HOMININ EVOLUTION IN SETTINGS OF STRONG ENVIRONMENTAL VARIABILITY

Interest in the connections between climate change and human evolution has shifted the focus of paleoenvironmental research toward environmental dynamics, i.e., the nature and tempo of climate and landscape variability recorded in long stratigraphic sequences, with less emphasis on static habitat reconstructions. The interaction among insolation cycles and episodic tectonic effects is especially apparent in the paleoenvironmental records of the East African Rift System. A concise summary of key hypotheses linking African climate and evolution helps to define four criteria necessary in establishing cause-and-effect explanations of hominin evolutionary responses to environmental dynamics: (1) correlation; (2) associated biotic responses; (3) tested evolutionary mechanisms; and (4) analyses of hominin adaptations that point to the action of specific evolutionary mechanisms.

Examples will show how these criteria are fulfilled relevant to variability selection explanations of the Plio-Pleistocene Oldowan expansion and the middle Pleistocene transition from Acheulean to Middle Stone Age. Especially relevant to these explanations is the framework of alternating high- and low-climate variability in tropical Africa, with key events in hominin evolution concentrated in the predicted longest intervals of high climate variability. A synthesis of environmental indicators cautions against an exclusive focus on the end members of environmental fluctuation (driest or wettest, warmest or coolest), and argues for the impact of the entire range of amplified variability in shaping evolutionary change. New theoretical modeling and simulations, furthermore, point to how adaptive versatility is selected as environmental variability is amplified. A relatively novel view thus emerges in which important changes in stone technology, life history, sociality, and other aspects of hominin behavior are understood as adaptive responses to heightened habitat instability.

This research has been supported by the Smithsonian’s Human Origins Program, the Peter Buck Fund for Human Origins Research, and the NSF HOMINID Program (BCS-0128511), with fieldwork permits and logistics supported by the National Museums of Kenya.