Hominid Hunting, Pinnacle Point, and Me. An epilogue.

Hominid Hunting has just covered the latest news from Pinnacle Point, the subject of yesterday's blurt. I couldn't let it go without comment. Hell, I think by now the author, Erin Wayman, probably expects it!
     It's 'awaiting moderation' as I write this. However, in case it's considered too technical or too contrary for publication, I'm gonna quote myself here, verbatim. Here's how it goes.

Hi, Erin. Pinnacle Point is quite an amazing archaeological locality. And the excavators, Brown and Marean, are doing excellent work. I know that it'll sound a bit like sour grapes, however, for years now there have been those who question not the finds, but the age estimates of these and other southern African sites. Like those at Pinnacle Point, the spectacular finds derive from caves, where organic preservation is often enhanced either by protection from the elements or the chemistry of the cave environment, or both. Unfortunately, for those parts of the site that are beyond the radiocarbon limit—around 40,000 years—the excavators have relied on less precise dating techniques. One in particular, optically stimulated luminescence (OSL), begins with the assumption that a given grain of quartz sand was exposed to sunlight for a time before final burial in the cave. Where caves are concerned this assumption is an untenable assumption, because no one is able to say ahead of time, with any certainty, that a single grain was or wasn't exposed to sunlight sufficiently powerful or for long enough. As a result, once the technique has yielded its raw results, there follows a complex mathematical dance based on all sorts of other assumptions, as a means of 'eliminating' the uncertainty of whether or not a given quartz grain had been sufficiently exposed to sunlight. Moreover, if the mathematical assumptions and the inherent complexity of the calculations are going to be in error they'll always overestimate the time since that quartz grain (and the artifacts in proximity that are of interest) was last exposed to sunlight. Logically, there's no under-estimating ages in caves using OSL. This leaves us with a question, one that I think the excavators of Pinnacle Point and elsewhere cannot logically escape. If the dates of unequivocally modern human behavior elsewhere in the world are less than about 45,000 years old, what are the odds that the anomalously early dates for similar behaviour in those southern African sites—all dated by OSL—are systematically overestimating their age? I'd say those odds were far better than the likelihood that all of the finagling involved in arriving at an OSL age estimate is yielding accurate and precise chronometric results.
[Update 0045 UTC November 10, 2012: Doh! I knew I was forgetting something! The bedrock in which the Pinnacle Point caves are developed is described as quartzitic. Wanna know how long it's been since the quartz grains in the bedrock last saw sunlight? Your guess is as good as mine. Suffice it to say that it's unlikely that they had been exposed to very much sunlight once they fell to the floor. All that matters is that the uncertainty introduced by one minimally exposed grain would introduce one hell of a wrench in any age estimate, even one that's been through the math mill.]  

I think that about sums it up. Now, why couldn't I have said that yesterday?

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Throwing in the Towel Thanks to Pinnacle Point, South Africa. As If.

At home. Under the weather. What else to do but watch the news ticker. It is ablaze with the latest news from Pinnacle Point in South Africa. The first word I had of it was a headline about this piece, just published, in Nature. 

In the article, long-time acquaintance and Mousterians 'R' Us advocate Sally McBrearty extolls the collection of more evidence for modern human behaviour at around 70,000 years. Sally was commenting on a Letter to Nature also published electronically yesterday. 

As you know from reading the SA, there are plenty of claims out there for modern human cognitive abilities or behaviours, or both, going well beyond 100 ka--blade industry at Kathu Pan 1 and Qesem Cave; hafting with bitumen or birch tar, and so on. However, as you also know, I've been critical of a great many of them. 
     Yet, according to the age estimates for unequivocally modern human activities at places in southern Africa, such activities are occurring at an age anywhere from 30 ka to 60 ka earlier than they do in Europe and southwestern Asia. For example, finds of decorated ochre and pigment processing 'kits' at Blombos Cave ca. 75 ka. In today's piece by Brown et al. we're hearing about use of the bow and arrow ca. 70 ka [I haven't had the time to examine the actual evidence for the claim other than to note that they refer to the microlithic portion of the assemblage consisting of small backed blades.]. This of course is one of the inferences frequently made for the kind of stone tools comprising the Howieson's Poort phase of what in Africa is called the MSA (Middle Stone Age). 

PP5-6 excavation. Deeply stratified and sharply inclined, much like a cone of talus [Credit: Erich Fisher; (inset) Simen Oestmo] © Science/AAAS.

