We’re All Right: The Complex Science Of Left (And Right) Handedness

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Over the course of history, lefties have encountered some unfortunate prejudices.

Myths regarding left handedness are embedded fairly deeply in our culture. The word “sinister” likely comes from the Latin word for “left hand,” and the Bible has more than 20 negative references to left handedness, per BBC History Magazine. In some societies, southpaws are forced to learn to write with their right hands—a practice that may cause changes in brain structure and disrupt development, per recent research published in the Journal of Neuroscience.



Of course, much of the stigma surrounding lefties has disappeared over the past several decades, thanks in part to neurological breakthroughs. We now know how common left handedness is—about 10 percent of the world population is left handed—and that men are slightly more likely to be lefties than women.

With that said, scientists have had trouble figuring out why left handedness exists. Why isn’t everyone right handed? Why didn’t evolution weed out left handedness? (Sorry, southpaws.)


Now, thanks to recent research, we might have a decent idea of how handedness works. Strap in, because you’re about to learn more about your hand preferences than you ever thought you’d need.

To understand what causes handedness, it’s important to understand what “handedness” really means.

First of all, handedness isn’t hard and fast. Some people might use their left hands to write, but favor their right hands when playing sports. To researchers, that’s an important distinction, since handedness seems associated with brain asymmetry.

To put that another way, lefties use different parts of their brains for certain tasks than righties would use for the same tasks. That’s pretty obvious, right?



However, if you’ve heard the old chestnut that “the right side of your brain controls the left side of your body,” you should know that that’s an oversimplification.

“The ‘left-brain, right-brain’ thing sort of exaggerates these mythical ideas,” says Michael Corballis, PhD, emeritus professor at the department of psychology at the University of Auckland in New Zealand.

… Jimi Hendrix was undoubtedly a gifted guitarist, but we can’t ignore all the great right-handed guitarists that outnumber him.

“The dichotomies we like to think of were sort of superimposed onto the brain—[the idea that] one side is rational versus intuitive, one controls language and one controls emotion. Those things were sort of deposited in popular culture as though the brain were a dichotomy, but in fact, the two sides of the brain are much more alike than they are different.”

That leads us to our first bit of bad news for lefties: Left-handed people aren’t any more creative than righties, contrary to popular belief. How did we develop that myth?



“I partly attribute it to the divergent culture of the 1970s, which was when [scientists] showed that language is on the left side of the brain,” Corballis says. “It built up the idea that the right brain is somehow the organ of creativity. It was kind of a romantic idea, I think—maybe based on this idea that we had at the time that the East was somehow more creative and beautiful than the West.”

Unfortunately, that’s not how things work. There’s no evidence that handedness influences creativity, at least on a biological level.

“This is a myth, I’m afraid, mainly based on anecdotes (little scientific support and a lack of replication),” Erik Domellof, associate professor of psychology at Umeå University, tells Urbo via email. “For example, Jimi Hendrix was undoubtedly a gifted guitarist, but we can’t ignore all the great right-handed guitarists that outnumber him. Left-handers have been suggested to be more variable in cerebral organization, suggesting that some could be more creative, but also right-handers may have a variable cerebral organization and be equally creative.”



To simplify that: Being left-handed means that you prefer to use your left hand. It doesn’t necessarily mean anything else.

We do know that right handedness begins early—like, really early—in human development.

“It looks like [right handedness] is there from the start,” Corballis says. “It can be detected as early as the first trimester, I believe. Ultrasounds show movements of the right hand being more vigorous than that of the left.”

Sometimes, the signs of right handedness are even more obvious.

“The fetus can be detected sucking the thumb via ultrasound, and in something like 70 percent of cases, it’s the right thumb,” Corballis says. “So there’s evidence of handedness as early as that.”


iStock.com/Aslan Alphan

“There are basically no obvious gross differences in anatomy [between right- and left-handed people],” Domellof writes. ” … Although differences in the pattern of cerebral organization may occur, the idea that handedness is exclusively explained by differences in brain structure is too simplistic.”

