Anthropology.net

Well, I feel somewhat vindicated. Remember the post where I criticized hominin cut marks from over 3 million years ago? Others have also had an eye of suspicion and have published their concerns in PNAS this week.

I was wrong in considering the croc marking differential to the cut marks. But I was not wrong in thinking they author of the original paper made the wrong conclusions. The authors of this new paper raise up an even more logical explanation, and carried out a more thorough analysis. Here’s part of their argument from the abstract,

“The Dikika research group focused its analysis on the morphology of the marks in question but failed to demonstrate, through recovery of similarly marked in situ fossils, the exact provenience of the published fossils, and failed to note occurrences of random striae on the cortices of the published fossils (incurred through incidental movement of the defleshed specimens across and/or within their abrasive encasing sediments). The occurrence of such random striae (sometimes called collectively “trampling” damage) on the two fossils provide the configurational context for rejection of the claimed butchery marks. The earliest best evidence for hominin butchery thus remains at 2.6 to 2.5 Ma, presumably associated with more derived species than A. afarensis.”

Trampling vs. Cut Marks (The image in A is courtesy of R. Blasco and J. Rosell. The images in B, D, and F are modified from McPherron et al.)

Looking back at the comment thread, I got a lot of flak. Aside from being wrong about the croc markings, I won’t deny that my post was inflammatory and incited a lot of the response. But many who know just a bit about the fossil and archaeological record, may find it extraordinary to believe australopithecines were using stone tools to extract food from flesh and bone from ‘indirect’ evidence. Of more concern was the lack of exhaustive exploration into other possibilities.

I remember as an anthropology undergrad one of my professors designed a hands-on experiment for us. If memory serves me correctly, this was for a zooarchaeology class. She acquired some beef bones from the local butcher and gave us stone tools. We were instructed to extract the marrow from the bones. We hammered the afternoon away.

Part of our assignment was to use different techniques and tools. We could cut, saw, abrade, chisel, etc. After the mess was done we compared our extractions from prehistoric samples. This comparative approach allowed use to systematically compare how we modified the bone to how possibly prehistoric individuals modified bone.

The authors of the current PNAS paper did something similar. The hypothesized that trampling could have created similar modifications as seen on the 3.39 million year old Dikika bones. And what did they do? Well they got some bone and experimentally setup some trampling experiments. As one would expect, cut marks would have a \/ shaped incision. Incidentally, the bones from Dikika show a \_/ flat bottom morphology. The authors write,

“Ninety-six percent of experimental trampling grooves display a broad-based, open cross-section with the aforementioned shape, versus just 4% of experimental grooves inflicted by simple (i.e., unmodified) stone flakes used to cut meat from bones. In addition, curvy and sinuous groove trajectories characterize nearly 70% of experimental trampling marks,compared with just 10% of experimental cut marks created with simple flakes (11). Together, these experimental results provide a robust actualistic context to evaluate illustrated marks F, G, H2,and I on DK-55–3 as high-probability trampling damage and not stone tool cut or percussion marks…”

I wonder what happened to good science?

What happened to the scientific method?

Did we not learn how to set up experiments and carry out analysis?

How can a paper make all the way into Nature and not exhaust all the possibilities?

These are not rhetorical questions. I am seriously asking it. I honestly feel that there is something rife in paleoanthropological studies lately. I must sound like a broken record to say yet again, too often are papers published in haste and for fortune and glory… All which compromise the validity & ethical responsibility of the science.

Domínguez-Rodrigo M, Pickering TR, & Bunn HT (2010). Configurational approach to identifying the earliest hominin butchers. Proceedings of the National Academy of Sciences of the United States of America PMID: 21078985

I don’t know who this is worse for, the editors & reviewers over at Nature or the authors of the article who can’t tell the difference between crocodile teeth markings and stone tool modification, nor raise the possibility. The paper, “Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia,” very confidently proclaims unambiguous evidence for,

“stone-tool-inflicted marks on bones found during recent survey work in Dikika, Ethiopia, a research area close to Gona and Bouri. On the basis of low-power microscopic and environmental scanning electron microscope observations, these bones show unambiguous stone-tool cut marks for flesh removal and percussion marks for marrow access.”

Butchered by early humans or eaten by crocodiles? Image: David DeGusta

Given that the said rib fragment, DIK-55-2, came from a prehistoric lacustrine site. These markings could have been produced by crocodiles. Crocs, if you aren’t aware of (ahem editors and publishing group) are very abundant in the Rift Valley — both currently and prehistorically. On top of that, crocs like to eat meat and scavenge. Yes its true, they are carnivores. Australopithecines were at most ominivores, with wide based teeth useful in grinding tubers and nuts. Crocs have more meat shearing, bone crushing teeth than 3.39 million year old stone tools, which there are none of at the moment.

Given that there really isn’t an archaeological record for Australopithecine tools, I’ll take a gander and say crocs like to eat meat and scavenge more effectively than A. afarensis could make and use said tools to butcher a large ungulate. They have been on this Earth for roughly 197 million years more than hominins have and they are really good at what they do… Again, probably better than a species of hominins who did not live in the Stone Age. It is just as likely (if not more) that the markings were produced by crocodiles just given the ecological context.

Now just how different at cut marks from crocodile teeth marks? David DeGusta, from Stanford University, compared and contrasted the two different markings using images from Njau and Blumenchine (2006) paper titled, “A diagnosis of crocodile feeding traces on larger mammal bone, with fossil examples from the Plio-Pleistocene Olduvai Basin, Tanzania,” to those published in the current Nature article. I’ve inserted DeGusta’s image into this post on right for your own inspection. DeGusta was also on Science Friday, discussing this possibility, with one of the article’s authors, Zeresenay Alemseged. What do you think? Do they look completely different or similar? Seriously, I am asking you to comment. I’d like to know what you see.

Personally I don’t see much of a difference. I agree that stone tools marks are more V shaped, while croc teeth are more pitted/rounded. But take this into light: tool use, especially butchery, is a very human behavioral trait. In their search to attribute this human behavior to a primitive hominin species who roamed 800,000 years earlier, to the era of Australopithecus afarensis, without considering another possible explanation, the authors and editors of Nature were somewhat foolish.

Many paleoanthropologists are in this mad rush to claim their precious find is the most human of hominins, so as to etch their name into the textbooks in rewriting human evolution, that they sometimes forget about doing thorough comparative science. And many publications are in this mad rush to publish the most human of findings, that they sometimes forget about thoroughly editing scientific works. Think that could be the case? I sure do… Why should we settle on secondary evidence for Australopithecine stone tools when none have been found yet, and when another possibility hasn’t been extensively exhausted?

McPherron, S., Alemseged, Z., Marean, C., Wynn, J., Reed, D., Geraads, D., Bobe, R., & Béarat, H. (2010). Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia Nature, 466 (7308), 857-860 DOI: 10.1038/nature09248

Yesterday, I got sent a video of paleoanthropologist Zeresenay Alemseged‘s talk at this year’s TED conference. Last year we all got introduced to Zeresenay Alemseged when he and colleagues published their report on Selam a.k.a. Dikika fossil. Selam is a 3.3 million year old Australopithecus afarensis child.Here’s some of the stuff I wrote about that fossil:

• Little ‘Lucy’ fossil found
• A critique of the juvenile Dikika fossil publication
• A faint whisper of reason on Dikika

In the TEDtalk, Zeresenay talks about looking for the roots of humanity in Ethiopia’s badlands, what he has found, and how Africa holds the clues to what makes us human. TED has a lot content on his talk, and why you should listen to him.