The Fascinating Reasons Most People Are Right-Handed
The science points in several important directions.
Around 130,000 years ago, there was a Neanderthal seated in a field while holding an animal hide with his front teeth. He stretched it with one hand, shaped it with the other, moving a rock across the top of the hide in cascading rows as it got closer to his teeth.
Every now and again, he slipped and the rock scratched the front of his teeth. The scratches these left on these teeth and those of his peers, all went in a specific direction, helping convince anthropologists that most Neanderthals were right-handed—just like us.
Though figures vary, estimates state around 70 to 95% of humans are right-handed (with most skewing on the higher end of those figures). And what’s interesting is that we know of no other mammal that skews so heavily to one side or the other. In apes for example, the preferences are roughly evenly split between left and right.
Even further, no culture of humans has ever been recorded as being left hand dominant. Conversely, we have ancestors, such as the Homo heidelbergensis, that were exclusively right-handed.
Here’s what we know about handedness, and why it skews in one way or the other.
Handedness Explained: Spectrum, Brain Asymmetry, and Evolutionary Insights
One misconception is that handedness is a singular state, when in reality it is a spectrum. There are many shades of right and left handed, who prefer doing certain tasks with their non-dominant hands.
Each hand is controlled by the opposite side of the brain. The two hemispheres aren’t perfectly symmetrical (this is especially true in humans and other large-brained animals). This asymmetry is theorized to play a role in why 99% of humans have one hand that is more dominant. It may also explain why this trait has transcended time.
Even in cave paintings, a majority of the painted hands, are left hands. Meaning the artist was placing their left hand on the wall, and tracing it with their right hand.
You can see it in the famous 10,000 year old painting, “The Cave of Hands”, found in the province of Santa Cruz, Argentina. Around three quarters of the hands are believed to be those of women:
Wikimedia Commons (Public Domain)
What’s amazing is that the same type of paintings were also created in France around the same time, without any transcontinental navigation.
Hand preference is so powerful in our species that it’s reflected in our bone structure. With tennis players, you often see thicker right hand and forearm bones (also called, Wolff’s law). One of my favorite images of this is of an x-ray of a pro tennis player’s forearms. Can you guess which hand they were swinging the racket with?
Unsurprisingly, this trend is also strongly reflected in the remains of our ancestors, lending further credence to the sticking power of right hand dominance.
Language, Brain Development, and the Evolution of Right-Handedness
One thing that especially separates us from other species is our incredible potential for language and communication. That is typically handled by the left side of our brain, which also controls our right hand. As we grow and our brain develops, rapidly learning language and communication, scientists think this rapid change may induce more right-handedness.
Scientists have scanned the brain and learned that a specific region on the left side of the brain, BA44, plays an important role in fine motor skills, which includes making and using tools. Hence, it’s possible that the prioritization in that skill played a big role in our species evolving towards right-handedness.
Why people are left-handed
We know there is a strong genetic element to handedness though it’s not a single gene or genetics alone. For example, two left-handed parents are more likely to produce a left-handed child.
Gender plays a role—with men slightly more likely than women to be left-handed.
It’s believed that prenatal development and environment can shape this prioritization as well. Twins are more likely to be left-handed. An analysis of 19 different studies of left-handedness in twins found that 15.09% of identical twins and 12.08% of fraternal twins were left-handed—compared to the overall frequency of left-handedness of 9%. This divergence may be tied to the polarity of fetal development with twins.
Additionally, there’s a theory of competitive advantages being given through left-handedness—as we see in sports and combat. Because the trait is uncommon, it renders opponents less able to deal with it.
What’s interesting is that your handedness is not directly correlated to your stance. A left-handed person is very likely to swing a baseball bat or stand on a skateboard in the same stance that a right-handed person does.
There is also the vanishing twin syndrome—which is when fetuses start out as twins and then, for one reason or another, one of them vanishes and is reabsorbed into the body. These cases may produce left-handed people more often. Scientists think it could be because of hormonal imbalances, and potentially elevated levels of stress with the loss of the other twin (with the elevated cortisol coming from the mother).
Lastly, there is a strong cultural element that maintains the world as a place for right-handers. Many families will force a child to switch and write with their right hand even if they are left-handed, because of stigma, or a desire for an easier life for that child. Educators even used restraints on children in the 20th century to keep them from using their left hand.
In fact, there’s a good chance one of you reading this was once left-handed, but no longer are.
The final takeaway
I wish there was a single gene or explanation I could leave you with today, some simple insight, “Virgos are responsible for all the left-handed people.” But as with many things in science—the answer is—it’s complicated.
We don’t fully know for certain why we prefer one hand or the other. But we still have a useful constellation of theories, supported by research, that at least partially explain why we skew one way or the other.
This is really interesting. My father is the only person I know of in my family that was left-handed. His father was fully ambidextrous. I would have thought that one of my generation would be left handed but my sisters and brother and I are all right-handed. And all of our children are right-handed. My father was always very careful where he sat at the table so that his left hand didn't negatively impact anyone else at the table during a meal.
Hi Sean, I am a left hander pushed in childhood to be a right hander. The end result is a mixture of ambidexterity and brain confusion🤣... The world is made for right handers, so are most appliances and gadgets and although I can usually get to grips with their usage, it is harder than it should be. My second daughter is left handed, but does complain about the difficulties in writing without smudging the text, at least I was compelled to write and eat as a right hander😊