This Argument Has A Few Holes In It. 80-odd-Thousand-Year-Old Shell Beads From La Grotte des Pigeons, Morocco and Blombos Cave, South Africa

Grotte des Pigeons in eastern Morocco, near the village of Taforalt. Photo by Abdellah Elbadaoui (Panoramio/GoogleEarth).

As I continue to wend my way through the literature I’ve missed during my absence from palaeoanthropology, I’m forever discovering scholarship that makes me think I’m on the other side of Alice’s looking glass. Yesterday, while nosing around in search of background knowledge for the Subversive Archaeologist, I found another beaut that I can’t ignore. And today I found it a companion. The two articles concern recovery of perforated marine shells from about 80 ka at the site known as Grotte des Pigeons [pictured above], near Taforalt in Morocco and at Blombos Cave, in South Africa. Of greatest interest to me is the way the authors attempt to rule out natural processes in pursuit of an explanation for their presence in the caves.

I hope to show why their efforts are insufficient, and why we should treat with caution these claims for modern human behaviour at such early dates. Remember Rule #1? Rule out natural site formation processes before invoking human or hominid activity. Its corollary is this: to rule out natural processes you need to keep in mind that different processes can result in similar archaeological ‘signatures.’

For example. Remember Raymond Dart and the “osteo-donto-kerartic culture” of the australopithecines? Dart had observed the behavior of members of traditional societies in southern Africa. He noted that when attempting to extract marrow from the long bones of their prey, they employed what Dart referred to as “the crack and twist” technique. The marrow seeker would strike the shaft hard enough to crack it. Then, grasping one end in each hand, the hunter would twist the ends in opposite directions until the shaft broke open. On the basis of these observations Dart proposed that the presence of similarly broken fossil bone meant that the Australopithecines had been hunting, then cracking and twisting the long bones to extract the marrow. It was many years before someone pointed out that the same effects can result from carnivore modification, and that it was much more likely that the presence of bones broken in that way was the result of carnivore behavior, rather than that of small, bipedal apes. Dart had premised his explanation on the only analogous process of which he was aware at the time. Such shortcomings permeate the archaeological canon. They remind us that we must always consider the possibility of equifinality—the idea that more than one process can result in a given set of observations. Moreover, to determine whether your observations are humanly or naturally produced, you need to involve as broad a range of present-day analogies as is possible. In the case of Grotte des Pigeons and Blombos Cave, the archaeologists have posited evidence that is sufficient to explain what they recovered, but their evidence is by no means the only possible explanation, nor necessarily the most parsimonious. At best their evidence is equivocal [a accusation that I’ve used over and over again in my work].

Enough preaching. On to the sea shells.

At La Grotte des Pigeons and at Blombos Cave excavators recovered small marine invertebrate remains that were altered from their natural state. In all, 13 were recovered from Pigeon Cave, and 41 from Blombos. The shells are perforated, and some bear a polish, which, the authors propose, you might expect if these objects had been strung like beads on a necklace. In addition, some very small patches of iron oxide were found on a few, which suggests to the authors that the putative shell beads had been artificially coloured with ochre. In the illustrations below you see the entirety of the collection from La Grotte des Pigeons. [I’m impressed by the presentation—for each artifact all six aspects are illustrated. Compare this to the artful display of the Blombos shells, further down, which is arranged so as to illustrate the path through which some twine might have passed.]

When viewing these images, keep in mind that the shells themselves measure about one centimeter across and slightly more in the longest dimension. Thus, the perforations are on the order of 500 microns in diameter. Note also that a great many of the perforations are irregular, and look more like they’ve been broken open rather than having been drilled.

From Bouzouggar, A., N. Barton, et al. (2007). “82,000-year-old shell beads from North Africa and implications for the origins of modern human behavior.” Proceedings of the National Academy of Sciences 104(24): 9964-9969. Specimen 14 is a modern-day individual.

The photo montage below seeks to illustrate the areas of ‘unnatural’ polish and other markings on several of the Pigeon Cave shells. The authors claim that these are likely to be the result of having been strung like a strand of … well, beads. I’d have to say that these aren’t patterned alterations.

From Bouzouggar, A., N. Barton, et al. (2007). “82,000-year-old shell beads from North Africa and implications for the origins of modern human behavior.” Proceedings of the National Academy of Sciences 104(24): 9964-9969. (Scale bar: A, C, E, and G = 1 cm; B, D, F, and H = 500 mm [sic].) [They must mean microns.] 

The photomicrographs below illustrate the red oxide on some of the putative beads from Pigeon Cave. The reddish material adhering to some of the shells from the cave was chemically characterized as hematite. Hematite is also known as ochre. As I stated above, there appears to be little rhyme nor reason to these alterations.

