The Cerutti Mastodon is back in the pages of Nature, this time with a critique by Ferraro et al (2018) of the original report (Holen et al 2017), and a reply by Holen et al (2018).  As others have done (e.g. Braje et al 2017, Haynes 2017), Ferraro et al (2018) point out that the evidence presented to support the archaeological nature of the Cerutti Mastodon site has a number of other, simpler explanations that do not involve the rewriting of human history. Last year, I evaluated some of the claims and gave a bit of background.

The idea that one single outcome (e.g. something that looks like a stone tool) could have been generated by many different processes (e.g. humans making a tool, or a geological process) is called equifinality. The related problem of multifinality is that a single process can produce diverse outcomes. Equifinality is an extremely important concept in archaeology. Since we can’t actually observe the past processes that generated the evidence we see in the present, we have to infer them solely from their observable outcomes.

The strictest form of respect for equifinality in archaeology requires that if we can imagine at least two ways in which things could have happened in the past to produce one set of observations in the present, we have to rule one out or remain agnostic. In practice, most of us accept, i.e. have a preference for, a simple enough, well supported enough explanation, when alternative explanations are less simple and less well supported. We should remain agnostic when explanations that are equally simple and likely can co-exist.

Yes, the bones at the Cerutti Mastodon site could have been broken by people, and the marks on the hammerstones and anvils could be the result of ancient human activity. However, they could also be the result of geological processes old and recent, and in some cases, the result of very recent human activity (road building work with heavy machinery). These alternative explanations are much simpler than the claim that humans produced the site over 100k years ago.

In order to accept a claim that humans produced the Cerutti Mastodon site 130 000 years ago, it is important to either rule out these simpler alternative explanations (to deal with equifinality), or to produce evidence of other, unequivocal human activity at the site, such as structured hearths, or formal, curated tool assemblages (none of which are present).

In their recent critique, Ferraro et al (2018) show that, far from being unequivocal evidence of human activity, the material at the Cerutti Mastodon site, specifically the bone breakage pattern, is similar to material found in comparable sites at which there is no suggestion of an ancient human presence. Normal archaeological reasoning would then suggest that the Cerutti Mastodon claim either must be left open, pending much more rigorous comparison of the material at the site, with material at these comparable non-archaeological sites (which I very much hope Holen et al will do), or that we must prefer the simpler alternatives.

Perhaps, as Holen et al (2018) contend in their response, the Cerutti Mastodon material really does differ in fundamental ways from the material Ferraro et al (2018) report from the Inglewood Mammoth site and the Waco Mammoth National Monument site. Perhaps the production of the Cerutti Mastodon material really does require ancient human activity, as opposed to the material at these two other sites, which is agreed to be the product of geological processes and recent heavy machinery activity. But we can’t take their word for it. They have to show it, just as Ferraro et al have shown that their material is at least potentially equivalent to that found at the Cerutti Mastodon site.

Until a better comparison is made, readers must either have no preferred explanation, or must accept the simpler of the two explanations: That the Cerutti Mastodon site, like the other two, is the product of geological processes and/or heavy machinery.

All this doesn’t mean that the Cerutti Mastodon site is not, in the end, archaeological. We shouldn’t reject a claim because there are other potential explanations, but neither should we accept it simply because those alternative explanations have not been shown to be true.

All that is needed to force us to be agnostic about a claim in archaeology, or to prefer another one, is to show that there are other potential explanations that have not been adequately ruled out. It is then up to those making the claim to help us rule out the alternative explanations.


Braje TJ, TD Dillehay, JM Erlandson, SM Fitzpatrick, DK Grayson, VT Holliday, RL Kelly, RG Klein, DJ Meltzer, TC Rick 2017. Were Hominins in California ~130,000 years ago? Paleo-America 3: 200-202.

Ferraro JV, KM Binetti, LA Wiest, D Esker, LE Baker, S Forman 2018. Contesting early archaeology in California, Nature 554: 479-483).

Haynes G 2017. The Cerutti Mastodon, PaleoAmerica 3:196-199.

Holen SR, TA Deméré, DC Fisher, R Fullagar, JB Paces, GT Jefferson, FM Beeton, RA Cerutti, AN Rountrey, L Vescera, KA Holen 2017. A 130 000 year old archaeological site in southern California, USA, Nature 544:479-483.

Holen SR, TA Deméré, DC Fisher, R Fullagar, JB Paces, GT Jefferson, FM Beeton, RA Cerutti, AN Rountrey, L Vescera, KA Holen 2018. Replying to JV Ferraro et al, Nature 554.

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