In layman’s terms, left-handed people might have different brain structure than right-handed people, but that’s secondary—the brain develops differently as a result of handedness, not because of it. In fact, a recent study suggested that handedness starts in the spinal cord instead of the brain.



And in a systematic review and meta-analysis, Domellof’s team found that non-right handedness (meaning left handedness or ambidextrousness) seems to occur more often in pre-term births. We’ll let Domellof explain what that means. Bear with us, because this gets…wordy.

“Assuming that there is a neurological base for handedness, it is reasonable to believe that an early insult to the developing brain (which is a risk in the case of preterm birth) may cause a deviation in hemispherical organization,” Domellof writes. “… However, the mechanisms underlying altered handedness in children born preterm, and how this may associate with other functions and behaviors, are still unknown. More research [is] needed.”


We know that’s a bit dense, so we’ll try (and inevitably fail) to simplify it. Essentially, Domellof’s research could indicate that left handedness and ambidextrousness occurs due to external factors—not genetics, or at least, not exclusively. That’s just one theory. As we’ve seen, it’s a remarkably complicated issue—it’s not exactly brain surgery, but it’s pretty darn close (literally).

Corballis believes that, technically speaking, left handedness doesn’t exist.

Okay, that’s a bit dramatic. More accurately, he thinks that we should use different terminology when discussing it academically.

“I don’t think that left handedness itself is genetic,” he says. “I think what’s genetic is the degree of right handedness. Some people get born without the genetic push to be right handed. In those people, handedness is a matter of chance, as it is in a lot of animals. So, I think left handedness is really, genetically speaking, the absence of right handedness.”

That’s not exactly intuitive, but think of it this way: Genetics might give a person a preference for using their right hand, but in small number of cases, those genetics aren’t there, or deviations in development prevent them from taking hold. Those people might develop a preference for using their right or left hands—but that’s mostly up to chance.

“It almost looks as though they didn’t get the genes that makes [a person] right handed,” Corballis says. “… But whether these types of things are inborn, or genetic, or imposed by culture—I think the answer, usually, has to be ‘both,’ which can be a bit frustrating. Everything is half true.”

So, given what scientists have discovered about handedness, are there any advantages—or disadvantages—to being a lefty?

The simple answer is “no.” Contrary to popular belief, left-handed people don’t die earlier than righties, and Corballis says there’s not scientific evidence to suggest that lefties are naturally predisposed to specific personality traits. Recent research shows that handedness has no bearing on creativity or introvertedness.

However, ambidextrous people—people who don’t express a strong preference for either their right or left sides—don’t get off the hook so easily. Ambidextrousness is associated with deficits in academic development, certain mental health issues, and schizophrenia.



Why? To grossly simplify things, ambidextrous people don’t have the brain asymmetry that other people have—they’re closer to the mythical dichotomy. That’s not a good thing, since our brains are designed to be asymmetrical.

“A more random allocation of functions to either side of the brain seems to cause [problems],” Corballis says. “Not everyone agrees with this, but stuttering, for instance, might be caused by each side of the brain trying to take control of speech, so there’s a conflict. Things like reading disabilities seem to be more common in ambidextrous persons. But you’re never quite sure, of course, whether this is a cultural thing; whether people who are different are somehow subject to more pressure.”

And that doesn’t mean that ambidextrous people don’t have certain advantages.

“Some sportsmen who are ambidextrous do better than people who are left- or right-handed, for instance,” Corballis says. “… It may be that being somewhat ambidextrous and having a more balanced brain might have been advantageous, from an evolutionary perspective, perhaps for something like fighting.”



At the end of the day, hand preference isn’t particularly important, although it’s absolutely fascinating to neurologists and psychologists. As Corballis reminded us, five of the past eight U.S. presidents were lefties (Barack Obama, Bill Clinton, George H.W. Bush, Ronald Reagan, and Gerald Ford, in case you’re curious), so there’s nothing to stop left-handed people from succeeding in modern society.

So congratulations, lefties, you’re officially normal. Hopefully, that’s some consolation for never being able to use a pencil without getting graphite all over the side of your palm.

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