540,000 years ago | Trinil, Java

Homo erectus (Pithecanthropus erectus) shell engraving

You know that feeling, when something important ends up buried at the bottom of a suitcase, or forgotten at the back of a drawer? And you don’t get around to digging it out until more than a hundred years later?

Losing things, yes. Taking a century to find them again, perhaps not. And when those forgotten things include half-million year old shells drilled through with shark teeth, along with by far the earliest evidence ever found of symbolic markings, and to top it off they come from the same archaeological site where the first Homo erectus fossils were discovered, we’re in the realm of the highly improbable.

Enter Josephine Joordens, and the team at Leiden’s Naturalis Biodiversity Center.

Missing links

The Indonesian site of Trinil, in central Java, holds a special place in the history of palaeontology (the study of fossil bones). In 1887, Dutch anatomist Eugène Dubois had deliberately joined the army so that he could be posted to Indonesia, then known by its colonial name of the Dutch East Indies. A firm believer in the new science of evolution, Dubois was convinced that humans must have evolved in the Asian tropics, and this was his quickest ticket to a suitably hot place.

Dubois was also certain that there would be an intermediate form of human, somewhere between living apes and humans. The skeleton of such a missing link would demonstrate those differences to skeptics (even though the term ‘missing link’ actually had its origins in biblical schemes of a great chain of being, created by some form of God).

Dubois wasn’t the only person on an ancestral fossil hunt. But he was among the luckiest. Only a few years after reaching Java, his massive excavations along the Solo River at Trinil turned up not only the top of a thick skull, but a thigh bone and tooth. In 1892, Dubois triumphantly named them Anthropopithecus erectus (upright human-like ape), before upgrading them slightly in 1893 to Pithecanthropus (ape-like human).

Here’s a view of the 1890s Trinil dig. It’s the kind of large-scale project best achieved—as Dubois did—with an army’s help and forced convict labour:

When Pithecanthropus itself went out of fashion in the 20th century, the Trinil fossils were renamed to Homo erectus, and those Indonesian fossils are still the type specimens against which thousands of other global finds from the same species are assessed. Job done, Dubois returned home, and his intellectual hero Ernst Haeckel (who coined the word ‘ecology’ among many other achievements) hung an unflattering painted reconstruction of Pithecanthropus in his house:

A fascinating tale. But wait, weren’t we talking about shells?

As you can imagine, Dubois didn’t only find a few proto-human bones among all those tonnes of sand and soil. He also found other animal remains, including hundreds of freshwater mollusc shells of the now-extinct species Pseudodon vondembuschianus trinilensis. These shells, each around 6x10cm, were carefully packed and shipped back to the Netherlands along with the bones and other finds.

Where, over time, they got pushed to the back of a museum drawer.

Shell shock

Move forward a century, and student Stephen Munro was examining and photographing some of the Trinil shells in the Naturalis collection. One shell in particular stood out as an oddity: close up, it seemed to have a series of zig-zag lines deliberately engraved into its surface:

This kind of doodling is commonplace, almost subconscious, in humans. But it is exceedingly rare in the animal world. We don’t see even intelligent, dextrous animals like elephants going around scratching patterns.

Because of that rarity, archaeologists have tended to place a lot of weight on what these kinds of patterns might tell us about the minds that created them. For example, an engraved piece of ocherous shale from South Africa, about 77,000 years old, led its discoverers to declare that these cross-hatchings:

suggest arbitrary conventions unrelated to reality-based cognition…and they may have been constructed with symbolic intent, the meaning of which is now unknown.

That African team, led by Chris Henshilwood, even suggested that the marks could indicate that their makers shared a full, abstract language, in order to be able to discuss the ochre scratches. Have a look for yourself:

There are definitely some parallels between this ochre design, which is suggested to be a Homo sapiens construct, and the design on the Trinil shell from around half a million years ago, which was found with Homo erectus bones. The question is whether those lines are parallel enough to transfer the notions of ‘symbolic intent’ and ‘fully syntactical language’ onto our Asian human ancestors. That possibility has scared some archaeologists, who prefer an explanation where modern humans engraved the shell lines too, which could only be true if there was some complicated mixing of the soil at Trinil.

The Leiden team also found that some of the shells were probably used as tools themselves. And around a third of the shells had a precise hole bored through one end. The placement of those holes was right where you’d drill to weaken the adductor muscle that a shellfish uses to hold itself closed. In other words, the holes were evidence of a kind of early, natural can opener:

By experimenting with modern shells and the materials available to a Javanese Homo erectus, the scientists decided that the only logical drilling tool was a shark tooth. The same shark tool may also have been used for shell engraving, with strength and control needed to incise through the outer organic layer on a living mollusc. Back in 500,000 BC that outer layer—or periostracum—would have given a dark contrast to the pattern as the engraver exposed the lighter shell beneath.

The Trinil shell engraving sits at the intersection of many of the ambiguous aspects of tool use, whether animal or human. Their creator is disputed, partly because of preconceived ideas about the ability of a hominin some 500,000 years ago. We didn’t see the engraving happen, and we have a tiny sample, so maybe it was a fluke, or accident—the same arguments have been levelled at modern animal behaviour. For people who prefer to see humans as unique, rather than an unusual extension of the natural world, there will always be some excuse as to why a seemingly complex form of tool use must actually be simple, or unimportant.

Fortunately, evidence doesn’t usually care about intellectual turf wars or human biases. As with many scientific advances, only time will tell.

Further viewing: if you’re in the Leiden area, and Naturalis is open, the Trinil engraved shell and Homo erectus bones are on public display in the Early Humans Gallery. Or you can visit them virtually here (an English version is also available): https://www.naturalis.nl/en/virtualmuseum

Sources: Joordens, J. et al. (2015) Homo erectus at Trinil on Java used shells for tool production and engraving. Nature 518: 228–231. || Balter, M. (2014) Etchings on a 500,000-year-old shell appear to have been made by human ancestor. Science, https://www.sciencemag.org/news/2014/12/etchings-500000-year-old-shell-appear-have-been-made-human-ancestor || Kjærgaard, P. (2011) ‘Hurrah for the missing link!’: a history of apes, ancestors and a crucial piece of evidence. Notes and Records of the Royal Society 65: 83–98 || Alink, G. et al. (2016) The Homo erectus Site of Trinil: Past, Present and Future of a Historic Place. AMERTA, Jurnal Penelitian dan Pengembangan Arkeologi 34: 99-114. || Henshilwood, C. et al. (2002) Emergence of Modern Human Behavior: Middle Stone Age Engravings from South Africa. Science 295: 1278-1280.

Main image credit: Science Magazine, https://www.sciencemag.org/news/2014/12/etchings-500000-year-old-shell-appear-have-been-made-human-ancestor || Trinil excavation credit: Studying Homo erectus Lifestyle and Location (SHeLL), https://www.universiteitleiden.nl/en/research/research-projects/archaeology/homo-erectus-on-java || Pithecanthropus painting credit: Gabriel von Max, 1894, Ernst-Haeckel-House, Jena. || Shell engraving close-up: Wim Lustenhouwer, https://www.smithsonianmag.com/science-nature/oldest-engraving-shell-tools-zigzags-art-java-indonesia-humans-180953522/ || Ochre engraving credit: Henshilwood et al. (2019) || Shark tooth drilling credit: Joordens et al. (2015)