     
I've previously said quite a bit about these early dates, here and here. However, this latest publication, and an earlier one from the same [or similar] group of authors, published in Science a few years back  claims [and at this point I have no reason to doubt them] that they have evidence of heat treating lithic raw material to make it more workable, between about 70 ka and 164 ka! This would be a great discovery even if a mere 30,000 years old. Unfortunately for me, these two inferences--of bows and arrows and heat treating--leave me with a new emotion--dismay--at the precocity of the ancient southern Africans. That's because these microliths and heat-treated lithics from Pinnacle Point derive from a part of the Pinnacle Point locality known at PP5-6, which is generally described as a rock shelter.

Pinnacle Point PP5-6. Tarpaulin covers the excavations. © Science/AAAS.

      In my earlier rantings I suggest that using Optically Stimulated Luminescence (OSL) age determinations drawn from buried cave sediments may be the culprit, artificially overestimating the age of these patently modern human assemblages. That's because there's really no way of knowing, a priori, whether or not an individual quartz sand grain had ever been exposed to the sun, much less for how long. [This, you'll remember, is a crucial assumption of the technique.] It's this uncertainty that causes OSL experts to undertake what appears to me to be a complex series of calculations and extrapolations designed to overcome the potential shortcomings of the technique. However, a rock shelter is a bit stickier. Presumably a rock shelter would be exposed to sunlight year in and year out, and thus you might imagine that any quartz grain that came to rest there had been exposed to sunlight long enough to have its 'clock' set to zero [unless, of course, that grain had been stripped from older deposits, redeposited in the rock shelter and immediately covered by sufficient material to preclude its being affected by the sunlight thereafter--like, perhaps, at night]. Now, after about a day and a half of off and on Googling I've been able to sight nothing written that describes the geomorphic history of PP5-6. Nevetheless, I have a hypothesis that will allow me at least some peace of mind. Given its proximity to a series of true caves at Pinnacle Point, and given its location at the edge of the escarpment that contains those caves, it seems highly likely that, while exposed today, the sediment accumulation at the site occurred inside a cave in which the roof and shoreward wall have subsequently collapsed and migrated down slope.
   So, unless I'm mistaken, I have no more reason to accept these early dates from the Pinnacle Point locality than I do the others from caves in South Africa. I know that the Very Serious Palaeoanthropologists like Curtis Marean will simply scoff at my scepticsm. Nevertheless, one can't help but wonder. And one day, perhaps, someone will try to directly date a piece of bone from one of those amazingly old stratigraphic units and Voila!
     I live in hope. No. Scratch that. As John Cleese's supine character in Clockwise moaned, 'It's not the despair...It's the hope.'

   
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Why No 14C Dates for Blombos Cave's MSA? Not Lobbing Aspersions. Just Sayin' ...

If I were a chess player I probably wouldn't be trying this gambit. But I'm not. So, bear with me.

Worked bone, stone and ochre from Blombos Cave (Wikipedia)

I need help with a question that's been nagging me for years. I'm curious to know if any of the bone artifacts from the Middle Stone Age (MSA) layers at Blombos Cave have been directly dated using AMS 14C. From my reading it appears not. In fact, it looks as if 14C was abandoned in favour of luminescence techniques once they had excavated deeper than those layers identified as Late Stone Age, the earliest of which were dated to give-or-take 39 ka BP. Everything below that is deemed to be MSA, and organic materials such as charcoal and bone were passed over in favour of grains of sand or burned flints in those strata. 
     Remember that, for most of us, MSA is synonymous with the Middle Palaeolithic in the rest of the world, and, for better or worse, it's exclusively associated with the Neanderthals and their ilk, for which the jury is still out as to their cognitive equivalency with us modern types. Finding what are clearly modern human artifacts at Blombas Cave and elsewhere on the order of 30 to 50 ka earlier than anywhere else in the world has stunned and amazed scientists from Barrow to Burbank. But it's never sat well with me. 

Location of Blombos Cave, South Africa (Credit)

     You and I know that 14C is perfectly capable of accurately gauging the age of organic materials until at least 50 ka, notwithstanding the need for calibration that corrects for environmental  and other effects. Why then do we have only luminescence age determinations for the sediments in which the Blombos Cave bone artifacts and charcoal were deposited? Henshilwood et al. (2002) provide some insight, although I'm not certain they realize that by doing so they've left themselves exposed to (at a minimum) questions about their decision.
     That (to me) curious decision is explained in what amounts to a throwaway comment, which I will quote here

In radiocarbon terms, the MSA at BBC is of infinite age (Vogel, personal communication).

The MSA levels are being dated using luminescence techniques: single-grain laser luminescence (SGLL), single aliquot optically stimulated luminescence (OSL and IRSL), multiple aliquot OSL on sediments and also TL of burnt lithics and electron spin resonance (ESR) of teeth (Henshilwood et al. 2002:638). 

