Why is it that practically every time there's a new discovery relating to the evolution of our own species, there is a headline saying that this finding 'could rewrite human history'?
Because, bingo! At least one newspaper report1, of a paper published last week in Nature, carried the header: "Homo erectus engraving could re-write human history, and might show art began 300,000 years earlier than we knew."
Now, the story's really interesting & surely didn't need the overblown headline, even if one of the research team was reported as using the phrase. Certainly the work of a large team of researchers (Joordens et al, 2014) has pushed back the dates for human use of symbols, to around 0.5 million years ago (on the basis of 40Ar/39Ar and luminescence dating), which is far older than the carvings and paintings of Cro-Magnons, and perhaps Neandertals - but doesn't necessitate a total rewrite of our history. And if their attribution of the finds to erectus is correct, then it extends our understanding of cognition in this species. (In fact, headlines like that fall right into the hands of creationists.)
This is a nice piece of detective work, & it also shows how serendipitous some discoveries can be: one of the team, Stephen Munro, noticed the marked mussel shell in photos he'd previously taken of specimens in a museum collection in Leiden, and that sparked a thorough investigation of the provenance and age of the shells. It turns out that the shell assemblage was originally collected at Trinil in Indonesia - the same location, and in fact the same strata (the 'main bone layer') as that of the 'type' specimen for H.erectus, collected in 1891 by Eugene Dubois. This led the team to the conclusion that this marked shell, and what looks like intentional damage to other shells, were the work of Homo erectus.
So what can we tell from these results? Well, it looks as if erectus enjoyed a good feed of seafood from time to time. The evidence for this lies in shells with holes in them - holes that lie over the position of the adductor muscle that holds the shell closed. Around 1/3 of the shells from this particular site had these holes, & overall the shell assembly contained "only large adult-sized specimens (about 80-120mm in length), while under normal conditions mussel populations contain all size classes" (Joordens et al, 2014): this strongly suggests that the molluscs were deliberately collected.
As for the holes themselves - the research team ruled out the possibility of damage by non-human predators, but noted that comparable holes were made in gastropod shells by pre-Hispanic modern humans living in the Caribbean. They went on to experiment on modern mussels and found that someone could use a tool such as a shark's tooth to drill a hole in the animal's shell over the adductor muscle; piercing the adductor caused the bivalve's shell to open. This speaks both to erectus' ability to conceive of and use rather smaller tools than we usually associate with them, and to their knowledge of shellfish anatomy. (You'd certainly find molluscs opened this way much easier to eat than if you had to bash them with a rock!) Another shell appears to have been retouched using a flaker, presumably for use as a scraper or other tool.
The team then looked at the geometric lines found on the outer surface of one shell & determined that they were highly unlikely to be due to the shell knocking around with other shells & stones, but were probably produced using a shark's tooth or something similar. The lines were most likely laid down while the shell was fresh & so covered with the coloured periostracum common to mussels, "which would have produced a striking pattern of white lines on a dark 'canvas' " (ibid.) The lines are quite deep, would have required a fair bit of force and also good manual control to make, and Joordens & her colleagues concluded that "a single individual made the whole pattern in a single session with the same tool" (ibid.).
So, we've got evidence of what may be the earliest known use of a shell as a tool; evidence of Homo erectus including seafood in their diet; and evidence of someone consciously & deliberately scoring lines in a fresh mussel shell. But was it 'art'? And does it really necessitate the rewriting of our entire evolutionary history?
1 I'm not sure why the Independent reporter correctly identified the engraved lines as being on a shell & then went on to talk about them being on 'a rock'. Poor subbing?
J.C.A.Joordens, F.d'Errico, R.P.Wesselingh, S.Munro, J.de Vos, J.Wallinga, C.Ankjaergaard, T.Reimann, J.R.Wijbrans, K.F.Kuiper, H.J.Mucher, H.Coqueugniot, V.Prie, I.Joosten, B.van Os, A.S.Schulp, M.Panuel, V.van der Haas, W.Lustenhouwer, J.J.G.Reijmer & W.Roebroeks (2014) Homo erectus at Trinil on Java used shells for tool production and engraving. Nature doi: 10.1038/nature13962, published on-line 3 December 2014