The resemblance among operant shaping, cultural evolution, and genetic evolution appears clearly only in the light of a general concept of evolutionary process. Evolutionarily significant variation occurs among substitutable variants within a pool. These variants are defined by differences in their environmental effects. Although the metaphor of copying characterizes recurrence in genetic evolution, replication is only one type of recurrence. In cultural and operant evolution, mechanisms like stimulus control and induction cause the recurrence of the variants.
Selection occurs when recurrence is differential.
Differences in environmental effects produce differences in recurrence, and those differences feed back to affect the composition of the pool of variants. This general view of evolutionary process clarifies the distinction between proximate and ultimate explanations of behavior. Genetic, cultural, and operant evolution all admit of this distinction, because they all distinguish advantageous mechanisms from a history of advantage.