Why are most people right-handed? Scientists analysed 1.8 million years old Teeth

One of the traits that make humans different than other species is our preference for using right hand. It has been estimated that 90% of humans are right-handed, according to scientificamerican.com. Scientists believe that this preference of handedness has played a vital role in the evolution of humans. A recent study in sciencedirect.com that studied fossil records for the evidence of right-handedness shows why the trait came into existence. Surprisingly, the evidences were based on our ancient teeth, and not in our hands.

The human brain is symmetrical, with two similar halves. It’s a known fact that left hemisphere is where the language and motor abilities take place, and the right hand is where visual-spatial distinction/analysis takes place. But some of the cognitive processes are dominant on one side of the brain, a uniquely human feature associated with improved cognitive ability, and it is known as brain lateralization.

Is it that the preference of hand or handedness has shaped the brain lateralisation? The clues lie in the ancient tools used by our ancients in the ancient civilizations.

Study finds striations on teeth of a Homo habilis fossil 1.8 million years old moved from left to right, indicating the earliest evidence in the fossil record for right-handedness. David Frayer


The oldest known tools used by humans dates 3.3 million years back and was retrieved in Kenya, Africa. They required a high level of dexterity, and the experiments conducted on replicating the tool-making process showed that the left side of the brain was more active.

Comparing to other species, humans are right-handed for making tools. The reason may be opposite function of two hemispheres in other species.

As it seems, there exists a relationship that handedness and brain lateralization could go hand in hand, though the relationship might not be straightforward.

But why are teeth used to understand the handedness? Because there are no left and right arm bones that have been found of our ancestors so that we can analyze it. If we can’t match the left and right-hand sets, then we can’t analyze the differences in size and shape to understand which hand was used for manual tasks.

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Teeth, however, last long and can establish handedness too.

How? Researchers found some striation, or scratches, on the front side of teeth of European Neanderthals. They assumed that the scratches were made when the ancient humans held one material while grabbing between the front teeth, and the other hand with a stone tool, such that these tools hit these teeth at times.

That experiment was replicated, but to be safe, the participants wore mouthguards. When the material is pulled with the left hand and stuck with the right hand, there were right-slanted scratches on teeth, proving that they were good signs of right-handedness.

The upper jawbone retrieved from ancient days gives the oldest evidence of right-handed in our genus Homo. It belonged to Homo Habilis, which means ‘handy man’ of Tanzania in Africa, sometime around 1.8 million years ago.

Teeth Marks

They found a number of slanted striations on the front side of teeth, and with scientific equipment, scientists found a particular pattern in their direction: they were mostly right-slanting. It was more slanting on the four of front teeth, giving the authors of the research enough reasons to believe that the person was using right hand most.

While the jaw shows the right-handedness in human, it also shows that there was already a high level of brain development in humans by at least 1.8 million years ago. This organization of brain has helped humans develop skills for tool making, and also for the development of language.

This article was originally published on The Conversation. Read the original article.

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