As part of their continuing work on establishing that there are archaeological remains in Brazil dating to the Last Glacial Maximum (LGM) or earlier, Boëda et al. (2021) present a techno-functional analysis of a piece recovered in an LGM layer in their excavation at Vale da Pedra Furada. As usual by now with claims of very early archaeological material in the Americas, the problem is not with the dating of the context. The dating, the stratigraphic, and geological work in general are impressive. The problem, rather, is with the claim that the find is archaeological. There are a couple of aspects of this report that go to the heart of what and how we know about the past.

While the authors introduce a few of the thousands of claimed artefacts recovered in the excavation, they focus on one particular piece, Artefact 255660, a “silty sandstone plate 21.0 cm long, 18.5 cm wide and 2.9 cm thick” (Figure 1) which they claim has “irrefutable anthropogenic character.” Their claim is that this single object is sufficient to establish a 24 000 year old archaeological signal at Vale da Pedra Furada.

If we accept that the piece could indeed be anthropogenic (i.e. a stone tool made and used by humans), or if we even grant that it is likely to be, there is still a fundamental problem with focusing on one object out of thousands recovered in a deposit, and claiming that it can establish the archaeological status of a site. Let’s explore why.

Figure 1: Artefact 255660 (Figure 10 from Boëda et al 2021)

In the absence of other evidence of human activity, stone tools can be very difficult to use on their own to establish the archaeological nature of a site. The forces that humans use to fracture stones into tools, and the forces they use to leave use wear traces on those tools, can also be exerted by a number of non-human agents. Objects that are produced by geological rather than human forces and look like stone tools, for example, are sometimes called eoliths.

In the early 1930s, AS Barnes (1939) solidly established that the way to distinguish between anthropogenic stone tools and geologically produced eoliths, was not to look at individual objects for tell-tale signs of human activity, but rather to look at statistical differences between assemblages, or groups of objects.

Figure 2: Artefact 255660 in context (Figure 4 from Boëda et al 2021)

Archaeologically, the basic question is this: How many rocks of a certain type would we have to put through how many years of geological and processes of certain kinds, to produce one that looks just like a tool made by a human? Given enough time, enough rocks, and enough geological processes, we can expect that this would happen. Unfortunately, we don’t know how many, or how long for each type of rock and each set of geological and environmental processes. This means that we can’t decide how confident we are that a particular object was not created by non-human forces.

Another factor is the morphology of the object itself. Producing a spectacular Acheulian handaxe would require the operation of very many forces, over a very long time, on very many rocks. At some point, we can express a moral certainty that an object must indeed have been produced by humans. Boëda et al.’s Artefact N˚ 255660 is not one of those. I am confident that there is a manageable number of forces, over a manageable time period, over a manageable number of rocks, that would produce this one rock without human intervention.

Then the question becomes: Is Artefact N˚ 255660 very surprising without human intervention? Or is it just a little bit surprising? Or not at all? We don’t know. We have no idea. It could be anthropogenic. But based on the information presented in the article, I don’t know that it is.

Just to complicate matters, humans are not the only biological force endowed with intentional agency that could have produced the object. Research on stone tool use by capuchin monkeys is ongoing in the region (Falótico et al. 2019), some of it in Serra de Capivara itself, the park where Vale da Pedra Furada is located.

Capuchin use rocks to break things and dig them up, among other applications. In the process, some of those rocks get fractured. Repeated use and fracture can look remarkably like human stone tool production. The oldest capuchin stone tool assemblages so far known in that region are about 3000 years, but there is no reason to think that the tradition can’t be older.

Given the multiplicity of processes that can produce something that looks like anthropogenic stone tool, the way forward here is not to focus on smaller and smaller elements of potential archaeological sites, eventually looking to a single object to show evidence of human presence. These kinds of problems, combined with concerns about the fragmentary nature of the archaeological record, lead Charles Perrault (2019), for example, to argue that we should privilege a macro approach to archaeological questions in almost every case.

The way forward for LGM archaeology in South America in general, is to look for multiple converging lines of evidence, such as anthropogenic environmental signals at the regional level, soil aDNA and organic remains at individual sites, or at least to statistically compare large lithic assemblage candidates to similar natural deposits nearby, to see if they differ in aggregate rather than in detail.

I wish Boëda and team every success, and I very much hope they find what they are looking for. There is no reason it shouldn’t be there. But so far, especially in this paper, they haven’t shown that it is.


Boëda E, Ramos M, Pe´rez A, Hatte´ C, Lahaye C, Pino M, et al. (2021) 24.0 kyr cal BP stone artefact from Vale da Pedra Furada, Piauı´, Brazil: Techno-functional analysis. PLoS ONE 16(3): e0247965. pone.0247965

Barnes AS 1939.The differences between natural and human flaking on prehistoric flint implements, American Anthropologist 41:99-112.

Falótico T  et al 2019. Three thousand years of wild capuchin stone tool use, Nature Ecology & Evolution 3:1034-1038.

Perreault C 2019. The Quality of the archaeological record, The University of Chicago Press.

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