New dates and palaeoenvironmental evidence for the Middle to Upper Palaeolithic occupation of Higueral de Valleja Cave, southern Spain

Abstract

A research programme has been set up at Higueral de Valleja Cave in southern Spain to investigate the late survival and eventual extinction of the southern Iberian Neanderthals and the arrival of modern humans. Of key interest in the first phase of research was to understand the depositional environment in the entrance chamber of the cave and to establish whether palaeoenvironmental and dating samples could be retrieved from the Middle and Upper Palaeolithic sequences. The outcome is a series of OSL, TL and radiocarbon dates showing that the cave was occupied by Neanderthal populations in Marine Isotope Stage (MIS) 3, if not earlier, and by modern human Solutrean populations during the last glacial maximum. Cave sediments provisionally indicate that the lower Middle Palaeolithic sequence (X–VIII) formed in warm and humid environments and the upper sequence (VIII–V) formed when the climate was cooler and drier. The presence of long grass phytoliths and of the small mammals Microtus duodecimcostatus, Microtus brecciensis and Apodemus sylvaticus in the upper sequence indicates that a range of habitat types persisted near the cave including grassland, scrubby vegetation, patchy tree cover and ponds. This raises the possibility that environmental factors were key factors in the late survival of Neanderthal populations at the cave.

Introduction

The fate of the Neanderthals is a topic of considerable interest in human evolutionary research. Perhaps the most widely accepted explanation for their disappearance is that they were replaced by incoming modern human populations, who with a marginally greater intelligence and superior tool-kit were able to displace the Neanderthals from their preferred habitats (Mellars, 2006). In recent years, the role of climate change has increased in significance as a primary causal factor with the observation in marine and ice cores of rapid climate oscillations during Marine Isotope Stage (MIS) 3 (c.59 000–24 000 BP). Stringer et al. (2003) demonstrated that climate conditions were most stressful for Neanderthal populations between 40 000 and 30 000 BP, which is the time when they are commonly thought to have disappeared. A contribution is made to this topic here with the presentation of the results of a programme of environmental sampling at Higueral de Valleja Cave in the south of the Iberian Peninsula. The cave is of particular interest because it is less than 80 km north of Gorham's Cave in Gibraltar (Fig. 1), where claims have recently been made for a very late persistence of the Middle Palaeolithic possibly even as young as 24 000 BP (Finlayson et al., 2006).

Reasons for the late survival of Neanderthal populations in southern Iberia are currently under debate. Those who consider modern humans as primarily responsible for their extinction believe it is explained by geography and historical contingency: the region is the most southerly in Europe and was furthest from the initial expansion of modern human population into the continent, which took place as early as 46 000 years ago via the Levant (Mellars, 2006). However, while modern humans were in the north of Iberia by 41 000 BP, the earliest Upper Palaeolithic evidence in the south dates to ca. 35 000 uncal BP (Bajondillo Cave, Málaga, see Cortés Sánchez, 2003). Zilhão (2000) proposed that a biogeographical boundary – the Ebro Frontier – prevented the earlier arrival of modern humans in the south and west of Iberia. The boundary ran along the Ebro River in Cataluña and across the Iberian Peninsula. He regarded land to the south of the Ebro Frontier to have been too heavily forested during MIS 3 to allow a rapid southerly expansion by modern humans. A problem with this idea is that modern humans probably reached southern Iberia by following the coast, thus circumventing the hypothesised biogeographical frontier.

Finlayson (1999) attributed the late survival of the southern Iberian Neanderthals to the continued existence of their habitats in the region during MIS 3. Southern Iberia was an attractive occupation area at this time: its varied terrain meant a high number of environmental gradients would have been present; it was within the Mediterranean temperature biome; precipitation would have been high on the western windward side of the Betic Mountain System, the main mountains of southern Iberia; river networks were far reaching; and the coastline was extensive. All of these factors contributed to the biodiversity of the region during the last glacial. For Finlayson, the availability of a range of habitats was key to the success of the southern Iberian Neanderthals: it was this success that postponed the arrival of modern humans in the region. He also regarded modern humans as a species that favoured open plain environments, few of which existed in southern Iberia during the last glacial. His theories are supported by the results of Hewitt (2000), who used genetic evidence to show that southern Iberia functioned as a refuge for a range of plant and animal species at this time.

Nevertheless, the southern Iberian Neanderthals eventually disappeared. Finlayson (1999) proposed that millennial scale climate oscillations of late MIS 3 led to the eventual fragmentation of Neanderthal habitats and ultimately to population decline beyond the point of recovery. In his view, the arrival of modern humans was incidental to their extinction. d'Errico and Sánchez Goñi (2003) disagreed and stated that Heinrich Event 4, a major episode of ice raft deposition in the Atlantic Ocean ca 40 000 years ago, led to a modern human range expansion into the Iberian Peninsula and an eventual contact with the Neanderthal populations of southern Iberia. Both views are in need of substantiation with archaeological and environmental evidence. The latter drew upon pollen evidence from marine cores recovered in the Alborán Sea off the coast of southern Iberia to support their position, but the reliability of applying such data for environmental reconstruction was called into question by Finlayson et al. (2004) and Carrión (2004).

Higueral de Valleja was selected for environmental sampling because it is known to contain Middle and Upper Palaeolithic archaeological evidence (Giles Pacheco et al., 1998). In conjunction with a lithostratigraphic analysis of the cave sediments and the first radiometric dates to come from the site, the results offer new insights into the Neanderthal and modern human occupation of the region during MIS 3 and MIS 2.