Geoff Bailey

Rethinking the dispersal of Homo sapiens out of Africa.

Current fossil, genetic, and archeological data indicate that Homo sapiens originated in Africa in the late Middle Pleistocene. By the end of the Late Pleistocene, our species was distributed across every continent except Antarctica, setting the foundations for the subsequent demographic and cultural changes of the Holocene. The intervening processes remain intensely debated and a key theme in hominin evolutionary studies. We review archeological, fossil, environmental, and genetic data to evaluate the current state of knowledge on the dispersal of Homo sapiens out of Africa. The emerging picture of the dispersal process suggests dynamic behavioral variability, complex interactions between populations, and an intricate genetic and cultural legacy. This evolutionary and historical complexity challenges simple narratives and suggests that hybrid models and the testing of explicit hypotheses are required to understand the expansion of Homo sapiens into Eurasia.

Coastlines, Submerged Landscapes, and Human Evolution: The Red Sea Basin and the Farasan Islands

ABSTRACT We examine some long-standing assumptions about the early use of coastlines and marine resources and their contribution to the pattern of early human dispersal, and focus on the southern Red Sea Basin and the proposed southern corridor of movement between Africa and Arabia across the Bab al-Mandab Straits. We reconstruct relative sea levels in light of isostatic and tectonic effects, and evaluate their paleogeographical impact on the distribution of resources and human movement. We conclude that the crossing of the Bab al-Mandab posed little significant or long-lasting physical or climatic barrier to human transit during the Pleistocene and that the emerged continental shelf during periods of low sea level enhanced the possibilities for human settlement and dispersal around the coastlines of the Arabian Peninsula. We emphasize the paleogeographical and paleoenvironmental significance of Pleistocene sea-level change and its relationship with changes in paleoclimate, and identify the exploration of the submerged continental shelf as a high priority for future research. We conclude with a brief description of our strategy for underwater work in the Farasan Islands and our preliminary results.

The Red Sea, Coastal Landscapes, and Hominin Dispersals

The Red Sea has typically been viewed as a barrier to early human movement between Africa and Asia over the past 5 million years, and one that could be circumvented only through narrow exit points at either end, vulnerable to blockage by physical or climatic barriers (Fig. 1). It is one of several significant obstacles cutting across ‘savannahstan’ (Dennell and Roebroeks, 2005), a broad swathe of herbivore-rich savannah and grassy plains that began to extend over a vast area stretching from West Africa to China with climatic cooling from at least 2.5 Ma, and a key macro-environmental context for early hominin dispersal1. However, this concept of the Red Sea Basin as a barrier should not obscure the fact that its coastal regions also hold considerable potential attractions for early human settlement, especially under climatic conditions wetter than today, including a complex tectonic and volcanic topography not unlike that of the African Rift, capable of providing localized fertility for plant and animal life, tactical opportunities for pursuit of herbivores and protection from predators (King and Bailey, 2006), along with inshore and intertidal marine resources.

Tectonics and human evolution

The authors propose a new model for the origins of humans and their ecological adaptation. The evolutionary stimulus lies not in the savannah but in broken, hilly rough country where the early hominins could hunt and hide. Such ‘roughness’, generated by tectonic and volcanic movement characterises not only the African rift valley but probably the whole route of early hominin dispersal.

Landscapes and their relation to hominin habitats: Case studies from Australopithecus sites in eastern and southern Africa

