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Dynamic Landscapes, Coastal Environments and Human Dispersals

Final Report Summary - DISPERSE (Dynamic Landscapes, Coastal Environments and Human Dispersals)

Human evolutionary change during the past 2 million years has occurred in landscapes subject to rifting, faulting, volcanoes, earthquake activity, and sea-level change oscillating through a vertical amplitude of >100m in response to successive ice ages. These changes are especially prominent in the regions of earliest human evolution and dispersal: the African Rift, Red Sea, Middle East and Mediterranean. Our project aimed to investigate the causal links between these processes.

The fundamental challenge is the difficulty of reconstructing ancient landscapes in regions of massive geological change. We tackled this in two ways. First, we adapted methods from the new field of ‘tectonic geomorphology’ developed by earth scientists to understand landscapes subject to repeating earthquakes. We used satellite imagery and field observations to identify the underlying geodynamic history of physical landscapes, and computer modelling and dating of faulting, shorelines and volcanic lava flows to ‘wind back’ the evolution of the landscape to what it would have looked like at earlier periods. Secondly, we carried out underwater exploration on the Red Sea continental shelf with a fully equipped research ship to explore the nature of the terrestrial landscapes exposed down to depths of −130m.

We articulated and tested a new hypothesis. The ‘complex topography hypothesis’ proposes, counter-intuitively, that geological instability continuously renews complex topography with significant attractions for early humans: fault scarps and volcanic lavas that trap sediments and water to form local areas of fertility and renew soil nutrients; rough topography of tactical advantage in avoiding predators or accessing elusive prey mammals; and conditions that reinforce the selective advantages of a bipedal gait to facilitate scrambling over rough terrain. This hypothesis helps to explain why the African Rift favoured the emergence of the genus Homo and predicts that early dispersals out of Africa would have targeted similar environments. As a test, we compared landscape reconstructions with the distribution of archaeological sites and hominin fossils and demonstrated correlations at continental, regional and local scales. In SW Arabia we discovered over 90 early Stone Age sites, dating back at least 1 million years, through satellite and ground survey in a volcanic and coastal setting, adding support to the idea that this was a proximate zone for early human expansion out of Africa.

Underwater results show that the southern Red Sea at lowest sea level comprised a now-submerged 200 km-wide coastal lowland divided by a narrow sea channel, with complex topography and fault-bounded, sediment-filled lake basins, attractive to herd animals and their human hunters during periods of maximum climatic aridity in adjacent hinterlands. Short sea-crossings and offshore archipelagos would have favoured early experiments in seafaring, supporting the hypothesis of expansion across sea channels and through coastal regions fuelled by adaptations integrating marine and terrestrial resources.

We have not yet discovered archaeological sites in our underwater searches, but investigation of the abundant shell mounds on the modern coastline – the most visible material record of coastal settlement, and known only from 6500 years ago when postglacial sea level rise reached the modern level – provides an analogue for where coastal sites should be found on underwater shorelines. Seasonality analyses show that the shells were collected as food throughout the year with a peak in the most arid seasons when other food resources were scarce, indicating a simple and probably very ancient adaptation to semi-arid environments. Further investigation of these submerged landscapes remains one of the greatest challenges for the future.

Our research is also relevant to present-day problems: in demonstrating the geological basis for mineral-deficient soils and their impact on modern animal and human disease, and in refining understanding of sea level change and its human impact.