Variability selection in hominid evolution (vol 7, pg 81, 1998)

Variability selection (abbreviated as VS) is a process considered to link a daptive change to large degrees of environment variability. Its application to hominid evolution is based, in part, on the pronounced rise in environm ental remodeling that took place over the past several million years. The V S hypothesis differs from prior views of hominid evolution, which stress th e consistent selective effects associated with specific habitats or directi onal trends (e.g., woodland, savanna expansion, cooling). According to the VS hypothesis, wide fluctuations over time created a growing disparity in a daptive conditions. Inconsistency in selection eventually caused habitat-sp ecific adaptations to be replaced by structures and behaviors responsive to complex environmental change. Key hominid adaptations, in fact, emerged du ring times of heightened variability. Early bipedality, encephalized brains , and complex human sociality appear to signify a sequence of VS adaptation s-i.e., a ratcheting up of versatility and responsiveness to novel environm ents experienced over the past 6 million years. The adaptive results of VS cannot be extrapolated from selection within a single environmental shift o r relatively stable habitat. If some complex traits indeed require disparit ies in adaptive setting (and relative fitness) in order to evolve, the VS i dea counters the prevailing view that adaptive change necessitates long-ter m, directional consistency in selection.