Earliest known evidence of right-handedness discovered

Statistics show that as many as nine out of 10 people are right-handed, and while it is difficult to say exactly when this particular preference first arose in humans, a new discovery by researchers from the University of Kansas reveals that it has been around for at least 1.8 million years.

Evidence to support the claim came in the form of an recently-found upper jawbone belonging to a human ancestor known as Homo habilis, which National Geographic explained lived in eastern and southern Africa between 1.4 and 2.4 million years ago, and which was believed to have been a regular user of stone tools (as suggested by their presence around the fossil discovery site).

Writing last week in the Journal of Human Evolution, KU anthropology professor David Frayer and his colleagues reported that the jawbone still contained its teeth, and that diagonal scratches (or, more formally, labial striations) on these teeth were likely made when the individual nicked them while using a stone tool held in his or her right hand.

“We think that tells us something further about lateralization of the brain,” Frayer, who was the lead author of the recently-published paper, said last Thursday in a statement. “We already know that Homo habilis had brain lateralization and was more like us than like apes,” he added. “This extends it to handedness, which is key,” because as he pointed out to Nat Geo, right-handedness, brain lateralization and language are linked – they “all fit together in a package.”

Findings could provide clues about other areas of human development

Frayer’s team identified the labial striations on the lip side of anterior teeth located in the upper jaw of a fossil known as OH-65, which was found near Tanzania’s Olduvai Gorge. The deep cut marks were found on the lip face of the upper front teeth, with most veering from the left down to the right, suggesting they were made with a tool held in the individual’s right hand.

More specifically, analysis of the scratches made using a microscope indicated that they were the result of the individual using a tool held in the right hand to cut food being held in the mouth and while he or she was pulling on it with the left hand. The subject (who was possibly female) made the marks by occasionally missing and striking the labial face, Frayer said.

Based on the direction of those marks, he added, it becomes apparent that the Homo habilis was right-handed, making this the oldest known evidence of a pre-Neanderthal with a dominant hand. Since the right hand is controlled by the brain’s left hemisphere, which is the same region of the brain that controls language, the discovery could provide some clues regarding the evolution of language in our ancestors.

“Handedness and language are controlled by different genetic systems, but there is a weak relationship between the two because both functions originate on the left side of the brain,” Frayer explained. “One specimen does not make an incontrovertible case, but as more research is done and more discoveries are made, we predict that right-handedness, cortical reorganization and language capacity will be shown to be important components in the origin of our genus.”

“We think we have the evidence for brain lateralization, handedness and possibly language, so maybe it all fits together in one picture,” he added. Scientists believe that it is likely that brain reorganization, tool use and dominant-handedness all occurred at an early point in our evolution, and the KU researchers may be close to finding the exact point where they occurred.

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Image credit: University of Kansas

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