Being the skeptical type, I was intrigued by what seemed to me to be such a weak citation as to the inefficacy of 14C beyond 39 ka--the date of the oldest LSA at Blombos. Just a 'Vogel pers. comm.' No reams of empirical evidence. No other justification. So I endeavoured to discover by what authority Vogel had made such a pronouncement.
     No doubt some among you will think it naïve of me, or worse, that I'm poorly informed and ill-prepared to be taken seriously by the palaeoanthropological establishment. Nevertheless, I had no prior knowledge of Vogel's reputation in the radiocarbon world and in the South African archaeological community. His work includes a 1997 paper in Radiocarbon in which he attempted to calibrate 14C dates with U/Th dates within the same stalagmite from a South African cave. That work was superseded a few years later by the more widely cited Fairbanks et al. (2005), who honed the 14C calibration curve back to 50 ka using pristine corals from around the globe. Their findings are that 14C underestimates calendar years such that 45 RCYBP works out to 48,934 calendar years (give or take 500). By this means the calendar date of 39,200 BP from the lowest LSA level at Blombos would have been produced by a radiocarbon age of about 34 ka RCYBP (try it yourself by clicking here to go to Fairbanks's calibration calculator).
     It would seem, therefore, that despite Vogel's pronouncement, cited in Henshilwood et al. (2002), there is no physical limitation on dating organic material that is older than 39 ka (i.e 34,000 RCYBP), as long as its age doesn't exceed 45 RCYBP. That would, theoretically, allow the excavator of Blombos Cave to extend use of 14C for at least a further 11,000 RCY beyond the earliest LSA from Blombos Cave. Surely some of the MSA materials could be presumed to date from this 11,000-year window.
     Directly dating the bone and charcoal from the upper MSA strata may prove nothing. However, knowing that there's no theoretical limit on the use of 14C for that 11,000 year period leaves wide open the question as to why Chris Henshilwood hasn't attempted to date, directly, some of his bone artifacts or charcoal from the MSA layers. It's just possible that they would yield dates far younger than those produced by luminescence techniques (about which I've had a certain amount to say in previous efforts here at the Subversive Archaeologist).

From Henshilwood et al. (2002)

     After all, the MSA levels in Blombos (at least those illustrated in Henshilwood et al. [2002], shown above) appear to be quite shallow--the sort of depth that you could imagine accumulating in far less than the 35 ka that the luminescence dates would have you believe it took for them to accumulate--and it's within reason to suspect that they could easily have been deposited in the 11 RCY or so before 39,200 BP.
     And so. For what it's worth, I'm issuing a challenge from this lofty perch of mine. Chris, try dating some of your MSA bone using good, old-fashioned, AMS 14C and see what you get. A fair few of us are curious to know the result. 

The 'MSA' and Modern Humans: It's Only a Matter of Time

What counts is not what sounds plausible, not what we would like to believe, not what one or two witnesses claim, but only what is supported by hard evidence rigorously and skeptically examined. Extraordinary claims require extraordinary evidence.  — Carl Sagan 

BBC: Blombos Cave PPC: Pinnacle Point Caves KRM: Klasies River Mouth Cave

The southern African publishing machinery is in high gear when it comes to the so-called Middle Stone Age (MSA). It feels like there's a new claim every week. In this case, similar claims've been made before. But this time it's for ... are you ready for this? It's a big surprise, I know. But this example is...wait for it...Yes! The oldest piece of worked ochre ever reported! A-bloody-mazing! Those MSA people were modern humans for sure! And they were damned good at it, too, if I'm any judge! More on the ochre after I tell you why I'm telling you this.

     All the evidence points to these discoveries being the work of people like us--the skeletal remains from Klasies River Mouth at 75 to 125 kya (modern human, chins and all!), the Howieson's Poort stone artifacts at Bombos Cave and elsewhere from about 65 to about 60 kya (to all intents and purposes like the Mesolithic of Europe with its backed blades), the beads, the ochre, pigment grinding tools, and more. 
     The MSA of southern Africa is nothing like the Middle Palaeolithic of most other regions. Quite simply, while the Neanderthals and skeletally modern humans in Europe, southwestern Asia and northern Africa were still hacking flakes off 'Mousterian' bifacial cores [or handaxes, if you prefer], sometimes taking smaller flakes off the edges to keep them sharp, and trying to rejuvenated their bifacial cores with a prepared platform and a might whack intended to split the core in two (often only resulting in the removal of just a final flake--a 'Levallois' flake [if you prefer]), the MSA people of SA were acting just like you and I would have (minus all of the industrial culture accoutrements like white wine [most likely] and Saturday morning cartoons on TV).

