Why Are Most People Right-Handed? (A Story from Prehistoric Times to Modern Day)

Imagine a Neanderthal cleaning an animal skin 130,000 years ago in what is now Croatia. Holding the skin between their teeth and pulling it tight, they scraped it with a stone tool.

Occasionally, the tool slipped and scratched their front teeth. These scratches reveal fascinating insights about the hands that made them.

Anthropologists, by examining the orientation of these scratches, discovered that most Neanderthals were right-handed, much like the majority of modern Homo sapiens—70 to 95 percent, to be precise. This right-handedness is unique to humans; no other placental mammal, not even our closest primate relatives, shows such a consistent preference for one side of the body.

Additionally, no human population has ever been predominantly left-handed. Our preference for one hand over the other is intertwined with other unique traits inherited from our ancestors after our lineage split with chimpanzees, such as walking upright and making stone tools.

Right-handedness may have deep evolutionary roots. However, being left-handed does come with some unexpected advantages.

Understanding Handedness

Handedness is not merely a preference for one hand over the other; it’s more of a spectrum. Some people are strongly right or left-handed, while others fall somewhere in between.

Even those who prefer their right hand for tasks requiring fine motor skills still use their left hand frequently in daily life. For example, when cutting up a carrot, one might hold the knife in the right hand and stabilize the carrot with the left.

In all vertebrates, each hand is controlled by a different side of the brain. The left hemisphere controls the right side of our bodies and vice versa.

The two hemispheres of our brain aren’t perfectly symmetrical, leading to different cognitive processes taking place in different parts of the brain. This separation, known as lateralization, allows us to process different types of information simultaneously.

Humans exhibit extreme asymmetry and lateralization compared to other primates, which may explain why we prefer one hand over the other.

Evidence from History and Evolution

Ninety-nine percent of people have a dominant hand, and this has been the case for a long time. Cave paintings from the Late Pleistocene, depicting wild animals and hunting events, also include numerous human hands.

These hands were likely made by placing one hand on the rock and spraying pigment over it, leaving an outline. The vast majority of these outlines are left hands, suggesting that the artists were predominantly right-handed.

Hand preference is so strong that it can be seen in the skeleton, especially among athletes like tennis players who use one arm more frequently. The bone of their dominant upper arm becomes thicker in certain places due to the increased force exerted on it.

Evidence suggests that our extinct hominin relatives were also mostly right-handed. Neanderthals, for example, had thicker upper arm bones on their right arms.

Interestingly, microscopic scratches on Neanderthal teeth caused by tools indicate handedness. Scratches on 500,000-year-old teeth from Homo heidelbergensis in Spain and 1.8 million-year-old teeth from Homo habilis in Tanzania show evidence of right-handedness.

This suggests that handedness emerged after our split from chimpanzees.

The Evolutionary Significance of Handedness

Why did more than one hominin species start preferring one hand, and why the right hand? Genetic studies have shown that handedness appears to be somewhat heritable, with men being left-handed more often than women.

However, no single “handedness” gene has been found. Instead, several genes might have minor effects, with other factors also at play.

Brain lateralization and tool use are crucial. A specific region of our left hemisphere, BA44, plays a vital role in manipulating objects, including making and using tools.

Since the left hemisphere controls the right hand, the development of tools might have led to this hand being favored across hominin species. Bipedalism might also play a role, as some bipedal mammals like kangaroos show hand preference, although they are mostly left-handed and don’t use tools like humans.

The Advantages of Being Left-Handed

Why do left-handed individuals still exist today? Lefties process information more evenly across their brains, potentially leading to better coordination, memory, and verbal skills.

This less lateralized brain structure might give them an edge in physical combat, as seen in sports like boxing and mixed martial arts. Left-handed athletes often win more matches due to the element of surprise against right-handed opponents.

This evolutionary advantage might explain why left-handed individuals are a consistent minority in a predominantly right-handed world. Like tool use, bipedalism, and other unique traits, handedness has a deep evolutionary history in our lineage.

Handedness illustrates the variability of our species and emphasizes that there’s no single “right” way to be human. Whether right or left-handed, our preferences and abilities have shaped our evolution in remarkable ways.