I Don’t Get It. Why Are Most People Right-Handed?

Science has something to say, but also some that can’t yet explain

Growing up, just like most families I know, each of us in my household of four had a place to sit at a table. However, unlike most of my friends, we had to replicate this configuration everywhere we were. That’s if we didn’t want some messes.

You see, half the people in my household are left-handed, including my sister. Sitting the wrong way would mean food spilling everywhere and knocking our arms when we ate. Doing crafts side by side? You’d rather sit us the right way.

However, my family situation was quite unusual. Humans are a pretty skewed species when it comes to handedness. Around 70–95% of people today prefer to use their right hand for most tasks. Nobody in my current family (now that I’m a father) is left-handed, which mimics the reality in human societies a bit more.

Even more, this pattern of most right-handed people has persisted for thousands of years, and there’s strong evidence that it has deep evolutionary roots.

But why is right-handedness so dominant, and what does science say about it? To answer that, we can look at a combination of fossils (yay fossils!) and what we know about the brain.

Scratches on Teeth and Bones

Surprisingly, one of the key ways we’ve learned about handedness in ancient humans comes from the scratches on their teeth. Imagine you’re a Neanderthal living 130,000 years ago, using your teeth to help stretch an animal hide while scraping it with a stone tool.

Every now and then, the scraper slips and accidentally leaves a mark on your front teeth. Well, by looking at the direction of these scratches, scientists have been able to determine which hand you were using.

For example, if the scratches run from the upper left to the lower right, it likely means you were holding the scraper in your right hand. This kind of evidence has been found in multiple fossils, including those of Neanderthals and even earlier species like Homo habilis, who lived nearly 1.8 million years ago.

Scratches on teeth aren’t the only clue, though. Studies of upper arm bones from ancient humans also show that the bones on the right side of the body were often thicker than those on the left, suggesting that the right arm was used more frequently, likely for tasks requiring strength and skill, like hunting or making tools.

Handedness and the Brain

But why are most humans right-handed, and what does that have to do with our brains? It all comes down to something called lateralization. Our brains are divided into two hemispheres, with each hemisphere controlling the opposite side of the body.

The left hemisphere, for example, controls the right hand. This separation allows us to process different types of information simultaneously, which helps with everything from walking to problem-solving.

In humans, brain asymmetry is more pronounced than in our primate relatives, and that might explain our preference for one hand over the other.

Most people (but not all people) have a dominant left hemisphere, which not only controls the right hand but is also heavily involved in tasks like language and fine motor skills. This left-hemisphere dominance is likely why the right hand became the “go-to” hand for most people throughout human history.

Tools and Walking Upright

Scientists think that our preference for right-handedness may have evolved alongside other uniquely human traits, such as tool use and walking on two legs. Tool use requires precision and control, and brain scans show that a region in the left hemisphere, called BA44, plays a big role in manipulating objects.

Since this region controls the right hand, it’s possible that early toolmakers were mostly right-handed, and over time, this preference became widespread in the species.

Bipedalism, or walking on two legs, might also be linked to handedness. Some bipedal animals, like kangaroos, show a preference for one hand (or paw), although they tend to favor the left side. In humans, the combination of bipedalism and tool use may have tipped the scales toward a strong right-hand preference.

Why Do Left-Handed People Still Exist?

Here’s where it gets complicated. Even though the majority of people are right-handed, about 10% of the population is left-handed. Why, though?

Left-handedness likely results from a combination of genetic factors and brain differences. Interestingly, left-handed people often have less lateralized brains, meaning they use both hemispheres more equally. This can come with some surprising advantages, such as better coordination, memory, and even an edge in competitive sports like boxing, where lefties can catch their right-handed opponents off guard.

Think of it as a superpower!

Researchers have also found that left-handed men may have an advantage in physical combat. Studies of athletes, particularly in boxing and martial arts, show that left-handed fighters tend to win more often than their right-handed counterparts, perhaps because they strike from unexpected angles. The surprise factor can quickly add up!

What Science Still Doesn’t Know

That said, despite decades of research, scientists still don’t have a complete answer as to why humans are mostly right-handed. Some studies suggest that there might be several genes involved in handedness, but a single “handedness gene” has yet to be found.

What’s going on, then? It seems more likely that a mix of genetic, environmental, and evolutionary factors has contributed to the patterns of handedness we see today. Culture has likely influenced too.

In the end, handedness is just another fascinating part of what makes humans unique. Whether you’re a righty or a lefty, the story of how this trait developed offers an intriguing glimpse into our evolutionary past.

And if you had a family like mine growing up, you provably have some funny (and messy to share).

Want a more visual cover of this story? Make sure to check out this PBS Eons episode on the topic!