The term "continuity" is derived from the French, continuite, and the Latin, contuitas-tatis, for continuous. Dictionary definitions refer to "the state of being continuous," "an unbroken succession," or "a logical sequence." Thus, continuity is used to describe a sequence of related events or phenomena. In behavior analysis, the term is typically used in a nontechnical manner to refer to the assumption of a similarity of psychological principles between nonhumans and humans. Indeed, this assumption might be considered a cornerstone of the behavior-analytic approach to science. According to Skinner (1953):
Human behavior is distinguished by its complexity, its variety, and its greater accomplishments, but the basic processes [shared with nonhumans] are not therefore necessarily different. Science advances from the simple to the complex; it is constantly concerned with whether the processes and laws discovered at one stage are adequate for the next. It would be rash to assert at this point that there is no essential difference between human behavior and the behavior of lower species; but until an attempt has been made to deal with both in the same terms, it would be equally rash to assert that there is. (p. 38)
The assumption of continuity between nonhumans and humans has guided and continues to guide the research activity of behavior analysts despite there being little evolutionary justification for such an assumption. The evolutionarily sensible form of continuity holds that "new contains old" and thus it can not be assumed that "old contains new." Evolutionary theory would be rendered absurd if this were the case because evolutionary continuity flows forward in time, not backward. Metaphorically, studying distantly related species is akin to viewing the tips of evolutionary branches, not the rungs of a single evolutionary ladder. As such, evolution progresses outward, from the point at which different species differentiated, to the present containing features of both new and old. In this way, discontinuity between humans and nonhumans would in no way contradict a biologically sensible form of the continuity assumption (Hayes, Barnes-Holmes, & Roche, 2001a, p. 145). Indeed, although biological continuity provided the inspiration for the evolutionary postulation of psychological continuity between species, it does not itself depend on the assumptions of evolution for justification. Thus, biological continuity would assume no difference between species, pending empirical evidence to the contrary. We will return to this issue in greater detail. The important point here is that uncertainty and disagreement over the precise nature and status of the continuity assumption may have contributed to possible confusion within the field. In addition, recent empirical and conceptual advances in the analysis of derived relational responding suggest that a fresh look at the issue of continuity may be warranted.
The present paper will first outline the traditional behavior-analytic view of nonhuman-human (1) continuity and highlight its pragmatic research features. Next, we will summarize the predominant use of the continuity assumption in research on basic tasks such as schedules of reinforcement and discuss the role it has played in recent discussions of nonhuman-human differences. Then, we will explore the possibility that behavioral principles different from those already discovered in research with nonhumans may be needed to explain complex human behavior, most notably in the experimental analysis of verbal behavior and derived stimulus relations. Finally, we will conclude with a pragmatic view of the future of the continuity assumption.
Behavior Analysis and The Continuity Assumption
In "The Descent of Man," Charles Darwin proclaimed that "there is no fundamental difference between man and the higher mammals in their mental faculties" …