Wednesday, 3 September 2014

Neanderthal rock engraving

Important evidence for symbolic behaviour from Gorham’s Cave, Gibraltar

Archaeologists from the Gibraltar Caves project have found a rock engraving at Gorham’s Cave on the eastern side of Gibraltar. The deeply-etched cross-hatched pattern is carved into the dolomite bedrock of the cave, and was wholly-covered by an undisturbed archaeological level containing Mousterian artefacts. Thus its association with Neanderthals is secure.

The engraving is at least 39,000 years old and although modern humans were in Europe by that time, they had not yet reached the southern Iberian Peninsula. Furthermore, the Gibraltar rock engraving predates the earliest Aurignacian cave art, suggesting that it was an independent Neanderthal development.

Researchers carried out a number of tests to demonstrate that the engraving was intentional. They used a variety of tools and cutting actions on blocks of dolomite rock similar to the rock face at Gorham's cave and found that results best matching the engraving were achieved by using a pointed tool to create and enlarge a groove. Considerable care and physical effort was required to produce similar markings. The researchers also used the sharp tools to cut pork skin on a dolomite slab to rule out the possibility that the pattern had been produced accidentally while cutting meat or working animal hides.

The Gorham’s Cave rock engraving is only the latest in a series of recent discoveries that clearly demonstrate that the Neanderthals were not the dimwits of popular imagination. It is possibly the strongest indication yet that they were capable of symbolic behaviour

References:
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1.            Rodr√≠guez-Vidal, J. et al., A rock engraving made by Neanderthals in Gibraltar. PNAS (Early edition) (2014).

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Tuesday, 2 September 2014

Neolithic boom-to-bust

Transition to agriculture triggered demographic growth followed by collapse

Researchers have used two sets of data from the period 6000 to 2000 BC to investigate the demographics of the transition to agriculture in Europe: data from cemeteries, and radiocarbon dates from 24 well-documented archaeological regions across Europe.

The juvenility index is the proportion of a population aged between 5 and 19 years old: in an increasing population, this is high; in a declining population it is low. Researchers obtained data from 212 cemeteries, weighting results by settlement size. They then considered the Summed Calibrated Radiocarbon Date Probability Distribution (SCDPD) of 8,032 radiocarbon dates, which can be used as a proxy for population density and indicate whether populations are rising or falling at a given time.

Both sets of data gave similar results. The transition from Mesolithic to Neolithic in each region was accompanied by a sharp increase in the population, but after a period of stability there was a decline. The cemetery data indicated a period of growth lasting for about 720 years, a period of stability lasting for just under 1,000 years, followed by a decline. The use of radiocarbon dates is less proven as a proxy, but because far more data is available it should provide higher resolution results. The radiocarbon dates indicated that the period of growth had lasted for 420 years before a decline set in, lasting for 840 years for a complete boom to bust cycle of 1,260 years. That the two sets of results are reasonably consistent confirms SCDPD as a valid demographic proxy.

References:
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1.            Downey, S., Bocaege, E., Kerig, T., Edinborough, K. & Shennan, S., Correlation with Juvenility Index Supports Interpretation of the Summed Calibrated Radiocarbon Date Probability Distribution (SCDPD) as a Valid Demographic Proxy. PLoS One 9 (8), e105730 (2014).
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