Howieson's Poort lithics (Image credit)

    What to make of all this really early 'industry?' It's not a trivial point. As far as the archaeological record of the rest of the world goes, these people, at 100 ka and more, were upwards of 60 ka ahead of the cultural curve of the rest of the world. So it's an untrivial, and still open, question what kept people like us from doing, in the first 60 ka of modern human history, what members of the same species evidently did in an instant of geological time once we stepped outside of Africa. Let's face it, after about 40 to 50 ka ago it was like modern humans were shot out of a cannon. Australia was reached in the blink of a geological eye. Europe? Same story. Eastern Asia? The same. And during an ice age, no less. Eat your hearts out, Homo erectus! Homo sapiens rules!

     As you might imagine, I'm troubled by all this precocious behaviour on the part of antipodean Late Pleistocene southern Africans. It's a conundrum that I can't get out of my head. And every time a new claim comes down the 'pike I get more irked by my inability to explain it, or even to conjure up a plausible scenario. Believe me, this enigma is nothing like the other stuff that irks me [of which you're all aware by now]. This is us--unequivocally modern--but it's us when we shouldn't be there. I know. I know. That's not scientific, Rob. You should have an open mind. [That's all well and good, but an open mind isn't the same thing as an empty one--I need an answer, not a reminder of my shortcomings!]
     I'm confused, too, about use of the term Middle Stone Age for what is obviously the work of both skeletally and behaviorally (and cognitively) modern humans. Someone in the know might be able to help me here [if I could get the bleeping comments to work again!]. Is it called MSA because it's older than a certain arbitrary cut-off on the geological time scale? Why don't they just call it 'Earliest Upper Palaeolithic' or something like that? Somebody please explain!
     All of this very early modern human evidence from southern Africa reminds me a bit of the myriad claims for Pre-Clovis occupation of the Americas that have been erected, assailed, and finally collapsed under the weight of skepticism that usually accompanies such assertions. The artifacts are real. The dirt's real. But something's always wrong with the dates [except, perhaps, Calico Hills, where the eye of the beholder was just too clouded by its infatuation with broken rocks to see the forest for the trees]. That's the way it always ends, with a dying fall. The claims, one after another, are justifiably questioned. No resolution. But the claims fall by the wayside, and no one makes an effort to get them back in the mainstream. It's happened over and over and over again. My strong suspicion is that it's happening in South Africa, but without the questions, without the doubt. And that, alone, worries me, and suggests that there's a systemic problem.
     I have a fearless prediction. One day either the late dates for everything outside of Africa are going to be shown to be too young, or the inverse will prove to be the case. I think you know where my money is.
     One final thought. For years it's been the orthodoxy to think of the human lineage as having been on a slow march from ape-dom to humanity. You've heard it. Sure you have. For '99% of human history we were egalitarian hunter-gatherers.' [Stan: I remember you saying that in Old World back in '86--no shame implied. It has been the mantra for decades.] Then agriculture happened and we all went to Hell in a hand-basket and we ended up (some of us) Capitalists, and look where that's gotten us! [Ruth: I've always had a bone to pick with that one!]
     What if we weren't human until recently? In a way I think it lets us off the hook. After all, the first stone artifacts are 2.5 MILLION years old. If we've been thinking like we do now for 2.5 million years, I'd say we probably don't deserve to survive as a species, given the mess we seem to have made of things in just a few tens of thousands of years. BUT, if we only became human give or take 40,000 years ago, and if the first 30 of those were spent coping with an ice age, that means we've only had about 10,000 years to figure things out. I like that better. Because I think we're better than the long chronology paints us. I like to think that we've come a LONG way in 10 ka.   
     Think of it. Domestication at give or take 10. Cities and monumental architecture, art, writing, by, say, 8 or so. Philosophy, drama, mathematics, geometry, science, by 4 or so. I mean, if you look at it from the short chronology point of view, we look a lot better. I'd hate to think that we'd been at this whole human thing for 100,000 years.
     We'd seem REALLY pathetic.


Back to the ochre that persuaded me to write the above. With all due respect to Francesco d’Errico, Renata García Moreno, and Riaan F. Rifkin, authors of 'Technological, elemental and colorimetric analysis of an engraved ochre fragment from the Middle Stone Age levels of Klasies River Cave 1, South Africa' (Journal of Archaeological Science, 39, 942–952, 2012), I fail to see why this publication is so effing important. Imagine someone in Europe publishing this: 'Ooh, ooh, another piece of ochre from the Upper Palaeolithic of France!' They'd be laughed out of the academy--even if it were the oldest such artifact ever found. So, forgive me if I'm less than fired up about this amazingly complex and scholarly article about a lump of iron oxide with a bunch of scratches on it. Mind you, if the scratches spelled out the first five verses of Genesis, there might be a story there. Otherwise...yawn.

From d'Errico, Moreno and Rifkin 2012

I hope this, my attempt to explain more of my mystification with the MSA of southern Africa, hasn't kept any of you from your naps!
     Be well. Have a good weekend. Thanks for dropping by.