17 Tropical and temperate seasonal influences on human evolution

Climatic and subsequent habitat change has often been invoked as a driving force of evolutionary change in hominins, mammals, and other taxa (Vrba 1988a, 1988b, 1992, 1995; Bromage & Schrenk 1999; Potts 1998; Bobe & Eck 2001; Janis et al. 2002). Global climatic change in the mid Pliocene Epoch has been suggested as a cause for hominin speciation events (Vrba 1995) and is correlated with changes in dentition and jaw morphology of two hominin lineages (Teaford & Ungar 2000). Climatic change also influences seasonality, such that drying trends, for example, likely instigate short wet seasons, while the reverse is also true. Although Foley (1987) indicated that seasonal differences were likely important in determining hominin foraging effort, and Blumenschine (1987) posited a dry-season scavenging niche for Pleistocene hominids, little attention has been given to how seasonal changes over time might contribute to differences among hominin behavioral adaptations. Seasonal changes refer to changes in the lengths of regular four-season patterns in temperate climates or wet and dry seasonal differences in the tropics over geological time. Evolutionary changes in fossil hominins are detected through changes in morphology that represent different behavioral adaptations. Fossil hominin diets are inferred from comparisons with extant primates in features such as tooth size (Hylander 1975; Kay 1984; Ungar & Grine 1991), molar