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Tectonics, Volcanism, Landscape Structure and Human Evolution in the African Rift This is a repository copy of Tectonics, volcanism, landscape structure and human evolution in the African Rift. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/1169/ Book Section: Bailey, G. orcid.org/0000-0003-2656-830X, Manighetti, I. and King, G. (2000) Tectonics, volcanism, landscape structure and human evolution in the African Rift. In: Bailey, G., Charles, R. and Winder, N., (eds.) Human Ecodynamics. Symposia of the Association for Environmental Archaeology . Oxbow Books , pp. 31-46. Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ 5. Tectonics, Volcanism, Landscape Structure and Human Evolution in the African Rift Geoff Bailey, Geoffrey King and Isabelle Manighetti Tectonic movements and volcanism in the African Rift have usually been considered of relevance to human evolution only at very large geographical and chronological scales, principally in relation to long- term topographic and climatic variation at the continental scale. At the more loco1 scale of catchment basins and individual sites, tectonicfeatures are generally considered to be at worst disruptive and at best incidental features enhancing the preservation and exposure of early sites. We demonstrate that recent lava flows and fault scarps in a tectonically active region create a distinctive landscape structure with a complex and highly differentiated topography of enclosures, barriers and fertile basins. This landscape structure has an important potential impact on the CO-evolution of prey-predator interactions and on interspecific relationships more generally. In particular, we suggest that it would have oflered unique opportunities for the development of a hominid niche characterised by bipedalism, meat-eating and stone tool use. These landscape features are best appreciated by looking at areas which today have rapid rates of tectonic movement and frequent volcanic activity, as in eastern Afar and Djibouti. These provide a better analogy fur the Plio-Pleistocene environments occupied by early hominids than the present-day landscapes where their fossil remains and artefacts have been discovered. The latter areas are now less active than was the case when the sites were fumed. lley have also been radically transfomed by ongoing geomorphological processes in the intervening millennia. Thus, previous attempts to reconstruct the local landscape setting adjacent to these early howinid sites necessarily rely on limited geological windows into the ancient land surface and thus tend tofilter out small-scale topographic detail because it cannot be reliably identwed. It is precisely this local detail that we consider to be of importance in understanding the environmental contribution to CO-evolutionaryde~e~o~~en~s. Keywords: NORMALFAULTING; LAVA FLOWS; AFAR; AFRICAN RIFT; HOMINIDS. INTRODUCTION 1993: Manighetti et al. 1997, 1998). These studies have, Our aim in this paper is to bring together two bodies of however, been largeIy pursued without reference to their knowledge that have, for the most part, been pursued in potential impact on the course of human development. isolation from each other. On the one hand is the On the other hand the palaeoanthropological and geological investigation of the dynamics of rift formation archaeological investigation of human evolution has using the new techniques of tectonic geomorphology. focused on such issues as changes in the biological and Considerable advances have been made during the past cultural potential of early horninids, their intra-specific decade in our understanding of African tectonics both in social interactions, and their inter-specific ecological terms of large-scale dynamics and, of particular relevance interactions with prey and predator organisms. Discussion to this paper, their influence on local and regional changes ofthe physical environment in relation to early hominids of the physical environment (Stein et al. 1991;Manighetti has mainly emphasised large-scale changes of climate, 32 GeofS Bailey, GeofSrey K ring and Isabelle Manighetti vegetation and tectonics, and interactions between them the interaction between hominids and tectonically active (e.g. Foley 1994, in press; Partridge et al. 1995a; Vrba environments resulted in new configurations of hominid 1996; Vrba et al. 1995), or small-scale reconstructions behaviour that wouId not otherwise have occuhed. Early of sedimentary environments, food and raw materials hominids selected certain sorts of environments, and these available within the vicinity of archaeological sites (e.g. in turn selected for certain sorts of hominFd behaviours Blumenschine & Peters 1998; Brown & Feibel 1991; in a process of reciprocal interaction that amplified some Harris & Herbich 1978; Rapp & Vondra I98 1). Tectonic patterns of behaviour at the expense o& others. This factors have in general played very little role in interpre- process is simiIar in some respects to that of a co- tation except in indirect terms: as an ultimate cause of evolutionary relationship, commonly defined in biology global climatic change (Ruddiman & Raymo 1988); as as a situation in which two or more taxa undergo an indirect forcing agent on mammalian evolution through evolutionary change as a result of reciprocal selective the impact on regional climatic variation (Partridge et pressures that each imposes on the other through their al. 1995b); as a source of ecological diversity (Coppens mutual ecoIogica1 interaction (Pianka 1980). Recent 1994; Foky 1987: Gamble 1993); or simply as a examples of land use, where human activity is having a mechanism for accelerating the protection and discovery dramatic impact on the physical landscape and the of finds by rapid sedimentation and subsequent exposure changed physical landscape in its turn is further affecting by erosion. human activity, could properly, in our view, be described Thus, the landscapes studied by geomorphologists, as an example of a CO-evolutionaryprocess invoIving geologists and geophysicists are typically dominated by reciprocal interactions between physical, biological and physical dynamics, and the human occupants are essen- cultural variables. The example that we describe below tially out of sight or at best passive spectators. Conversely, is not strictly a case of CO-evolutionarydevelopment in an archaeological or palaeoanthropological perspective that sense because the physical landscape was not (so is one dominated by a foreground of biological and cultural far as we know) affected by the presence of hominid or dynamics with hominids as the centre of focus and an other large-mammal activity. On the other hand, the essentially passive and distant, albeit variable and distinctive landscapes that we describe below could have changing, physical environment. The artist's recon- significantly altered or accelerated the pattern of co- struction of an early hominid scene (Fig. 5.1) offers a evolutionary relationships between biological species, graphic if somewhat exaggerated ilIustration of this point, and cannot be treated as an essentially passive or uniform with a foreground of active and indeed violent socid tabula rasa awaiting the imprint of ecologicaI and interactions, and an environmental background composed, evolutionary processes. We suggest that concepts of co- appropfiately enough, of a volcanic mountain largely evolutionary behaviour and environmental selection obscured by cloud. provide a fruitful framework for examining interactions Here we focus on the dynamic interactions that occur between variations of the physical environment and its at the interface between the physical environment and biotic occupants including humans, and one that avoids hliman behaviour at the local scale. In particular we aim the charge of determinism and the consequent dismissal to show that the tectonics of the African Rift create a of relevant factors - environmental, behavioural or distinctive and complex topographic structure character- cultural as the case may be. ised by varying combinations of changing lake basins and river vaIleys, fauIt scarps and lava flows. We argue that a landscape structured in this way was highly attractive to early hominids, and may have exerted TECTONIC ENVIRONMENTS AND PALAEOLITHIC SUBSISTENCE selective pressures favouring bipedalism, the exploitation of animaI foods, and evolutionary divergence. We begin with a brief example from the Middle and Discussion of interactions between humans and the Upper Palaeolithic of north-west Greece, an area which physical environment tends to veer towards one of two is subject to very high rates of tectonic activity as a extremes. Either humans are seen as passive tools of consequence of its position at the boundary between the environmental change, or the environment is treated as African and European plates (BaiIey et al. 1993; King et essentially inert until acted on by
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