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Riddles in the Dark: Kent's Cavern and the earliest modern Europeans

For those that enjoy scientific disputes, this week a new one appeared for the Palaeolithic, hinging on the reliability of the date published last year for a diminutive human jaw fragment as the earliest European Homo sapiens. I have to say straight up that I am not entirely independent here, having worked on the site in question, Kent's Cavern (I looked at the Neanderthal artefacts), and with several of the individual researchers concerned. Additionally, the new research challenging the date is as yet unpublished, and is only featured based on a pre-press piece in ScienceNOW, so it's hard to comment in detail on their position. However, as this is an important site that I also have a bit of history with, I do want to talk about it.

Now a glitzy show cave with uplighting and large concrete walkways for the many visitors it receives every year, Kent's Cavern is one of the most important Palaeolithic sites in Britain, and also in Europe. Historically it was one of the very first places where 19th century scholars began to comprehend that the biblically-based timescales they'd been working to were severely compressed. William Pengelly, who excavated the cave between 1868-80, was a true archaeological pioneer, developing his own 3D recording system, defined by large numbering "prisms" of sediment-1 yard x 1 ft x 1ft- and the artefacts and bones they contained. His work at Kent's Cavern and elsewhere provided some of the pieces for the great Antiquity of Man jigsaw that was being formed by industrious and curious Victorians, by proving that humans had lived alongside extinct animals, and had done so for a very considerable time. There's a great photo here of one of Pengelly's co-workers during early excavations. Nothing like this view of the cave now survives, after years of development into a tourist attraction.

Because Kent's Cavern is such a large cave, there was still a fair amount of in-situ (preserved in its original location) sediments left by the early 20th century. This led others with an interest in prehistory to continue excavations at the site, including the Torquay Natural History Society, led by Arthur Ogilvie. One of the things dug up by Ogilvie in 1927 in sediments also containing lithics and animal bones was a small piece of upper jaw (maxilla), identified at the time as that of a modern human.  Since the advent of methods for directly dating archaeological material in the latter 20th century, the age of the this tiny fragment has been a target  because it was obvious from its position amongst distinctive Upper Palaeolithic tools and extinct Pleistocene fauna that it represented one of the earliest human skeletal remains from Britain, and possibly Europe. Results published last year (paywall) by a team from Oxford Radiocarbon Laboratory and the Natural History Museum which suggested the maxilla is anatomically modern and most likely dates to 41.5-44,000 years ago (kyr), are now being challenged in a new paper, to be published in European Journal of Archaeology, reported on in ScienceNOW.

From the perspective of the history of science, Kent's Cavern undoubtedly is a significant site. Yet it has a surprisingly scanty publication record, due to complications arising from its lengthy and erratic early history of research. There is no complete monograph for the site, and in fact very little raw data has been published at all, for example on the lithic artefacts. Publications on the cave, aside from the excavators' reports and recent dating papers, include several reviews of the archaeology and deposits (which mostly underestimated the complexity of deposition) and more recent geological investigations and detailed discussions of the archaeology.

Lithic artefact from Kent's Cavern (my photo)
I first became familiar with the site during my MA in 2003-4 when I chose to do my dissertation on the Late Middle Palaeolithic (LMP) lithic assemblage, that is stone tools made by late Neanderthals, which were from the 'Cave Earth' layer. When I expanded my research into this period to the rest of Britain for my PhD, I also included the site in my analysis. Kent's Cavern has recently become central again to current Palaeolithic research agendas because the archaeology it contained seems to cover the period between the last Neanderthals and the first modern humans in Europe, including skeletal remains and lithic artefacts.



On the ventral (inner surface) of the flint tool can be seen the fact that it was excavated in January 1934, at a depth of 15', in the Vestibule. This roughly corresponds to a date of 39-47 kyr BP based on bones from similar depth. The mandible was found several feet higher (photo my own).
It must be admitted that Kent's Cavern is a tricky site; like many of the 19th century sites I had to deal with in my thesis, it was not excavated with the same detail, care and level of recording which we would be using today. The two images of a flint artefacts from the cave show typical markings found on artefacts from many caves dug during this period; one may be lucky in having an accompanying archive, often that is not the case. At Kent's Cavern, Pengelly is rightly celebrated for his attempts at 3D recording which were way ahead of most other archaeologists of his time. Yet the sheer amount of material removed from the cave (7340 prisms!), and the resulting huge archive of boxes and notes is daunting. Furthermore, over time there has been the usual problem of curation decay: not all of the original collection survives (at least 1400 artefacts were recovered by Pengelly and over 250 by Ogilvie). The archaeology was also historically dispersed to many different museums; a philanthropic intention that nonetheless makes comprehensive analysis very difficult.

In 1989 an Accelerator Mass Spectrometry (AMS) radiocarbon measurement gave a date (uncalibrated) of 30,900 +/- 6900 years for the maxilla fragment, which broadly fitted contemporary models for the occupation of Europe by modern humans. Over the past few years however, it has been recognised that early radiocarbon methods are likely to have underestimated the ages of Palaeolithic dates, in some cases severely, due to remaining contaminants. A major project led by the Oxford Radiocarbon Laboratory and the British Museum has been attempting to re-analyse previously dated material, using a new ultrafiltration method, producing much cleaner samples, and in most cases, significantly older ages. The Kent's maxilla was an obvious choice to include, however the jaw fragment did not contain enough datable material. Instead the researchers produced a mathematical model to extrapolate from dates on animal remains excavated above and below it. These were identified through careful examination of the original records by Roger Jacobi, who had been working intimately with virtually every Palaeolithic collection in Britain for years (and who sadly died in late 2009). The result indicates that the maxilla is most likely aged between 41.5-44 kyr old, making it potentially the oldest Homo sapiens remains in Europe.

