Geoffrey N. Bailey

Landscapes of human evolution: models and methods of tectonic geomorphology and the reconstruction of hominin landscapes

This paper examines the relationship between complex and tectonically active landscapes and patterns of human evolution. We show how active tectonics can produce dynamic landscapes with geomorphological and topographic features that may be critical to long-term patterns of hominin land use, but which are not typically addressed in landscape reconstructions based on existing geological and paleoenvironmental principles. We describe methods of representing topography at a range of scales using measures of roughness based on digital elevation data, and combine the resulting maps with satellite imagery and ground observations to reconstruct features of the wider landscape as they existed at the time of hominin occupation and activity. We apply these methods to sites in South Africa, where relatively stable topography facilitates reconstruction. We demonstrate the presence of previously unrecognized tectonic effects and their implications for the interpretation of hominin habitats and land use. In parts of the East African Rift, reconstruction is more difficult because of dramatic changes since the time of hominin occupation, while fossils are often found in places where activity has now almost ceased. However, we show that original, dynamic landscape features can be assessed by analogy with parts of the Rift that are currently active and indicate how this approach can complement other sources of information to add new insights and pose new questions for future investigation of hominin land use and habitats.

Active tectonics and human survival strategies

Tectonic movements continuously remould the surface of Earth in response to plate motion. Yet such deformation is rarely taken into account when assessing landscape change and its impact on human land use, except perhaps as an occasional hazard to human life or a temporary disruption in the longer term patterns of human history. However, active tectonics also create and sustain landscapes that can be beneficial to human survival, forming a complex topography of potentially fertile sedimentary basins enclosed by mountain barriers that can facilitate the control and exploitation of food resources, especially animal prey. We discuss the tectonic history of northwest Greece and show how the Paleolithic sites of the region are located to take advantage of tectonically created features at both a local and a regional scale. We suggest that the association of significant concentrations of early Paleolithic sites with tectonically active regions is not coincidental and that on the longer time spans of human biological evolution, active tectonics has been an important selective agent contributing to the development of the human species as an intelligent predator.

Evolution and dispersal of the genus Homo: A landscape approach.

The notion of the physical landscape as an arena of ecological interaction and human evolution is a powerful one, but its implementation at larger geographical and temporal scales is hampered by the challenges of reconstructing physical landscape settings in the geologically active regions where the earliest evidence is concentrated. We argue that the inherently dynamic nature of these unstable landscapes has made them important agents of biological change, creating complex topographies capable of selecting for, stimulating, obstructing or accelerating the latent and emerging properties of the human evolutionary trajectory. We use this approach, drawing on the concepts and methods of active tectonics, to develop a new perspective on the origins and dispersal of the Homo genus. We show how complex topography provides an easy evolutionary pathway to full terrestrialisation in the African context, and would have further equipped members of the genus Homo with a suite of adaptive characteristics that facilitated wide-ranging dispersal across ecological and climatic boundaries into Europe and Asia by following pathways of complex topography. We compare this hypothesis with alternative explanations for hominin dispersal, and evaluate it by mapping the distribution of topographic features at varying scales, and comparing the distribution of early Homo sites with the resulting maps and with other environmental variables.

Marine Radiocarbon Reservoir Effect in Late Pleistocene and Early Holocene Coastal Waters off Northern Iberia

Radiocarbon dating of closely associated marine mollusk shells and terrestrial material (mammal bones or charred wood) collected from archaeological contexts in northern Atlantic Iberian coastal areas is used to quantify the marine 14C reservoir effect (ΔR) for the coastal waters off the Cantabrian coast (northern Iberia). For the first time, ΔR values were reliably determined for these coastal waters, and also for the first time a ΔR was calculated for the Late Pleistocene in Atlantic Iberia. Pairs of coeval samples of different carbon reservoirs selected from Upper Paleolithic (Late Pleistocene) and Mesolithic (Early Holocene) contexts yielded ΔR weighted mean values of −117±70 14C yr and −105±21 14C yr, respectively. These values show oceanographic conditions characterized by a reduced offset between atmospheric and surface water 14C contents, suggesting a nonexistent or a very weak upwelling and some stratification of the water column. Similar oceanographic conditions have been recorded in other areas of Atlantic Iberia during the Holocene, such as off Andalusian and northwestern Galician coasts. Results not only provide useful information on environmental conditions but also a framework to obtain more precise and reliable absolute chronologies for the Late Pleistocene and Early Holocene in northern Iberia.

