More than 25 years ago, C. K. Brain introduced the idea that there might be causal links between Neogene African climate change and major events in human evolution. Since that time, there have been 1) consistent advances in the study of the deep-sea paleoclimate record; 2) a more sophisticated understanding of the impact of tectonic and orbital forcing on African paleoenvironmental conditions; and 3) the expanded recovery of an increasingly refined terrestrial vertebrate fossil record. Vrba's turnover pulse hypothesis, which was based on purported rapid changes in Plio-Pleistocene vertebrate community structure, was an important early step in organizing some of these data sets into a coherent scenario of the mechanisms that drove human evolution. However, improved faunal samples from East Africa do not document the abrupt bursts of evolution predicted by the turnover pulse hypothesis (e.g., Behrensmeyer et al., Science 1997;278:1589). Undaunted, researchers forge ahead, workshops and symposia convene, and scholarly tomes are published. In the process, the hypothesis that environmental (including climatic) change is linked to speciation has become as mundane as it is profound. Two currently prominent and competing variants of this theme are Potts's variability selection hypothesis and the environmental forcing hypothesis of Bobe Β΄and colleagues.
These issues were the subject of a recent special journal issue (''African Paleoclimate and Human Evolution, '' Journal of Human Evolution 2007;53:443). Considering the storied context of the topic (much condensed here), the introductory remarks of editors Maslin and Christensen, ''Results presented in this volume may represent the basis of a new theory of early human evolution in Africa,'' are laid bare as hyperbole. The primary importance of the results presented in the Maslin and Christensen issue is not theoretical. Its value is instead as a collective, datarich summation that parses the relative contributions of tectonics, orbital forcing, and global climate in creating local African environmental conditions under which hominids evolved throughout the Plio-Pleistocene.
In that perspective, Hominin Environments in the East African Pliocene, edited by Bobe Β΄et al., can be V