The radiocarbon dates from Kent's Cavern, showing the modelled date estimated for the maxilla (star) based on bracketed measurements of fauna stratigraphically above and below. Adapted by permission from Macmillan Publishers Ltd: Nature, Higham et al. 2011

Without having seen the new European Journal of Archaeology paper, it's difficult to be certain of the precise objections raised regarding this result. But the ScienceNOW coverage quotes the authors as questioning the reliability of the radiocarbon model that has provided the very ancient age for the maxilla. They suggest in particular that Ogilvie's excavations were careless, that the exact location of the jaw fragment and the fauna used to create the dating model is unknown, and therefore it may be impossible to ever know the maxilla's age. It is certainly true that Ogilvie's work did not match that of Pengelly in terms of recording. However, as the photographs above show, Ogilvie did record depth measurements on at least some of the finds, as well as taking notes, and the maxilla is recorded as a particular find in publications.

The new study also apparently claims that the artefacts/sediments may have moved since they were first deposited. In one sense, this is quite likely: the 'Cave Earth' sediment which was dug by both Pengelly and Ogilvie, and which produced the maxilla, formed over a very long period, and does not represent in-situ preserved layers equivalent to living surfaces. Instead, the deposits formed slowly, with many different processes acting to bring material, including the archaeology into the cave, in what can be described as a super slow-motion debris flow. This seems to be demonstrated when the locations of Middle Palaeolithic artefacts from Pengelly's excavations are plotted, as many are nowhere near the original area of the cave mouth, and were found well inside deep chambers and galleries. However, this depositional process, common in caves, would still produce a deep, if coarsely, stratified record.

Indeed, the dates on animal bones selected by their depth according to Ogilvie's records do descend as would be expected if there was a general match between stratigraphic location and age (see the figure from the Nature paper above). If there had been mass disturbance of deposits, I would not expect to see the clear linear trend in the dates. So if the depths recorded are reliably reflecting age, then using them to modelling a date for the maxilla should be reliable.

While the outcome of this research isn't quite as paradigm-shifting as suggested by one of the co-authors of the new paper ("What is at stake is the entire [prehistory] of Neanderthals and early modern humans in Europe.."), the age of the maxilla fragment is something we need to tie down, as there are just so few early modern human remains from this period. As the ScienceNOW piece mentions, we have anatomically modern human remains in Eastern Europe by c. 40kyr BP at the site of Peştera cu Oase, Romania. Additionally, as reported earlier this year, we also have the earliest Aurignacian (early Upper Palaeolithic) archaeology thus far dated as between  43,060–41,480 cal BP at Geißenklösterle, Germany (paywall paper); I think most researchers wouldn't suggest this was made by anything other than Homo sapiens. Furthermore, a stone tool industry termed 'transitional' and previously suggested as possibly Neanderthal (the Italian Uluzzian), has recently been suggested to be made by modern humans, and is been dated using a new method on shell carbonates to 45,000–43,000 cal BP [thanks to Tom Higham for pointing it wasn't ultrafiltration, as I originally wrote!].

So a modern human reaching Britain c. 41,500 years ago-  the minimum date for the Kent's fossil suggested by the 2011 paper- fits the picture; even using the maximum age of c. 44 kyr would not be outlandish.  On the other hand, if the new paper is correct in its criticism (and we need to see it published first), then do things really change that much? There is solid evidence that Homo sapiens was already in Germany at this time (and possibly Italy too), only a few hundred miles from Britain. I'm certainly interested to see the new research, given that the authors have utilised the same archive material as the Nature study, but come to very different conclusions. Is there a question simply over the maxilla's depth? Or are they questioning the modelling more broadly? This debate certainly illustrates the tough job Palaeolithic archaeologists face in working with material from very old excavations and collections. Even when we have scientific methods to apply, painstaking reconstructions of old archives are still fundamental to our research. While ever greater sensitivity in dating can refine our models of human evolution, 100 year old handwritten records and sketches can only provide so much information, and will always be subject to re-interpretations and challenges.



Comments

Mischna Ong said…
I'm fascinated with archeology. Besides that, the equipments they use are so excellent that they can actually tell time and about the world and its making.

-Mischna Ong
Anonymous said…
Come to think of it, archaeology's actually harder than it look like. Archaeologists don't just find stuff; they study these and discover new facts only with the use of proper equipments.

| Molly |
Hi Mischna and Molly,

Thanks for your comments! Yes archaeology is pretty cool, it's amazing the different kinds of information we can now find out about past people's lives. So many new techniques have been developed over the pasy 30 years, we're still catching up with what we can do!
Anonymous said…
These experts can trace or track down what happen or how is life in our past society. Without archaeology, we would know little or nothing about the use of material culture by humanity that pre-dates writing.

Bradley Roy

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