Mapping, modelling and predicting prehistoric coastal archaeology in the southern Red Sea using new applications of digital-imaging techniques

Abstract Over 3,000 shell-midden sites have been located in the southern Red Sea using digital-imaging techniques, in a combination of palaeo-landscape reconstruction and remote survey. The primary methods include digital-imaging techniques – high-resolution satellite images, false colour images and radar data. Surveying and recording these sites during excavation has also been enhanced using digital photogrammetry – allowing high-resolution site-level data to be incorporated into wider landscape reconstructions. The resulting data are combined to construct site location models that have been proved and tested in other areas of the southern Red Sea. We also show how satellite imagery can be modified and exploited for seabed mapping and the search for underwater sites.

New Developments in Submerged Prehistoric Archaeology: An Overview

Research on the archaeology of the continental shelf has made slow and intermittent progress over the past 40 years amidst an ongoing mood of scepticism in the wider scientific and archaeological community, but with a marked acceleration of interest and investment of new resources during the past decade. The chapters in this volume demonstrate that relevant evidence is now being retrieved and systematically examined across the world in all the major continents and in deeper as well as shallower water, and that new ideas and new data are now providing the momentum for future development. This chapter draws on examples from the other chapters in the volume to reflect on the history of developments in this field and the shifts in the climate of opinion that have led to increasing acceptance of its importance; the research questions that are now coming more clearly into focus and the directions they suggest for the future; and the challenges of developing purposeful strategies of exploration and discovery of new material.

Geology and archaeology: submerged landscapes of the continental shelf: an introduction

Sea-level change has influenced human populations globally since prehistoric times. Even in early phases of cultural development, human populations were faced with marine regression and transgression associated with the glacial–interglacial climatic cycle, amplified by glacio-isostatic adjustments in some regions. Global marine regression during the last glaciation changed the palaeogeography of the continental shelf, converting former marine environments to attractive terrestrial habitats for prehistoric human occupation, and adding an extensive new increment of land, in the case of Europe amounting to an additional 40% of the existing land area, and on a global scale to some 20 million km of additional territory that is now submerged. These areas of the shelf were used as hunting and gathering areas, and as pathways of dispersal between regions and between continents, until they were resubmerged by the post-glacial marine transgression. They also most probably witnessed the earliest developments in seafaring, marine exploitation and permanent settlements. Based on modern marine research technologies and the integration of large databases, proxy data are now becoming available for the reconstruction of these submerged Quaternary landscapes. Concerted efforts are also now being devoted to the search for prehistoric archaeological sites and artefacts on the seabed, often in collaboration with marine scientists. This search has been stimulated by the increasing amount of material that has demonstrably survived inundation, often with excellent preservation of organic remains, by closer collaboration with offshore industry, and by the growing realization of the importance of these submerged data for understanding human prehistoric developments during periods of rapidly changing climate and environment. Moreover, these new research trends are not simply being driven by an archaeological need for scientific and technological input from other disciplines, but by collaborations involving genuine mutual benefit, in which all partners have something to gain. Archaeological problems often pose new questions about geological change, stimulating new techniques of observation, new technologies and new investigations, which in their turn can offer new data, often at higher resolution and with better dates, in relation to geological and environmental issues such as sea-level change and palaeoclimatic variability on the continental shelf. The expansion of early human populations to occupy new territory and new continents is one of the great narratives of human evolution. It is currently a theme of wide interest and topicality, and has received significant impetus and publicity from the new science of palaeogenetics. Together with ongoing discoveries of new fossil and archaeological material, and new studies of palaeoclimate and palaeoenvironment, the field itself is rapidly expanding, leading to new discoveries and new controversies (Grine et al. 2009; Gamble 2013; Smith & Ahern 2013). All the current indications are that the human species originated in Africa, with at least two major episodes of dispersal. The earliest, some time after about 2 myr ago, led to the expansion of Homo ergaster/erectus populations across southern Europe and Asia, extending from Britain in the west to China and Indonesia in the east and south. The second involved our own species, Homo sapiens (Anatomically Modern Humans or AMH), and took place some time after about 200 ka. This resulted in the replacement of earlier hominin populations in Europe and Asia, and expansion further afield: into New Guinea and Australia, certainly involving sea crossings over distances of at least 50 km, by about 50 ka; to the higher latitudes of northern Eurasia, with entry into the Americas by at least 15 ka; and into new territory exposed by the melting of the northern hemisphere ice sheets less than 10 kyr ago. Anthropological and archaeological investigations of these processes are directly connected

