Animal bones were recently discovered that suggested humans were using tools 3.4 million years ago - 800,000 years earlier than previously thought. But that finding is being challenged, and the story of human evolution hangs in the balance.
Shannon McPherron and his team at the Max Planck Institute reported back in August that they had discovered a pair of animal bones in Ethiopia that suggested ancient hominids had used them as tools. This was because the bones possessed damage that the researchers argued had been caused by stone tools. They theorized hominids had used stones to break through the outer bone and get at the marrow inside, which would be a simple but definite example of tool use.
Now Manuel Dominguez-Rodrigo and his colleagues at the University of Madrid are challenging these results, arguing the bones could just as easily be the result of natural scratches:
"A mark made with a stone tool could be morphologically similar to a mark that is accidentally made by an animal trampling on a bone, if the bone is lying on an abrasive [surface]. We can match mark-by-mark every single mark on the fossils with marks that we obtain using trampling criteria."
Dominguez-Rodrigo further explains just why this issue matters:
"This might seem like an obscure debate but if [McPherron and colleagues] are correct, the implications are huge. In the future, we may find traces of hominins eating meat and using stone tools long before we already know. But if they are right that means these features appear long before creatures had the brain to actually do this, from the interpretation we have from the last 40 years. So it's a big statement that has to have a special kind of evidence."
It's difficult to comprehend the real difference between 2.6 and 3.4 million years ago. Separated by 800,000 years, these time periods also saw different dominant hominin species. The earlier date was the time of Australopithecus afarensis, the most famous example of which is the Lucy skeleton. These creatures were bipedal, but still short, hairy, and small-brained - a modern observer would probably consider them more ape-like than human.
By the time of the earliest undisputed tool use 2.6 million years ago, Australopithecus afarensis had been extinct for roughly 300,000 years. We're not sure just which human ancestor was the first to use tools - it might have been Australopithecus garhi, or possibly Homo habilis. Both were considerably more human-like than afarensis, with brains large enough for tasks like tool use. As Dominguez-Rodrigo explains, if hominids really were using tools 800,000 years earlier than we thought, then we'll have to significantly reconsider our understanding of human evolution.
For his part, McPherron points out that Dominguez-Rodrigo have never actually seen the bones up close, instead working purely from photos:
"There are quite a few marks on these bones and on a few of them they think that the pattern that you see falls within the range you see for trampling. But the point is to explain the totality of the marks on these bones, and the totality fits very well within the pattern for cut-marked, or stone-tool-modified, bones."
This isn't the sort of debate that is easily settled. In all likelihood, it will continue until either more tools of similar age are discovered, or enough time passes without any new discoveries that the bones can be dismissed as outliers and probably a natural phenomenon.
[via BBC News]