环境变异及其对人类进化的作用

ENVIRONMENTAL VARIABILITY AND ITS EFFECT ON HOMINID EVOLUTION

Early hominids have long been considered to have evolved in response to a directional shift from forested to open habitats (e.g., woodland, savanna grassland,glaciated terrain). Long-term paleoenvironmental records during the span of hominid evolution, however, contradict the idea of a simple directional trend followed by open-habitat stability. Rather, evidence from deep ocean cores, paleovegetation, and paleolakes all suggest a high degree and erratic pace of environmental fluctuation. The degree of fluctuation was higher during the period of hominid evolution than any earlier time during the Cenozoic. Thus adaptation to disparity, or to the conflicting demands posed by natural selection, may provide a better explanation of hominid evoluReceived April 27, 1995Submitted for the special publication commemorating the 65th Anniversary of the IVPP, Academia Sinica, China. tion than adaptation to a single directional trend or stable environment. An example from the Pleistocene of southern Kenya illustrates how species survival and change may have been affected by environmental variability.