Mind & Body

Measure Your Right- or Left-Handedness With the Edinburgh Handedness Scale

Are you right- or left-handed? It turns out that regardless of your answer, your dominant hand could be more or less dominant than someone else's. You can find out just how right- or left-handed you are in a quiz linked below. The answer could have something to say about you.

Why Are Some People Left-Handed?

The short answer: Scientists aren't totally sure, but it's probably genetic. All sorts of animals show preference for one hand or another, from polar bears to chimpanzees. But in those populations, the split is nearly 50/50, with half of the population favoring one side and half favoring the other. Aside from a few animals, such as some birds and possibly chimpanzees, humans seem to be unique in sharing a preference for a certain hand: Around 90 percent of the population is right-handed. Some of this may be due to the fact that nearly 70 percent of the world still hates left-handers (so some people might be making an unnatural switch to avoid discrimination), but it probably has more to do with genetics.

In 2007, scientists identified a gene called LRRTM1 that most lefties seem to have. And in 2013, a group of researchers published a paper that proposes a whole network of genes that seems to relate to handedness. That suggests that handedness is more than a "dominant" or "recessive" trait as you might have learned in high school biology. Instead, it's likely related to many genes, making the genetic causes much more complicated.

This may also be why handedness isn't just a simple right-left dichotomy but instead is a spectrum. "Each gene has the potential for mutation," writes Natasha Geiling for Smithsonian.com. "The more mutations a person has in any one direction (toward right handedness or left handedness) the more likely they are to use that hand as their dominant hand, or so the researchers speculate."

More and more, scientists think handedness has to do with brain symmetry. 95 percent of right-handed people have brains that localize tasks to one side or another — for example, skills like language ability keep to the left hemisphere for most righties. But in left-handed folks, those tasks aren't as clearly divided. Only around 20 percent of lefties split tasks along hemispheric lines. There are some advantages to having a clearly divided brain since splitting tasks is more efficient and could allow for more clear thinking. But when both sides work on tasks together, that may lead to greater creativity (just ask Einstein).

A Sinister History

Lefties aren't just rare; they're also pretty special. There's a greater proportion of lefty athletes and U.S. presidents than in the general population, for one thing. Some studies show that lefties have more developed right brains, are better at spatial reasoning, and can even have strengths in math, architecture, and leadership. But for most of the world, that's not enough. Lefties are often retrained to use their right hand as the dominant hand.

An anti-left bias is even ingrained in our vocabulary. The Old English word for left, "lyft," means broken. And the German word, "linkisch," means awkward. The Russian word "levja" is associated with being untrustworthy. The Latin word for left is sinistra, which eventually also came to mean "evil" or "unlucky." Left-handers were associated with evil, threatening, sinister things by the early 15th century.

Language also evolved to associate "right" with justice, law, and correctness. In many European languages, as well as in English, "right" and "correct" are synonyms.

How Handy Are You?

You're probably pretty familiar with which of your hands is dominant, but that dominance is probably not as simple as you think. There's a questionnaire scientists use called the Edinburgh Handedness Scale to measure people's laterality, or how right- or left-handed they are, and it turns out that many people fall somewhere in the middle of the spectrum. You could use your right hand with scissors and your left hand for throwing. And that could have to do with genetics or with how scissors are made.

It could take a while before we know exactly where our handedness comes from, and what that means. But geneticist William Brandler, Ph.D., says that time is coming: "There's been a whole revolution in genetics such that, in a few years time, we're really going to start to understand the genetic basis of complex traits." You can get ahead of the curve by understanding your own laterality right now. And then you can decide if you're as "correct" or "sinister" as your handedness says you are.

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Want to read a cultural history of left-handedness? Then you'd better pick up "The Left Stuff: How the Left-Handed Have Survived and Thrived in a Right-Handed World" by Melissa Roth. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Kelsey Donk September 27, 2019

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