In one of our first ‘Science Notes’, we discussed research happening at the Oxford Radiocarbon Accelerator Unit (ORAU), which was assessing the viability of compound-specific dating (see CA 336). Through this technique, instead of dating bulk material which contains a whole range of different molecules, a single specific compound is isolated and dated. This provides a higher level of confidence that the carbon being dated is actually from the specimen and not a contaminant. In particular, the team at the ORAU is using this technique to extract hydroxyproline from samples, an amino acid that is almost exclusively found in mammalian bone collagen. The successful use of this method is especially important for Palaeolithic remains which, due to their age, have some of the highest levels of taphonomic contamination (that is, they have been brought into contact with material from the burial environment).
At the time of the original article, this technique had successfully been applied to several Neanderthal samples from Croatia and Russia, showing that previous radiocarbon dates on these samples, which seemed to indicate that they were more recent – possibly overlapping with modern humans in these regions – were incorrect and that, in fact, these individuals were much older in date. Now the team from the ORAU and a group of researchers from across Europe have again applied this technique to Neanderthals, this time from Belgium, and once again the results have caused a re-evaluation of the timeline of Neanderthals in Eurasia. The results have recently been published in PNAS (https://doi.org/10.1073/pnas.2022466118).
With many caves yielding Neanderthal remains, Belgium is one of the key regions for studying the Middle to Upper Palaeolithic transition – the period when it is believed that modern human populations slowly replaced Neanderthal ones. Stratigraphic evidence from these caves had indicated that there was possibly a gap of around 4,000 years between Neanderthal and modern human occupation, but radiocarbon dating of some of these remains using the bulk collagen technique had instead suggested an overlap between these two populations, with a Neanderthal population possibly surviving into the Upper Palaeolithic. This would have meant that they may have been responsible for some of the ‘transitional’ technology (known as the Lincombian-Ranisian-Jerzmanowician, or LRJ, technocomplex) seen in this region, dated to around 36,000 BP.
To examine whether these dates held up using compound- specific dating, the team re-dated four samples from Spy Cave, as well as one sample from Engis Cave and one from Fonds de Forêt Cave, all in Belgium. In explanation for at least one of the previous dates that indicated a later presence in the region, the team found that one sample, a Neanderthal scapula from Spy Cave, had been heavily contaminated with modern bovine DNA – possibly as a result of being preserved with glue – which is probably why the sample appeared to be much more recent when using the bulk-dating method. As it is impossible to distinguish whether the isolated hydroxyproline from this sample had come from the actual Neanderthal or from the bovine collagen, this sample was deemed unable to be accurately dated. Two other Spy samples used in this study, however, were found mixed among a collection of faunal remains from the site during a reassessment of the collection, while the other was found on the slope below the cave in the early 2000s. This meant that these samples probably did not receive any conservation treatment and hence were able to be successfully dated.
Both the Engis and Fonds de Forêt samples also appeared to have undergone conservation treatment. For the Fonds de Forêt sample, however, non-animal-based treatments were used and the subsequent results indicated that the team had successfully extracted hydroxyproline from the intended sample. Regarding the Engis sample, instead of the contaminated bone, the team chose to use a molar from the same individual, which had not undergone any treatment.
After excluding the contaminated sample, the team found that all of the other samples yielded similar results, suggesting that the Neanderthals disappeared from this region of Europe much earlier than had been thought based on the previous radiocarbon dates, possibly around 44,200-40,600 calBP. These results now call into question the Neanderthal association with the LRJ technocomplex, as it does not seem likely that they were present in this region that recently. To confirm this, however, examples of LRJ technology found within these caves will need to be re-dated using the new methodology.
While it is apparent through DNA evidence that Neanderthals and modern humans did co-exist in Europe, and there is evidence in other parts of Europe for the arrival of modern humans as early as ~45,000 BP and possibly even ~47,000 BP, these new dates show the need for better and more precise dating from this period. Then we will be able really to home in on the specific appearances and disappearances of these two hominin populations.
Text: Kathryn Krakowka.