I mentioned yesterday the new Nature paper showing evidence of tool use promoting carnivory in Australopithecus afarensis. The evidence—ungulate bones with crush or cut marks that seem likely to have been made with stone tools—pushes back tool use in our ancestors/close relatives to 3.4 million years ago, 800,000 years earlier than we previously thought.
I’ve now gone through the paper and will clear up a few issues:
What kinds of marks were there? There were cuts, probably made by a sharpened stone used to cleave meat from the bone, and “percussion marks,” where the bone was crushed to extract the marrow.
How do we know that these are real toolmarks and not something else? Could the “cuts,” for example, be toothmarks from animal preadators and not hominins? We don’t for sure, of course, but I know that evolutionary anthropologists have spent a lot of time, including replicating the actions of hominins with stone tools, trying to distinguish between animal carnivory, natural abrasions, and real tool use. I don’t know a lot about this, but clearly these speculations were not off the cuff. The cuts certainly look real (see photo from yesterday)! But of course there is some dissent: Tim White, who has worked at the site for 40 years, observes that his team has never found a stone tool and that that the authors’ “claims greatly outstrip the evidence.”
Why didn’t they find stone tools at the site? This of course is the most serious caveat. The authors suggest that while tools were used at the site to extract meat and marrow, they were made somewhere else: a place where the right kinds of stones were numerous. According to the paper, the fossil site was not like that:
No stone artefacts or sharp-edged stones were found in association with the bones at DIK-55. However, stone tool production and consequently archaeological accumulations are not expected at this locality given the sedimentary environment characterized by the palaeo-Awash River emptying into a nearby lake. In this relatively low-energy depositional environment, clasts suitable for stone tool production are not present (few particles larger than fine gravel, 8 mm diameter).
This, in turn, would imply that the tools were being carried about by the hominins, perhaps in anticipation of finding a kill. Could they have been hunting instead of scavenging? If so, what were they using to kill the ungulates?
If these were toolmarks, what were the tools like? Some readers have speculated that, if the hominins simply used naturally sharp stones, we wouldn’t recognize the tools as “tools.” (This might well have been the case for blunt stones used to crush the bones for marrow.) The Nature paper, however, refers to sharpened stones, which means that humans sharpened them and didn’t just look for naturally sharp stones. (Indeed, naturally-occurring stones sharp enough to cut meat from a bone might have been nonexistent.) I’m not sure how evolutionary anthropologists define “tools,” but in this case I think they’re suggesting stones that were sharpened by hand. This is also implied in their search for”stone artefacts” and “clasts suitable for stone tool production.”
Here’s a cast from what is considered an unambiguous human tool: a chopper with flakes struck off. This might have been used to take meat from bones or, alternatively, the removed flakes could have been used as knifeblades. Or both. Worked stones like this “Oldowan” specimen, first seen about 2.5 million years ago, were the earliest known stone tools before yesterday’s announcement.