We examine the links between geomorphological processes, specific landscape features, surface water drainage, and the creation of suitable habitats for hominins. The existence of mosaic (i.e., heterogeneous) habitats within hominin site landscape reconstructions is typically explained using models of the riverine and gallery forest settings, or the pan or lake setting. We propose a different model: the Tectonic Landscape Model (TLM), where tectonic faulting and volcanism disrupts existing pan or river settings at small-scales (∼10-25 km). Our model encompasses the interpretation of the landscape features, the role of tectonics in creating these landscapes, and the implications for hominins. In particular, the model explains the underlying mechanism for the creation and maintenance of heterogeneous habitats in regions of active tectonics. We illustrate how areas with faulting and disturbed drainage patterns would have been attractive habitats for hominins, such as Australopithecus, and other fauna. Wetland areas are an important characteristic of surface water disturbance by fault activity; therefore we examine the tectonically-controlled Okavango Delta (Botswana) and the Nylsvley wetland (South Africa) as modern examples of how tectonics in a riverine setting significantly enhance the faunal and floral biodiversity. While tectonic landscapes may not have been the only type of attractive habitats to hominins, we propose a suite of landscape, faunal, and floral indicators, which when recovered together suggest that site environments may have been influenced by tectonic and/or volcanic activity while hominins were present. For the fossil sites, we interpret the faulting and landscapes around australopithecine-bearing sites of the Middle Awash (Ethiopia) and Makapansgat, Taung, and Sterkfontein (South Africa) to illustrate these relationships between landscape features and surface water bodies. Exploitation of tectonically active landscapes may explain why the paleoenvironmental signals, anatomy, diets, as well as the fauna associated with Australopithecus appear largely heterogeneous through time and space. This hypothesis is discussed in light of potential preservation and time-averaging effects which may affect patterns visible in the fossil record. The model, however, offers insight into the landscape processes of how such habitats are formed. The landscape features and range of habitat conditions, specifically the wetter, down-dropped plains and drier, uplifted flanks persist in close proximity for as long as the fault motion continues. The Tectonic Landscape Model provides an alternative explanation of why mixed habitats may be represented at certain sites over longer timescales.

Caves, palimpsests and dwelling spaces: examples from the Upper Palaeolithic of south-east Europe

Abstract Deposits in caves and rock-shelters typically occur in the form of low-resolution palimpsests or time-averaged deposits, resulting from the superimposition of repeated and variable episodes of occupation, low rates of sedimentation and mixing by natural and anthropogenic processes. Despite the development of an impressive array of analytical techniques to disentangle these palimpsests into their constituent episodes of occupation, high resolution chronologies and detailed snapshots of activity areas and spatial organization have proved elusive. Here we suggest that, rather than seeing palimpsests as a problem, we take them as they are, as mixtures of materials that may have been actively recognized as such by the prehistoric occupants and deliberately enhanced, providing both physical resources that could be recycled for subsequent use and material cues for a sense of time and place. We illustrate this approach through a comparison of the spatial and material structure of four Upper Palaeolithic cave deposits in Southeast Europe, focusing on hearths and hearth-related distributions of material as clues to the active role of palimpsests in determining the use histories of different places.

Complex topography and human evolution: the missing link

Why did humans walk upright? Previous models based on adaptations to forest or savannah are challenged here in favour of physical incentives presented by steep rugged terrain—the kind of tectonically varied landscape that has produced early hominin remains. “Scrambler man” pursued his prey up hill and down dale and in so doing became that agile, sprinting, enduring, grasping, jumping two-legged athlete that we know today.

Active tectonics and land-use strategies: a Palaeolithic example from northwest Greece

Tectonic movements – continuously re-moulding the surface of the earth over the inexorable activity of underlying plate motions – are rarely taken into account when assessing landscape change, except as an exotic hazard to human life or a temporary disruption in longer-term trends. Active tectonics also create and sustain landscapes that can be beneficial to human survival. The tectonic history of northwest Greece shows Palaeolithic sites located to take advantage of tectonically created features at both local and regional scales.

A response to Richards and Schulting

We welcome the comments of Mike Richards and Rick Schulting; however, rather than attempting to close the debate on the isotope evidence and the Mesolithic-Neolithic transition, as suggested in their introduction, we agree that the issues raised should be widely discussed and subject to critical and well informed scrutiny. We certainly did not attempt a ‘simple outright denial of the validity of one of the methods of analysis’ (i.e. stable isotopes); rather we wished to make the point that interpretations have to take into account uncertainties associated with the measurements. We have been pleased by the discussion that our article has invoked: two published responses (Barbarena & Borrero 2005; Hedges 2004) and numerous personal communications which have been supportive and critical in

Concepts of resource exploitation: Continuity and discontinuity in palaeoeconomy

Abstract This paper focuses on the underlying concepts that have influenced explanations of long‐term economic change associated with the development of prehistoric agriculture. Existing classificatory schemes, derived from the hunter‐gatherer/farmer dichotomy or from concepts of resource husbandry, tend to emphasise discontinuities in the process of economic change or continuities, respectively. An attempt to reconcile these contradictory viewpoints is made through the elaboration of a unifying scheme for classifying man‐resource relationships, based on a polarity between opportunistic and controlled patterns of exploitation, and between direct and indirect patterns. The developmental implications of this scheme are briefly examined.