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Shellfish Engravings Mark the Rise of Man

Stephen Munro examines casts of Homo erectus.

Stephen Munro examines casts of Homo erectus, which was responsible for the 500,000-year-old engravings. Credit: Phil Dooley

By Stephen Munro

Digital images of ancient shellfish have revealed markings that, according to conventional wisdom, simply shouldn’t have been there.

While gathering data for my PhD in 2007, I organised a research trip to examine shells from early human fossil sites. My primary interest was whether mussels, clams, oysters and snails could reveal anything about the ecological characteristics of human evolution.

The trip took me to a university in Belgium and museums in Ethiopia, Germany and The Netherlands. It was at Naturalis – the Natural History Museum of the Netherlands – that I first encountered an engraved shell with the potential to reshape the way we view human evolution.

Curiously, I never noticed the engraving at the time. Only when I returned to Australia a month later and began looking through digital images from the trip did I notice a distinct set of lines on one particular shell. My immediate reaction was that this zig-zag pattern was the work of a human hand.

This was astonishing for a number of reasons. First, the shell was half a million years olds – more than 300,000 years older than what was widely considered the next oldest engraving of a similar nature. Second, the site from which the shell derived – Trinil, on the Indonesian island of Java – is synonymous with the species Homo erectus, and markings of this type had never been found in association with this species before.

Homo erectus, an early species of human, first appeared in the fossil record about 1.8 million years ago, and survived for well over 1.5 million years. It is often depicted as a primitive form of human, but it survived for much longer than our own species, Homo sapiens, has existed.

Homo erectus was first discovered by a Dutchman, Eugene Dubois, more than 100 years ago. Dubois was born in 1858, a year before the publication of Darwin’s landmark book On the Origin of Species. Therefore he grew up in a world where the idea of evolution through natural selection was a well-known and widely accepted concept. Inspired by Darwin and other naturalists including Ernst Haeckel, Dubois became fascinated by the idea of a “missing link” between apes and humans, and set out to find it.

Incredibly, Dubois was ultimately successful in his search, not so much in finding a “missing link” – an outdated term no longer used in evolutionary biology – but in finding a pre­historic species of human that pre-dated Homo sapiens. He named the species Pithecanthropus erectus, which we now know as Homo erectus.

The idea that somebody could set out to find a previously unknown fossil species, and actually achieve that goal, seems remarkable given how rarely fossil species are discovered. But Dubois’ search wasn’t completely in the dark. He believed – as Darwin and other naturalists did – that humans most likely originated in the tropics, and he also recognised the close relationship of humans and apes.

Although he was wrong in believing that gibbons may have been the closest apes to human ancestry (we now know that the great apes, and African apes in particular, are closer), his belief led him to consider Indonesia as a potential location for early humans. Indonesia also appealed because, as a Dutchman, Dubois was able to gain a posting via the Dutch army to what was then the Dutch East Indies, in order to search for his missing link.

In 1891 at Trinil, Dubois discovered the skullcap and other bones of what was soon dubbed Java Man. He later took the fossils back to The Netherlands, along with the fossilised remains of an array of other animals including elephants, tigers, monkeys, crocodiles and molluscs.

When I began my research into whether molluscs could reveal anything about the ecology of early humans, I had no idea if any molluscs were associated with early human fossil or archaeological sites. Traditional stories of human evolution generally focused on open habitats and the exploitation of large mammals, and most discussions and descriptions of landscape and fauna tended to reflect this.

I was interested in testing an idea that differed from the traditional narrative, emphasising waterside habitats as important places where humans may have evolved, and the role of waterside foods including bivalve molluscs such as clams, mussels and oysters.

While organising my research trip I was lucky that Josephine Joordens, a Netherlands-based marine biologist with an interest in early human ecology, had also recently become interested in the mollusc shells collected by Dubois at Trinil in the 1890s. I was lucky to meet with her and Dr Frank Wesselingh, a mollusc expert and curator at Naturalis, to look at these shells and discuss a research plan.

Our attention was drawn to a collection of large freshwater mussels that filled a number of boxes and included hundreds of individual shells as well as shell fragments. We were intrigued by the uniform size of the shells, virtually all of which were large, fitting comfortably in the palm of one’s hand. This seemed to indicate that this wasn’t a natural accumulation as we would otherwise expect small and medium shells to be present as well. The fractures on a number of the shells also seemed to correspond to a particular pattern that also seemed unnatural – as if they had been deliberately broken.