From Bouzouggar, A., N. Barton, et al. (2007). “82,000-year-old shell beads from North Africa and implications for the origins of modern human behavior.” Proceedings of the National Academy of Sciences 104(24): 9964-9969. (Scale bar: A, C, E, and G = 1 cm; B, D, F, and H = 500 mm [sic].) [They must mean microns.] 

At Blombos Cave the story is much the same. Total number is larger; different species; similar alterations. And I would make the same statement again: beyond the mere presence of fenestrations, their morphology and other modifications to these shells is hardly what I’d call patterned.

Henshilwood,C., d’Errico, F., et al. (2004). “Middle Stone Age Shell Beads from South Africa.” Science 304:404. 
Fig. S1. (A) Juvenile (1), sub-adult (2-4) and adult (5) Nassarius kraussianus shells from the modern biocenosis of Duiwenhoks estuary (Cape Province, South Africa) showing gradual size increase and thickening of the lip (solid line). Blombos MSA beads (R) are all made on adult shells (scale bar, 1mm). (B) Perforation types observed on N. kraussianus shells from modern and archaeological collections. The shaded area indicates the variability in hole locations. Types 6 and 8 on the dorsal side, found respectively on 63% and 24% of MSA beads, are observed on 2% and 3% on natural shells (N=2587) from Duiwenhoks and Goukou River estuaries. Type 1 on the ventral side (P, Q), produced by the predator Natica tecta, is present on 60% of shells from modern thanatocoenoses (N=1836) and absent on MSA beads. (C) Perforations on the dorsal side of dead N. kraussianus from the Goukou estuary. (D-I) Macro- and SEM photos of use wear on two MSA N. kraussianus shells (E,H, scale bar, 1 mm; F,I, scale bar, 500μm). (J-O) Macro- and SEM photos of a modern (J-L) and LSA (M-O) N. kraussianus shell showing absence of wear facet on lip (K, scale bar, 1mm; L, scale bar, 200μm; N, scale bar, 500μm; O, scale bar, 200μm). (P-Q) Ventral aspect of a modern N. kraussianus with hole drilled by Natica tecta (Q, scale bar, 500 μm). (R) Perforations on two orange MSA N. kraussianusshell beads from Blombos Cave (scale bar, 1 mm). (S) Typical white N. kraussianus shell beads with large perforations from Blombos Cave LSA levels. Verbatim from Henshilwood,C., d’Errico, F., et al. (2004). “Middle Stone Age Shell Beads from South Africa.” Science 304:404. 

So, at La Grotte des Pigeons and at Blombos Cave, archaeologists were compelled to interpret the origin and mode of deposition of these objects. I won’t suggest that they were grasping at straws to give these finds importance from an evolutionary standpoint. I’ll let you be the judge.

Both sets of authors use evidence from ethnography, natural history, or geology. For example, we know the shells don’t occur naturally in these caves. Simple enough. True enough. But, how do we assess their assertion that the shells could have been purposefully transported to these sites only by humans or hominids?

Likewise the perforations. The authors are aware that these tiny mollusks have mollusk predators that are able to drill through the shell and feed on the animal within. In the image immediately above, in P and Q, you see a hole drilled by Natica tecta. The Blombos Cave excavators note that such artifacts of predation show up 60% of the time in the natural death assemblages of this species. They also point out that they see none of these perfectly drilled fenestra in their archaeological sample. What are we to make of that?

Of the facetting noted on several of the shells, both sets of authors claim that these must have arisen due to repeated contact between either bead and bead on a string of beads, or between some form of cordage or other material and the beads that were strung on.

Finally, the ochre. What can we make of the microscopic presence of hematite on some of the shells from La Grotte des Pigeons?

Let’s take the transport agent to start with. Although the sea today splashes directly below Blombos Cave, that’s not so for Pigeon Cave. The sea was also more or less close to Blombos cave at 80 ka. Not so for Pigeon Cave. If the same transport agent moved the shells from the seashore to the caves, it was capable of moving them several tens of kilometers. So. Was it humans/hominids, or was it something else? I’ll admit that my efforts resemble more ‘back-of-the-napkin’ research than scholarly rigour, I was able to find at least one potential non-human transport agent capable of introducing such shells into the sediments at both caves—terns. Birds. The brown noddy [Anous stolidus] is known to collect such shells and incorporate them in their nests. The noddy is a tern. Terns occur throughout the world, and the brown noddy is native to South Africa and Morocco, as well as almost everywhere else in the world. How could one possibly rule out the possibility that these birds, or other occasional collectors, introduced these items to the archaeological context?

