The role of the southern Caucasus on early human evolution and expansion—refuge, hub or source area?

The role of the southern Caucasus on early human evolution and expansion—refuge, hub or source area?

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Transcript The role of the southern Caucasus on early human evolution and expansion—refuge, hub or source area? Angela A. Bruch, Andrew W. Kandel & David Lordkipanidze Introduction Figure 1.  Geographical setting of the study areas mentioned in the text. Click to enlarge . With 1.8-million-year-old evidence of human presence documented at the fossil site of Dmanisi in the Republic of Georgia, the southern Caucasus represents a key region for studying early human evolution and expansion out of Africa and onto the Eurasian continent. The area also  provides a long record of human occupation throughout the Palaeolithic. The pace and causes of human colonisations during the Early Pleistocene, however, remain a matter of debate: for example, whether in one or several migratory waves from Africa into new Eurasian environments, as well as the later expansions of Neanderthals and anatomically modern humans. Climate change is considered to be a major factor driving hominin evolution and dispersal,  because climate modulates the availability of resources directly or indirectly through its influence on vegetation, landscape physiography and animal distribution. To understand the influence of environmental factors on early humans, an international workshop was convened at the National Museum of Georgia in Tbilisi, 15–20 October 2013. The aim of the meeting was to exchange and discuss the latest scientific results from the southern Caucasus (Figure 1) with regard to early human evolution, range expansions and technological developments against the backdrop of environmental change over the last two million years. More than 40 researchers from varied scientific fields presented their research in 23 oral and 18  poster contributions held over three sessions. In this short contribution, we review some of the key evidence presented and discussed. Dmanisi: the first 'Out of Africa'—what do we know and what do we want to know? The fossil hominin site of Dmanisi (Figures 2 & 3) has produced a growing collection of over 60 cranial and post-cranial human remains including at least five individuals ranging in age from  juvenile to older adult; most recently Lordkipanidze et al  . (2013) have presented a completely  preserved Early Pleistocene adult cranium from Dmanisi. These morphologically diverse remains of early  Homo  show affinities with African fossils and suggest that we should expect intraspecific variability in early hominins. This discovery has ramifications not only for a more streamlined classification of the early hominin lineage, but also for continuity of species across continents. Taphonomic studies of the mammalian fauna, as well as analyses of lithic artefacts and tool use, shed further light on these first inhabitants of Dmanisi. The results demonstrate how the Dmanisi hominins contradict earlier assumptions about how the first migrants out of Africa should appear. In fact, they were physically small, had small brains and made use of stone tools. On the one hand, stone tools may have been necessary for protection (animal dens attest to the contemporaneous use of the site by both hominins and carnivores, implying a high chance of confrontation; Bruch & Lordkipanidze 2013: 29). On the other hand, evidence for modification of the fauna through cut marks, hammer-stone marks and notches is much rarer than carnivore modification and supports the interpretation that hominins had early access to carcasses. Whether hunted or power scavenged, the fauna were also exploited for their marrow and skins (Bruch & Lordkipanidze 2013: 55–56). Nonetheless, plant resources probably played a considerable role compared to meat consumption (Bruch & Lordkipanidze 2013: 45). Figure 2.  Overview of the Dmanisi fossil site with excavation area in the foreground. Click to enlarge . Figure 3.  Reid Ferring led the tour of Dmanisi. Click to enlarge . Palaeoenvironmental studies based on Dmanisi's small mammalian fossils suggest an open, steppe environment, with the presence of wooded areas in the vicinity. Climatic conditions inferred from palaeoherpetological data confirm an environment more arid than present, especially during summer. This would support the development of more open landscapes than are present today (Bruch & Lordkipanidze 2013: 19). Since the palaeoenvironmental context of the Dmanisi hominins cannot be clarified using on-site proxies alone (e.g. Messager et al  . 2010), attention has turned to a wider spatial frame. Early Pleistocene environmental changes in the southern Caucasus Recent work on reconstruction of the climate and vegetation in Georgia and Armenia during the time of early human expansion into Eurasia has focused on three study areas in the southern Caucasus with the aim of achieving a regional correlation of the environmental setting in time and space. Figure 4.  Diatomite sections in the Vorotan Basin, southern Armenian highlands. Figures 4–6 show the high variability of landscapes in the southern Caucasus (photograph: A. Gonschior). Click to enlarge . In the Vorotan Basin of southern Armenia (Figure 4), lake sediments provide detailed information on environmental changes during the late Early Pleistocene within a well constrained stratigraphic context. Results based on pollen, macroflora and insect fossils document a clear vegetation response to orbitally forced global climatic changes. Open vegetation was present during the less pronounced climatic cycles, and broad-leaved deciduous forests expanded during very warm and humid phases. Based on the precise age control gained in the Vorotan Basin, the results serve as a reference for correlation with the other two regions where investigations have only recently begun. In western Georgia (Figure 5), the stratigraphic correlation and age determination will serve as a foundation for the ongoing analyses of vegetation and climate history of the Pleistocene (Bruch & Lordkipanidze 2013: 41). Palaeoenvironmental information from a third study area in southern Georgia (Figure 6) is based mainly on the large mammalian fauna of Akhalkalaki. A quantitative ecological analysis using the eco-profiles of large herbivores shows the future potential of this method (Bruch & Lordkipanidze 2013: 35). Its positive correlation with the first palynological data from the area, as well as with the spectrum of large mammalian fauna from Dmanisi, shows promise (Bruch & Lordkipanidze 2013: 43). Figure 5.  Warm-temperate broad-leaved forests of the western Georgian lowlands. Click to enlarge . Figure 6.  Javakhetian highlands, southern Georgia, near Akhalkalaki. Click to enlarge . Based on these results, it will be possible to extrapolate the distribution of forests and mosaic landscapes in the southern Caucasus for the different climatic phases of the Early Pleistocene in more detail. Especially pronounced warm phases like MIS 31 caused a remarkable expansion of mosaic landscapes, offering a great variety of habitats with increased availability and diversity of  plant and animal resources. Those environmental settings might have been particularly favourable for human occupation, expansion and cultural development. The southern Caucasus Palaeolithic: occurrence or co-occurrence of Neanderthals and the first anatomically modern humans? The southern Caucasus also provides insight into the Middle and Upper Palaeolithic periods and, in particular, the timing and reconstruction of the palaeoenvironmental habitats in which
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