One way to test whether this collection included elements of cultural activity was to make a series of measurements and then compare these with other collections. But with limited time I had no way of undertaking such a time-consuming task.

As luck would have it, however, the next day in The Netherlands was a public holiday, and this provided me with an opportunity to use Wesselingh’s vacant office and photographic equipment to document the entire collection.

One of the interesting things about the discovery of the engraved shell is that although the engraving showed up clearly on the digital image, it was very difficult to see with the naked eye. Indeed, it had escaped the attention of discoverers, researchers and curators for more than 100 years. Even when I held the shell and placed it under the camera, I failed to see the engraving. The shell needs to be held in such a way so that the light catches it at just the right angle, and I was fortunate that my image captured the light in just such a way.

Many people have asked whether the engraving is an early example of symbolic art. It is difficult to know what the intention of the engraver was, or whether the markings are representative of some feature of the landscape or have some abstract meaning.

What is apparent is that the markings would have stood out much more clearly when they were freshly made, because the original shell would have had a dark layer of organic matter, providing a striking contrast to the white underlying shell exposed by the engraving.

So how does this discovery change what we know about Homo erectus, and what is its significance? First, it demonstrates a sophisticated ability of Homo erectus to understand the various elements of the world around it. The assemblage includes evidence that Homo erectus was opening the mussels by drilling a hole to sever the adductor muscle, which keeps the bivalve closed, revealing an understanding of the shell’s anatomy. They were also modifying the shells to be used as tools: clam shells can be extremely strong and sharp!

Homo erectus therefore, along with the ability to create a deliberate pattern, understood how to find and gather these shells, how to open them to gain access to the nutritious meat inside, and how to modify the shells so that they could be used as tools.

The discovery also adds weight to the idea that waterside habitats and shellfish especially may have been important elements in human evolution. Shellfish are a good source of omega-3 fatty acids, which are essential for healthy brain growth. The fact that Homo erectus had a significantly larger brain than apes might be explained partly because they were regular consumers of a good source of these brain-building nutrients.

The transition from a fruit-eater to a shellfish-eater is also easy to explain from an evolutionary perspective, given that certain shellfish such as mussels and oysters often grow on the roots and trunks of trees in areas where land meets water, and therefore can be plucked and eaten just like fruit.

And to gather shellfish from the water, various adaptations could be expected, such as bipedal wading, efficient tool use, an external nose with downward-pointing nostrils, a more linear body, nakedness and more fat below the skin. All of these features distinguish humans from apes, and all make sense given a scenario where shellfish-gathering was an important part-time activity for early humans.

One more feature that distinguishes humans from apes is our ability to talk. If early humans were spending part of their time diving in relatively shallow waters for shellfish, we would expect them to have developed more efficient breath-holding abilities and control of the airways. These are essential prerequisites for spoken language and, along with the larger brain, may partly explain why humans have the ability to speak while apes do not.

The discovery of a deliberate engraving on a shell associated with the very site at which Homo erectus was first discovered, while unexpected, does fit neatly with the model outlined above. Moreover, the results of my PhD show that large mussels similar to the ones found at Trinil were also associated with early human sites in Africa (Chiwondo, Turkana Basin and Olduvai Gorge), China (Nihewan), Europe (Pakefield and Ceprano), the Middle East (Erk-el-Ahmar and Ubeidiya), Pakistan (Pabbi Hills) and another early Javan site (Mojokerto). While this does not prove that these shellfish were being consumed by early humans, the combined evidence does suggest that the old theory that humans were relying solely on hunting and gathering from terrestrial habitats, while ignoring aquatic resources, requires some reconsideration.

Time and again in my studies I came across site reports that indicated the presence of edible molluscs, but these rarely rated a mention in the corresponding faunal lists and discussions on early human ecology, behaviour and diet. I hope this discovery encourages researchers to look more closely at this potential food resource and ecological indicator.

If nothing else, this discovery demonstrates that Homo erectus was not just a primitive human species on its way to becoming “us”; it was a species that was supremely well-adapted to survive within its particular ecological niche, and it did so by exploiting the available resources with efficiency, ingenuity and creative flair.

Stephen Munro is a researcher in the Australian National University’s School of Archaeology and Anthropology, and a curator at the National Museum of Australia.