The authors would say that the nature and placement of the holes suggests human agency and the polish and traces of hematite support that conclusion. What about those holes? For starters, another quick trip to the internets tells me that at least two groups of animals are capable of boring through mollusk shell and that it is a commonplace the world over. The one below is riddled with tiny perforations caused by a species of sponge. Yup. Sponge. In addition, as you’ll have learned from the Henshilwood et al. paper, many species of predatory mollusks bore through other mollusk’s shells to get at the living creature within. You’ll be thinking “Yes, but the archaeological shells from Pigeon Cave and Blombos are not as beautifully regular as those left by sponges, or, for that matter by Natica tecta.” True enough. They appear to be ragged, not drilled. More on that after the pretty picture.

Far be it for me to accuse palaeo people of having a courser aesthetic sense than I, but the majority of the perforations claimed to be the result of human/hominid activity look as if they’ve been punched out by pressure applied either from the outside or from the inside. Who’s to say that those rough perforations weren’t the result of inadvertent pressure [underfoot, for example, or in pounding surf]? It’s logical to assume that pressure placed on a part of the shell where a sea creature’s boring had previously weakened that portion of the shell would be capable of punching out a larger hole. Damned difficult to choose. Don’t you think? Natural? Or not?

I realize that I’m merely casting doubt on the conclusions of the Blombos and Pigeon Cave archaeologists. Unlike the law, I can’t employ the ‘beyond a reasonable doubt’ criterion when I’m interpreting an archaeological site. But let’s face it. These claims are at best tentative, and would require, I believe, extensive experimental, ethnoarchaeological, and ethological examination before we accept them as fact.

Ooops. almost forgot. The polish. I think the presence of polish on just a few specimens should rule out any notion that they’d been strung like beads on a necklace. At a minimum the authors would want to examine ethnographic strings of similar or identical shells before claiming that the rare facets they find are due to rubbing of one shell against another on a string. Moreover, if such shells are susceptible to wear when suspended on a string, they can just as easily get worn on a beach that comprises numerous other such shells. After all, they all originated at the water’s edge. And, although the authors acknowledge that certain kinds of damage might be possible at the beach, their investigations of present-day death assemblages of these animals reveals to them that the modifications to the archaeological specimens are unlike those occurring on present-day strands. To that I would only say that time passes and circumstances change. What effect would over-harvesting of sponges have on the frequency of perforations on modern day mollusk death assemblages in Morocco? Or pollution in the Mediterranean? Or different substrates at different times at Blombos? I think you get my point.

And finally the ochre. Again, if ochre can occur in a cave at a distance from the ocean, it can occur at the sea-side.

For all of the reasons I’ve given here, it’s clear to me that the claims from La Grotte des Pigeons and Blombos Cave should be viewed with extreme caution, if only because they’re extreme claims for modern human behaviour at extreme time depth.

I hope you enjoyed this little road trip to the seaside. See you *cough* next time.

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A Human Evolutionary Battle of the Technological Titans for the Undisputed World Heavyweight Championship of Nest Building: Castor Canadensis VS. Pongo pygmaeus

Round 1: In which Pongo makes a nest (Credit)

In the world of ethology one group stands head and shoulders [well, head, anyway] above the rest–primatologists. Unlike their scholarly kindred primatologists can make a claim that’s unique among those who study animal behaviour. That is, they can always justify their days spent grunting, hooting and chest beating, and walking about on all fours so as to acclimatize their subjects to their presence by arguing that they are investigating behaviours that might [a mighty might, that] have a bearing on our understanding of how humanity dragged itself up out of the primordial muck savannah dust to stand erect and eventually to free its hands for tool making or rickshaw pulling and in the process enslaved its feet, qua pedal extremities, qua locomotory appurtenances, forever [credit goes to my old acquaintance Gary Richards for that bit of podial insight].

Jane Goodall in the early 1960s

     Indeed, since the time Dame Commander of the Most Excellent Order of the British Empire Valerie Jane Morris-Goodall removed herself from her (probably girlie) English roots to insinuate herself into Pan trogolodytes (chimpanzee) society on the shores of Lake Tanganyika at Gombe, revelations about the human-like behaviour of the great apes [other than humans] have punctuated an otherwise brutally hot, sometimes deadly, but always physically and emotionally difficult vocation. 

Gombe (© 2003 National Geographic Society. All rights reserved.)

