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Tuesday, May 26, 2009

H. heidelbergensis teeth may show handedness

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.
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.

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