(New Scientist) Humans evolved beyond their vegetarian roots and became meat-eaters at the dawn of the genus Homo, around 2.5 million years ago, according to a study of our ancestors’ teeth.

In 1999, researchers found cut marks on animal bones dated at around 2.5 million years old. But no one could be sure that they were made by meat-eating hominids, because none appeared to have suitable teeth.

Now an analysis by Peter Ungar of the University of Arkansas has revealed that the first members of Homo had much sharper teeth than their most likely immediate ancestor, Australopithecus afarensis, the species that produced the famous fossil Lucy.

What sharp teeth you have...

Eating meat requires teeth adapted more to cutting than to grinding. The ability to cut is determined by the slope of the cusps, or crests. “Steeper crests mean the ability to consume tougher foods,” Ungar says. He has found that the crests of teeth from early Homo skeletons are steeper than those of gorillas, which consume foods as tough as leaves and stems, but not meat.

Ripe fruit

But the crests of teeth from A. afarensis are not only shallower than those of early Homo, they are also shallower than those of chimpanzees, which consume mostly soft foods such as ripe fruit, and almost no meat.

“Ungar shows that early Homo had teeth adapted to tougher food than A. afarensis or [chimpanzees]. The obvious candidate is meat,” says anthropologist Richard Wrangham of Harvard University.

Ungar used a laser to scan each tooth and mapped the surface as though it were a landscape, using a geographic information system, he told a symposium on diet and evolution at the University of Arkansas in August.

He had to find a way to compare teeth already worn by use, because unworn teeth are extremely rare in fossils. In a previous study on the teeth of gorillas and chimps, he validated the technique by showing that the differences between species’ teeth remain constant however much they are worn down (Proceedings of the National Academy of Sciences, vol 100, p 3874).