--- - |2 In the context of evolutionary theory, behavior is the interaction between the organism and its environment. Two implications follow: (a) behavior takes time; and (b) behavior is defined by its function. That behavior takes time implies that behavioral units are temporally extended patterns or activities. An activity functions as an integrated whole composed of parts that are themselves smaller‐scale activities. That behavior is defined by its function implies that behavior functions to change the environment in ways that promote reproductive success. Phylogenetically important events (PIEs) are enhanced or mitigated by activities they induce as a result of natural selection. Induction explains all the phenomena that have traditionally been explained by reinforcement. This multiscale view replaces discrete responses and contiguity with multiscale activities and covariance. A PIE induces operant activity as a result of covariance in the form of a feedback relation between the activity and the PIE. A signal (conditional inducer) induces PIE‐induced activities as a result of covariance between the PIE and the signal. In an ontological perspective, behavior is a process, and an activity is a process individual. For example, ontological considerations clarify the status of delay and probability discounting. A true natural science of behavior is possible. - Journal of the Experimental Analysis of Behavior, EarlyView.