The Mystery of Left-Handedness

Evolution has spent nearly 400 million years developing the intricate design of our hands, which are crucial to our daily lives. Yet, despite their remarkable design, about 99% of us end up favoring one hand over the other for everyday tasks like writing, high-fiving, and texting with one hand. It’s even more surprising that life itself seems to have chosen sides: our amino acids are predominantly “left-handed,” while our DNA forms a right-handed helix.

In the animal kingdom, where creatures often show a 50/50 split in paw, hoof, or wing preferences, humans are quite different. Only about 1 in 10 people are left-handed. So why are so few of us left-handed?

The world often seems to conspire against left-handers with a plethora of right-handed tools and gadgets—spiral notebooks, scissors, e-readers, video game controllers, zippers, and can openers. Even the language reflects bias: to be “correct” or “good” often means to be “right,” while “left” historically connotes “weak,” and words like “sinister” and “gauche” have negative undertones.

Interestingly, our brains are cross-wired, meaning the right hand is controlled by the left hemisphere and vice versa. However, the brain isn’t perfectly symmetrical. In the 1860s, French scientist Paul Broca discovered that the area of the brain responsible for speech processing is typically located on one side. Today, we know that 99% of right-handers have this area in the left hemisphere, while 70% of left-handers also have it on the left, with 19% processing speech in the right hemisphere and 20% using both.

This leads to confusion as the connection between language and handedness isn’t straightforward. Two theories help explain this. One suggests that a gene mutation, called the Right Shift mutation, may cause the brain’s functions to favor one hemisphere, leading to handedness. Individuals with two copies of this gene have their language and handedness centered in the left hemisphere. Those with one copy have a slightly reduced shift, and those without the mutation can have language and handedness in either hemisphere by chance.

Another theory traces handedness back to our embryonic development. Some genes that determine the orientation of our internal organs may also influence brain asymmetry. Despite these theories, the exact reason for the low prevalence of left-handedness remains uncertain.

Left-handedness persists, despite evolution favoring right-handed coordination, because left-handers provide a strategic advantage in competition. In sports like baseball or tennis, left-handed players often outperform their right-handed opponents simply because they are less common and therefore less practiced against. Additionally, having a variety of brain types, including those of left-handers, may offer cognitive benefits like enhanced creativity due to increased cross-talk between brain hemispheres.

While we don’t yet have all the answers, studying handedness continues to provide valuable insights into brain function and human diversity. The existence of left-handers highlights the fascinating variety within our species and reminds us that nature values diversity and variation.