Human bipedalism and the importance of terrestriality

The paper by Thorpe et al. (above) follows on from our own paper (Winder et al. 2013); in setting out their view that bipedalism has arboreal origins, they present a critique of our hypothesis, which we address below. We begin by observing that their views and ours are not in contradiction. We criticised ‘forest hypotheses’ of human evolution, not because we think they are wrong but because we think they are incomplete. In fact we agree with Thorpe et al. about the arboreal origin of bipedalism amongst certain groups of apes. What we are interested in, and what they do not address, is a different set of issues: how and why some apes, already perhaps pre-adapted to bipedalism in their anatomy, became committed to a terrestrial (non-arboreal) pattern of existence. We do not argue that upright posture cannot be explained by arboreal selective pressures, rather that such an explanation is not ipso facto sufficient to explain all hominin adaptations or produce all the features needed to survive on the ground. We reject their view that our model suggests “a single newly identified driver; adaptation for ‘complex topographies’” (Thorpe et al. above, p. 911; emphasis in the original). We wrote about ecologically and structurally complex landscapes, and used ‘complex’ or ‘rough’ topography as a proxy. Rough terrain is one of several characteristics all complex landscapes might be expected to share and which can be identified (at least to a degree) in the palaeoenvironmental record. We do not suggest that all terrestrial landscapes with rough terrain exert a uniform selective regime on their inhabitants—let alone a single selective pressure—not least because rough landscapes vary considerably in their vegetation cover. We also clearly stated that our model requires no assumptions about the anatomy or behaviour of the last common ancestor. It is thus not in any way incompatible with an arboreal, bipedal ancestry. On the contrary, it adds another layer to such a model, providing a ‘missing link’ between existing theories that work well for the earliest and latest periods of hominin evolution but not for the transition between them. Thorpe et al. also criticise our hypothesis for not explaining why different characteristics of terrestrial bipedalism appeared piecemeal in the fossil record. However, it is a misconception to suppose that we proposed a single, simple selective pressure, which must necessarily act at a specific time in our evolutionary history. In fact, our model specifies a multi-stage trajectory, involving adaptation to complex landscapes as a first stage, and expansion beyond them through tactical use of terrain in a later stage. Central to our hypothesis is the importance of

Migration: Value of submerged early human sites

Your articles on human dispersal in the late Pleistocene epoch (Nature 485, 23; 2012) overlook the significance of now-submerged archaeological sites on the continental shelf during this period (126,000–11,000 years ago). It is wrong to assume that these were completely destroyed by the sea and that the interpretation of human movements must rely on proxy data, such as DNA or evidence from islands. More than 3,000 prehistoric sites on the seabed have been found and mapped, and in some cases excavated. They range in age from 500,000 to 5,000 years old, and at locations from the present-day shoreline out to a depth of 130 metres. These sites were extensive, often located on key travel routes and more attractive than arid hinterlands to human settlers. Marine archaeologists have recovered in-context stone artefacts, animal remains and human fossils from such sites. Some materials, including food remains, organics, bone, DNA and plants, are better preserved underwater than on land. Questions of early human dispersal will not be resolved until continental shelves are fully investigated — spurred by advances in modern oceanographic technology (see http://splashcos.org).

Submerged landscapes of the European continental shelf: Quaternary paleoenvironments

Quaternary Paleoenvironments examines the drowned landscapes exposed as extensive and attractive territory for prehistoric human settlement during the Ice Ages of the Pleistocene, when sea levels dropped to 120m-135m below their current levels. This volume provides an overview of the geological, geomorphological, climatic and sea-level history of the European continental shelf as a whole, as well as a series of detailed regional reviews for each of the major sea basins. The nature and variable attractions of the landscapes and resources available for human exploitation are examined, as are the conditions under which archaeological sites and landscape features are likely to have been preserved, destroyed or buried by sediment during sea-level rise. The authors also discuss the extent to which we can predict where to look for drowned landscapes with the greatest chance of success, with frequent reference to examples of preserved prehistoric sites in different submerged environments.