Right-handed Habit May Have Started 2 Million Years Ago

A new study suggests that right-handedness may predate modern Homo sapiens. Prisma/UIG/Getty Images

Civilization has been constructed for the needs of the right-handed. Lefties complain about this, but nine out of 10 humans worldwide favor their right hands for tasks like writing, eating, turning doorknobs and chopping food. We are, as far as we know, the only animal that shows this kind of preferential handedness — even chimpanzees don't rely on one hand over the other. When, then, did humans begin this habit of handedness? A new study published last week in the Journal of Human Evolution, provides evidence that the human right-handed preference might have begun much, much longer ago than previously thought.

Until recently, scientists figured the right-hand preference started with the Neanderthals, or possibly with their more immediate European ancestors, which would make right-handed dominance among hominids about 430,000 years old. But this new research suggests that a far more distant human ancestor, Homo habilis, might have been the first right-hander.

Conceptual image showing four stages of human evolution; Australopithecus, Homo habilis, Homo erectus and Homo sapiens.
Science Picture Co./Getty Images

What tipped researchers off to this possibility was found not on the hands, but on the teeth, of a 1.8-million-year-old H. habilis fossil, found over a decade ago in a stream bed in Tanzania, surrounded by primitive chopping tools and the remains of large animals. The upper jawbone of this H. habilis fossil was intact, still bearing all 16 teeth. The fronts of some of these teeth, however, bore strange striations, most of them slanting downward from left to right and top to bottom.

The research team conducted experiments with modern human participants wearing mouth guards, acting out all sorts of likely scenarios with rudimentary tools, strips of meat and other tough materials to try and see what might have made these marks in the teeth. They realized these scratches might have been created by the mouth being used as a "third hand" while eating or processing food. For instance, one end of a strip of meat could have been held in the teeth to anchor it while the other end would be held taut with the left hand. The right hand, then, would hold a stone tool, which could be used to slice at the meat in the direction of the mouth. An inadvisable move, maybe, as the stone tool would occasionally hit the surfaces of the top teeth, but possibly very effective for scraping meat off a bone straight into the mouth. (Try that at your next backyard party. Or better yet — don't.) At any rate, it shows that this individual was probably right-handed.

"While this is just a sample of one, the specimen fits the pattern seen in Neandertals and their likely ancestors from Sima de los Huesos in Spain," says Dr. David Frayer, a paleoanthropologist and professor emeritus at the University of Kansas, in an email. "It also fits the pattern seen in modern humans that are right handed 90 percent of the time. Furthermore, we know that H. habilis used tools, and previous work has shown that they showed brain asymmetry. The left side of the brain controls the right side of the body, and this laterality is reflected in right-handedness. Right-handedness is also associated with language production in the left hemisphere. All this limited evidence fits together into a package."

Did he lose you at "brain asymmetry"? Let's unpack this paleoanthropological suitcase.

Handedness is of interest to scientists because it reflects the fact that humans have asymmetrical brains. The human brain itself is bifurcated, and though the two halves look exactly alike, they have different functions: the left side controls the right side of the body, and is specialized for language, while the right side of the organ controls the left side of the body, and is specialized for spatial recognition. The fact that humans have developed such sophisticated language has long been attributed to the fact that the left side of the human brain is more developed than the right, and preference for using our right hands supports this idea. This doesn't mean, incidentally, that left-handed individuals lack the language abilities of right-handers, but it might mean that our penchant for language started at least as far back as this one right-handed individual.

"We do not maintain that Homo habilis had language, but it does point to the consistency of this association in a fossil nearly two million years old," writes Frayer.