Abstract
Evolution means different things at different stages of development. Higher stage explanations for it are downward assimilated at lower stages. Different scientific explanations for evolution also reflect different stages of development. Hierarchical complexity of tasks in evolution is a behavioral analytic explanation. It is selection processes of various kinds in tandem with changes in selection tasks' orders of hierarchical complexity. There is neither teleology nor evolutionary favoring of the highest stages of performance. Selection tasks at higher orders of complexity increasingly decenter at all scales of behaviors from thought to history's social periods. These processes account for sociopolitical conflicts over evolution.