwhelmingly lean towards right-handedness. This disparity dates back to our ancestors. Evidence from Neanderthal teeth suggests their handedness distribution mirrored that of modern humans, with only 10% being left-handed. Scratches on their teeth indicate they held food with their non-dominant hand while using tools with their dominant hand, leaving clues about their preferences.
Genetic and Developmental Factors
Handedness is largely determined by genetics. Studies reveal at least 40 genes contribute to this trait, but the specific mechanisms remain unclear. Despite ongoing research, the question of why left-handedness is so rare remains unresolved.
Everyday Challenges and Myths
Left-handed individuals often face challenges due to tools designed for right-handed users, such as scissors and pens. There are also long-standing myths about left-handedness affecting brain function. The brain's right hemisphere controls the left hand, while the left hemisphere controls the right hand, leading some to believe left-handedness influences brain structure.
Chris McManus, a psychologist at University College London and author of Right Hand, Left Hand, suggests left-handedness might confer unique cognitive advantages. "Left-handed individuals often have different ways of thinking, which can result in extraordinary skills," he explains. However, Oxford University professor Dorothy Bishop counters that such claims may stem from selective reporting. While studies suggest left-handers are overrepresented in fields like music and architecture, these findings often lack robust evidence.
Bishop notes that rare conditions, such as Down syndrome and cerebral palsy, show a closer balance of left- and right-handed individuals, challenging the 1:10 ratio. This suggests that left-handedness may sometimes be a symptom rather than a cause of underlying issues.
Insights from the Insides
Fascinatingly, a baby’s handedness is determined before birth. Research by Peter Hepper at Queen’s University Belfast reveals that nine out of ten fetuses prefer sip their right thumb—a ratio consistent with the prevalence of right-handedness in the population. Follow-up studies confirmed these preferences persist into childhood.
Despite societal biases and myths, left-handedness remains an integral aspect of human diversity. While genetics and development shape this trait, much about the neurological and evolutionary origins of handedness remains a mystery. For now, the rarity of left-handedness continues to intrigue scientists and enrich the study of human behavior.
Why are some people left-handed? - Daniel M. Abrams
Video by TED-Ed
