RECONCILING DIVERSE PALEOENVIRONMENTAL RECORDS LINKED TO EARLY HOMININ EVOLUTION IN EQUATORIAL AFRICA

Since Darwin situated humans in an evolutionary framework, much discussion has focused on the role of the environment in mediating or directing the course of human evolution in Africa during the late Neogene. Drawing on diverse paleoenvironmental datasets of varying quality, scale, and relevance, hominin evolution has traditionally been interpreted in a somewhat generalized environmental framework, characterized primarily by increasing aridity and seasonality periodically punctuated by pulses or intervals of environmental change, inferred largely from global climatic records. However, emerging paleoenvironmental evidence from equatorial Africa has revealed complex patterns of habitat heterogeneity and persistent ecological flux throughout this interval.

If the goal is to assess causality, the scale and quality of paleoenvironmental data as well as specific links to hominin contexts must be commensurate with the adaptive questions at hand. In this respect, assessments must either be based on local environmental reconstructions associated with hominins and their faunal and floral communities or on global or regional proxies with well-established links or controls on local hominin ecosystems. At the local level there is a need to move beyond basic notions of heterogeneity and develop means of distinguishing and characterizing the specific nature of ‘mosaic’ habitats. This requires developing proxy datasets that sample at high resolution with controls for time averaging, rarefaction, diagenesis and other biasing factors. In addition the data must incorporate a lateral component to capture the spatial dimension of habitat heterogeneity, be comparable across sites or basins, and be available to document at all the sites. These remain difficult demands.

Perhaps a more important direction is a conceptual one – basically to replace emphasis on large-scale environmental change or trends by more inclusive conceptual models that also incorporate the dynamic and cyclical environmental fluctuations operating continually on hominin habitats in Africa at small scales. Rather than assimilating environmental data to develop models of human evolution, the approach should focus more simultaneously generating hypothesis about how evolution happens to help direct the collection of relevant paleoenvironmental data.