Ancient bones suggest “lefties” have been coping with a right-handed world for more than half a million years. A study of Homo heidelbergensis, an ancestor of Neanderthals, seems to show that the ancient humans were predominately right-handed.

“Finding that a hominin species as old as Homo heidelbergensis is already right-handed helps to trace back the chain of modernity concerning hand laterality,” says Marina Mosquera, a paleoanthropologist at Universitat Rovira i Virgili in Tarragona, Spain, who was involved in the study.

Humans are the only animal believed to show a strong preference for performing tasks with one hand or the other. Determining when right-handedness first evolved could shed light on traits linked to lateralised brains, such as language and technology, Mosquera says. Efforts to solve this mystery have looked to ancient human skulls and marks left on tools.

But these methods may not be reliable. Two-million-year-old tools carved out of animal bones contain marks that might be indicative of use by right-handers; however left-handers could have created the same patterns, she says.


Similarly ancient skulls may have been split into two hemispheres, but these changes could also reflect language processing, which occurs predominately in the left brain of both right-handed and left-handed people, Mosquera says.

‘Third hand’

In search of a less ambiguous indicator of handedness, Mosquera’s team looked to teeth, of all things. Ancient humans probably used their teeth like a third hand, she says, clenching onto meat and other objects to cut them with stone tools. And in the process, ancient humans might have grazed their incisors, creating diagonal marks.

To avoid cutting their noses off, ancient humans probably moved their blade in a downward motion, causing right-handers to make tooth marks in one direction, left-handers in another. Mosquera’s team confirmed this bias by asking left and right-handed assistants to simulate the process while wearing mouth guards.

Next, her team analyzed 592 cut marks on 163 teeth found at Sima de los Huesos cave in northern Spain, which has produced a trove of Homo heidelbergensis remains. The vast majority of the marks looked to be made by right-handers, Mosquera’s team found.

Indeed, out of the 19 individuals to whom the teeth belonged, 15 appeared to be right-handed and none left-handed. Teeth from four individuals contained mostly vertical marks and, therefore, could not be interpreted.

‘Same old problems’

Travis Pickering, a biological anthropologist at the University of Wisconsin in Madison, agrees that dental marks are a good way of determining handedness in ancient humans. “Most hominins, even early hominins, are going to be bright enough not to bring a blade up to their noses,” he says.

But the new study runs into the same problems as other attempts to understand ancient human behaviour by analysing marks left on teeth or tools, Pickering says.

A right-handed lab assistant may create diagonal marks across a tooth guard while using a stone tool, but cut marks on a 500,000 year-old tooth could have come from entirely different activities or even natural wear and tear.

Journal reference: Evolution and Human Behavior (DOI: 10.1016/j.evolhumbehav.2009.03.001)