Plus vieux outils : la réaction de Dietrich Stout

This is obviously very exciting and greatly extends our knowledge of early human evolution and tool-making. The standard questions to ask about a report like this are: 1) is the date correct, and 2) are they really artifacts. I won’t really comment on question 1 since I’m not a geochronologist, other than to say it looks pretty convincing and even if the date moved a little they would still be the oldest tools in the world. Regarding question 2, what they illustrated looks pretty good. We always expected that earlier and earlier tools would be harder to differentiate from natural occurrences, but these seem convincing. The article says that 3d scans will be posted online after publication, so I’m very eager to look at those.

For decades, people have been conjecturing that there should be something “older than the Oldowan” because the earliest known Oldowan artifacts from the site of Gona look so skillfully made. Oldowan technology is conceptually very simple (knock a sharp flake off a river cobble) but this is harder to actually do than it might sound. Oldowan hominins did it is a skilled way that allowed them to get lots of useful flakes from each cobble. We’ve done experiments, and even for modern humans it takes quite a bit of practice to be able to do this. So, the expectation was that the first artifacts should really be more “crude” and inefficient in the way they were made. This is pretty much exactly what they have reported from Lomekwi – I couldn’t really design a find that would better fit these theoretical expectations.

So, why would we expect the earliest tools to be relatively crude in their manufacture? I think the underlying assumption favored by the authors is that they represent an earlier, transitional stage when hominins cognitive and motor capacities to understand and control stone fracture were less developed. I don’t disagree, but think the jury is still out on that. An additional possibility I would raise is that the tools are crude because the hominins didn’t make them very often or rely on them as much as was the case later in the Oldowan. This is basically an “economic” explanation. It takes a heavy front-end investment in practice to develop the kind of skill we see in the Oldowan, and this may not have been worth it if tool-making was a pretty rare thing. For example, think about learning how to touch type. If you are going to type a lot it may be worth it to learn, but otherwise you might do better not bothering and just sticking with hunt-and-peck. The Lomekwi site has a relatively small number of stone flakes and obviously we have not (yet) found a large number of sites at this early time. In comparison, the earliest Oldowan occurances from Gona reflect much more intense tool-making activity. (As the authors point out this is something else that was predicted by theorists- that the earliest artifacts should occur in “very low densities”). So it may turn out that technological differences have more to do with the cost-benefit trade-offs of practice rather than cognitive differences. Of course these explanations are not mutually exclusive, and could both be related to the “cultural” capacity for the Lomekwi hominins to learn skills from each other more or less easily.

Along these lines, I think it is very interesting that the authors interpret the tools as having been produced by bipolar and passive percussion techniques, rather than the free-hand technique that predominates in the Oldowan. These kinds of interpretations can be tricky, and I would like to see more of the experimental evidence that supports this interpretation, which I’m sure is forthcoming in future publications. But assuming this holds up, it is pretty cool. A recent experimental study by Shelby Putt (attached) found that if you don’t take the time to learn free-hand tool-making, methods such as bipolar and throwing can be more efficient. This would be consistent with an “economic expediency” interpretation of the technology at Lomekwi (and it would be really cool to see some experiments to test if the Lomekwi artifacts can be replicated with a throwing technique – something I think the authors have not yet looked into). In experiments teaching a bonobo to make stone tools, Nick Toth, Kathy and Sue Savage Rumbaugh found that the ape preferred throwing as a technique because it was easier. This is especially true because bonobo hands are less well suited to free-hand toolmaking. The real constraint is the ability to firmly hold the target core in the left hand while you bash it with a stone held in the right. All of these alternative techniques (passive hammer, bipolar, throwing) avoid the need for that, and thus may be easier both in terms of motor skill required and requirements for human-like hand anatomy. As the authors discuss in the supplementary materials, it is likely that hominins at this time were capable of “mostly human-like” manipulative functions but were less robust esp. in the thumb. This would also be consistent with relatively infrequent tool-making that did not require really firm grips on the core as in free-hand tool-making.