Most of us give little thought to which hand we use to pick up a cup, open a door or cut our food. We just reach. Yet roughly nine in ten people favor their right hand, a pattern that has long interested scientists studying how humans evolved.
How far back does that preference go? One answer may be written in a surprising place: the front teeth of an early human relative who lived about 1.8 million years ago.
The fossil, an upper jaw known as OH-65, was found at Olduvai Gorge in Tanzania and is attributed to Homo habilis. Researchers examining its teeth noticed fine scratches across their front surfaces. The direction of those marks suggests that this individual may have used the right hand to wield a cutting tool.
Why look at teeth?
If you want to know which hand an ancient person used, hand bones might seem like the obvious place to start. Fossils rarely make things that easy. Teeth often survive well, and they can preserve small marks left by actions performed during life.
Imagine gripping a piece of tough material between your front teeth. You hold it steady with one hand and cut it with a stone tool in the other. Now and then, the tool slips or brushes against a tooth. It leaves a scratch. Repeat that action over time, and the teeth may keep a record of how the cutting was done.
That is the explanation researchers proposed for the marks on OH-65. Many of the scratches slope in a direction consistent with a tool held in the right hand while the left hand helped hold or pull the material. Experimental work helped researchers test whether this kind of activity could produce similar marks.
It’s a small clue, but an intriguing one. The jaw survived for an extraordinary length of time, and so did the traces of an everyday task.
What the fossil can tell us
The study offers evidence of right-handed behavior in an individual from the early human fossil record. That makes OH-65 important: it pushes a recognizable sign of hand preference far back into our genus’s history.
There is a limit to the finding, though. One jaw cannot tell us how common right-handedness was across the whole Homo habilis population. The scratches support an interpretation of what this individual was doing; they are not a survey of everyone living at the time.
The marks also do not reveal what the person was cutting with certainty. Food is one possibility, but the central finding is about the likely movement of the hands and tool, not an identified meal.
Hands, tools and the brain
Hand preference interests researchers partly because the two sides of the brain are not identical in what they do. In modern humans, the left hemisphere plays an important role in language and typically controls movements on the right side of the body. That has led scientists to ask whether ancient hand preference might offer a clue about the development of brain specialization.
The connection is worth investigating, but it should not be overstated. Scratches on teeth cannot show exactly how an ancient brain was organized. They cannot tell us whether this individual had language like ours, either. What they can provide is a physical trace of a behavior—possibly using one hand more consistently for a skilled task.
An ordinary action, preserved for ages
It is easy to picture early human evolution only in big milestones: new species, changing bodies and the first stone tools. OH-65 brings the story down to a single motion. Someone held material at their mouth, worked at it with a tool and occasionally struck their teeth.
Those accidental scratches survived long enough for scientists to examine them. They don’t answer every question about why most people today are right-handed. They do give us a rare glimpse of how one ancient individual may have used their hands—and remind us that the smallest fossil details can preserve evidence of everyday life.
