Genomic Data Reveal a Complex Making of Humans Oct 22, 2013 21:08:34 GMT
Post by Admin on Oct 22, 2013 21:08:34 GMT
A record of Neanderthal history, thought to be lost a century ago, has been re-discovered in Jersey. The island is believed to be one of the last places the Neanderthals lived after teeth were discovered on its Cotte de St Brelade cave (pictured) in 1910
Modern humans were living in Italy and the UK as far back as 41,000-45,000 years ago, putting them in contact with European Neanderthals who persisted on the continent for many millennia after these dates. On the Rock of Gibraltar, Neanderthals could possibly have survived around until as recently as 28,000 years ago before finally dying out. Neanderthals also lived on the Channel Island of Jersey from around 250,000 years ago until between 100,000 and 47,000 years ago and the sequence of sediments at the site of La Cotte de St Brelade dates between 100,000 and 47,000 years old, indicating that Neanderthal teeth which were discovered at the site in 1910 were younger than previously thought.
In 2011, a programme of field research was undertaken to effect the stabilization of an unstable section in the West Ravine at the key Neanderthal occupation site of La Cotte de St Brelade on the Channel Island of Jersey. As part of this essential remedial work the threatened section was analysed to characterize its archaeological and palaeoenvironmental potential as well provide optically stimulated luminescence (OSL) dates. The work determined, through two concordant OSL dating programmes, that the section formed part of an extensive sequence of sedimentation spanning >105 to <48 ka. Furthermore, reanalysis of the archive determined that the sediment sequence examined contained the stratigraphic equivalent of deposits lying below those that have previously produced Neanderthal fossils. Through our work, we can now constrain these younger sediments to being younger than 48 ka. The combined results suggest that this sequence now represents the recovery of an extensive dataset, thought lost to science through complete excavation, which holds the potential to throw light on the disappearance of Neanderthal populations from the Atlantic-edge outpost on the north-west frontier of their world.
The evidence for Neanderthal lithic technology is reviewed and summarized for four caves on The Rock of Gibraltar: Vanguard, Beefsteak, Ibex and Gorham’s. Some of the observed patterns in technology are statistically tested including raw material selection, platform preparation, and the use of formal and expedient technological schemas. The main parameters of technological variation are examined through detailed analysis of the Gibraltar cores and comparison with samples from the classic Mousterian sites of Le Moustier and Tabun C. The Gibraltar Mousterian, including the youngest assemblage from Layer IV of Gorham’s Cave, spans the typical Middle Palaeolithic range of variation from radial Levallois to unidirectional and multi-platform flaking schemas, with characteristic emphasis on the former. A diachronic pattern of change in the Gorham’s Cave sequence is documented, with the younger assemblages utilising more localized raw material and less formal flaking procedures. We attribute this change to a reduction in residential mobility as the climate deteriorated during Marine Isotope Stage 3 and the Neanderthal population contracted into a refugium.
Figure 1. The location of sites mentioned in the text.
Inset: the location of Gibraltar on the Iberian Peninsula.
The Rock of Gibraltar is a limestone klippe peninsula at the southern tip of Iberia (Figure 1) and represents the south-western extremity of the Neanderthal range. Both wave and solutional erosion have created a series of caves in the klippe, particularly on its more exposed eastern side, which were inhabited by Neanderthals and then Homo sapiens over the last 100 thousand years. Gibraltar is home to some of the world’s most significant Neanderthal sites. The region is historically significant as one of the first discoveries of Neanderthal skeletal remains was made in Forbes Quarry in 1848 , . Important dietary information has been obtained from the Gibraltar caves, including the exploitation of a range of terrestrial and marine species unparalleled at other Neanderthals sites , . Gibraltar also boasts having the youngest Mousterian sites in Europe, suggesting that the area served as a refugium for the final Neanderthals , .
Bio-climatic modelling indicates that the favoured habitats of the southern Iberian Neanderthals became fragmented during MIS3 separating coastal and upland populations , with much of the interior of Iberia becoming arid . The MIS3 occupation of Gorham’s Cave may represent a Neanderthal population which foraged locally along the coast and did not exploit inland resources to the same extent as their predecessors had done. Indeed, the low seas level stands of MIS3 would have opened up new shore habitats immediately in front of Gibraltar , . This may explain why the technology becomes increasingly expedient and made on more local materials during the later occupation phases at Gorham’s, reflecting reduced residential mobility and greater emphasis on foraging on and around The Rock. Waechter’s layer G has a far higher artefact density than the underlying layers, suggesting more intensive occupation, perhaps as a result of a reduced residential mobility pattern . An increase in the quantity of charred material in the MIS3 occupation of Gorham’s also indicates more intensive hominin occupation at this time .
Parallels may be found with MIS3 Neanderthals populations elsewhere. In the southern Caucasus the environment was stable and diverse, like Gibraltar, and also did not suffer the MIS3 deterioration to the same extent as surrounding regions . In the late Middle Palaeolithic of the southern Caucasus, prior to replacement by Homo sapiens c. 37kya, there was also a reduction in Neanderthal range size with far fewer exotic materials being exploited than in the earlier Middle Palaeolithic . In the Middle Palaeolithic of Latium, Italy, the onset of MIS3 coincided with a reduction in the import of exotic materials and a shift away from radially prepared cores for striking larger flakes, to bidirectional small flake cores .
Gibraltar has been hypothesized to be one of the last refuges of the Neanderthals with a date of 28 kya for the youngest Mousterian occupation in Layer IV of Gorham’s Cave  . This young age has been challenged partly on technological grounds with the suggestion that the Layer IV occupation of Gorham’s actually represents the early Upper Palaeolithic rather than the latest Mousterian . However, there are no blade cores, or even blade scars on the cores from Layer IV. There is also continuity between Layer IV and the older members of Gorham’s Cave in the use of large rounded quartzite cobbles as single platform cores and in the production of small discoidal cores on chert. In accordance with previous analyses  we must therefore assign the Layer IV artefacts to the Mousterian. The absence of any Levallois cores from this final occupation could reflect a dwindling population in which the expertise required for this most complex of Middle Palaeolithic technologies has been lost (sensu Henrich, ), but larger samples are needed to test this hypothesis.
The Mousterian record from the Gibraltar caves provides a rich sequence of Neanderthal occupation in an optimal habitat. The high biodiversity and stability of the Gibraltar climate may have allowed this region to act as a refugium for the last surviving Neanderthals , , . As the climate deteriorated during MIS3 the technological response of the Neanderthals was to use more expedient flaking strategies on locally available material, reflecting a reduction in mobility and a contraction into the core zone of the refugium.