TERRESTRIAL SYSTEM RESPONSE TO GLOBAL CHANGE: IMPLICATIONS FOR HOMININ EVOLUTION

Developments in hominin evolution over the past eight million years, including morphological change, cultural advances, and range expansion, took place within a context of dynamic terrestrial landscapes. Terrestrial systems which shaped hominin habitats through time responded to a variety of controlling factors, including tectonics, volcanism, and climate. Recent developments have demonstrated that early models of environmental influence on hominin evolution were overly simplistic. However, the geological record provides a detailed environmental framework into which trends and events of the hominin record can be understood.

Late Miocene (Tortonian-Messinian) localities demonstrate the development of the early African savanna biome along with markedly xeric and mesic counterparts. Long-term stability in some regions contrasts with major landscape shifts elsewhere, and ultimate disruption associated with Messinian desiccation. Pliocene fluvial landscapes exhibit long-term stability, punctuated by brief tectonic and volcanic disruptions. Significant drying is roughly coincident with the Plio-Pleistocene boundary, with basinal responses determined by local threshold effects. Diversification and extinction events at this time, including the origin of the large form of genus Homo, reflect a combination of increased selective pressures with an apparent release of biogeographic constraints. Terrestrial routes out of Africa may have been temporally limited, but hydrographic corridors, such as the Levantine Rift, offered attractive habitats for longer duration.

Patterns of character and change in global climate are recorded in responses of terrestrial systems throughout this record, although commonly overshadowed by local effects. Long-term trends and variation in the tempo of climatic oscillations were important to terrestrial systems, but a more critical factor may have been the relationship of climatic variability to thresholds in terrestrial system response.