Science Sunday: Old Bones, New Theories

The eminent entomologist Edward O. Wilson writes in his seminal The Diversity of Life that the first rule of the history of science is that when a big, new idea is proposed, an army of critics soon gather and try to tear it down.

Such is the case in one of the more fascinating debates now raging in the halls of anthropology: When did our human ancestors begin to use tools?

The focus of the debate are the animal bones with slash marks shown in the images above. They were recovered from Dikitka, Ethiopia and studied by a team led by Paleolithic archaeologist Shannon McPherron, who believes that the marks are the handiwork of stone tools wielded by prehistoric hunters at least 3.39 million years ago, some 800,000 years before the earliest estimates of tool use.

That predates the emergence of modern humans, which means that the tool-users probably belong to one of our ancestral species such as the famous Lucy.

McPherron's findings, published earlier this year, prompted the inevitable rebuttal, in this case by another team led by another Paleolithic archaeologist, Manuel Dominguez-Rodrigo.

This team argues that similar cuts can be produced when bones are gnawed by animals, trampled into rough ground, or even eroded by plants and fungi, and they conclude that trampling was the cause of the Dikika bones.

But McPherron stands by his work.

He says that he ruled out alternative explanations such as trampling in his original paper on the bones and that Dominguez-Rodrigo hasn't examined the original specimens and his criticism is based solely on the photos in a paper that McPherron wrote for Nature.

McPherron also points out that two of the most compelling marks -- known as A1 and A2 -- are clearly not caused by trampling, and Dominguez-Rodrigo agrees. He writes that the marks are "compelling in their similarity to verified cut marks created by stone tools."