Dame Goodall has shown us that chimps pull the leaves off of twigs to enable them to reach into termite mounds to attract termites for consumption [or did some oblivious ranch-hand inadvertently show one of them how to do it, resulting in a new ‘tradition’ amongst the group?]. Crumpling leaves to make sponges to extract water from puddles also emerged from the studies at Gombe [so, too, did brutal rape, torture and cannibalism of fellow anthropoids, but we won’t dwell on that. At least we can be certain that it wasn’t the same oblivious ranch-hand that taught them those things…].

     And yesterday comes fresh news of the startling cognitive capabilities of a great ape–Pongo pygmaeus, the orangutan. This animal is, by all accounts, something of a nest-building, evolutionarily precocious, civil engineer! van Casterena et al.’s ‘Nest-building orangutans demonstrate engineering know-how to produce safe, comfortable beds’ [published online before print April 16, 2012, doi: 10.1073/pnas.1200902109, Proceedings of the National Academy of Sciences of the United States of America (PNAS)] brings us face to face with … ourselves [albeit about 12 million years in the past]. Like the good anthropologists the authors are, they’ve thoroughly anthropomorphized this animal’s actions by deeming it ‘engineering’ and saying as much in print, in a scholarly journal [albeit one about which there are serious questions as to the seriousness of the review process]. This adds to the long list of claims made in behalf of science [the list I’ve just alluded to] for the other members of what’s come to be known as the Homininae,* the Linnaean Family that includes you and me.
But, before you get too caught up in the weltanschauung of willy-nilly anthropomorphizing that permeates higher primate studies, let me bring you back down to the ground. Remember this little furry rodent? Castor canadensis? They build ‘nests’ too! Only theirs are permanent, unlike those of primates [which are constructed from scratch at least once a day], and are sometimes fairly large structures. Did I say ‘fairly’ large?
One recently observed in Alberta is an incredible 850 metres long! That’s about half a mile! Have a look! Like the Great Wall, you can see this thing from space (thanks to Google Earth). These piccies are from a MailOnline article touting the [ahem] ‘engineering’ capabilities of this relatively small-brained, furry creature.

The brown area has been denuded by Beaver logging. The water flow is toward the top of the picture. The arrows point to two beaver lodges (themselves quite elegant feats of ‘engineering’). There must be myriad smaller ones, considering these ones, too, can be viewed from a satellite orbiting the Earth!

Giving credit where credit is due, the lead author of the orang nest article did say this in an interview.

‘We think the skills you’d need to build such a sophisticated nest are on a par with those you’d need to make and use tools, so require a similar cognitive ability. In this context, it would be interesting to investigate nest-building by other animals like beavers and birds,’ says van Casteren [click here for the full story of this quote].

I wonder what they’d conclude from a ‘study’ of the other nest builders. Chances are it won’t be that our closest relatives are on a par with beavers and bower birds. Nuh-uh. They’ll be lumping beavers and beaked dinosaurs with humans and the other great apes! I mean, really, what else can you say, on present understanding, than that most mammals are capable of some very complex behaviours, that are often, in part, learned from conspecifics. So, it seems, are birds. So are bees and mud wasps. So, too, are web-building spiders! If you wanted to take this whole anthropomorphic engineering meme to its logical conclusion, you could probably see evidence of cognition on a par with humans in the colonial habits of some single-celled organisms. Where does it stop?? 
     If I had my ‘druthers it would stop here, with the sensible conclusion that our closest relations are clever mammals. Full stop. Let’s face it, the nesting behaviours we’re witnessing amongst, for example, Pan and Pongo were probably extant at the time of the last common ancestor, so we’re not talking about some inevitable trajectory from nest building (however ‘clever’ it might seem to us primatologically impoverished humans) to modern human cognitive abilities–such as the ability to understand what these pixels are meant to mean to you. And even if we could possibly understand what it takes in the way of brain function to make a bloody orangutan nest, all we’ll have done is identify an ability that’s (conservatively) about 12 million years old. So. What!
     I think the study of our primate relations is important (if only ’cause they might not be around forever). But let’s get serious about the implications of what we observe.
     I’ll now go back to my torpid state.

* I, however, will continue to refer to this small group of extant and fossil forms as belonging to the Superfamily Hominoidea, and to the Families Pongidae, and Panidae, Gorillidae and Hominidae. Unlike so many of my siblings in the biological/physical anthropology clade of the academy, I’m not taken in by the vocal claims of the primatologists that certain behaviours amongst our closest genetic relatives makes them any more human than they were before Johnny Weismüller and Cheetah cavorted in the treetops together before Jane came along [all churlish innuendo intended!] Thus, I am not convinced by the recent, arbitrary revision of the Superfamily Hominoidea, and I will cleave to the taxonomy I’ve just outlined until either a) someone persuades me to think otherwise, or b) I expire.