Over the last few decades, behaviorism as a philosophy of the science of psychology, especially in the field of behavior analysis and related areas, has diversified to the point that scholars from inside and outside the field are often confused about what exactly behaviorism is. The aim of this study is to analyze how such diversification of behaviorism has arisen over time and what factors might have contributed to it using evolutionary biology's concept of adaptive radiation as an analogical process. Diversification of behaviorism has occurred in many areas over time as behaviorism has extended its field of practice. Although some characteristics of behaviorism remained, other characteristics were modified. One such characteristic that went through extensive modification is the agent-free approach to the analysis of behavior: the agent problem. This approach has met criticism from inside and outside the field and has been under a strong selective pressure. The present article discusses how the agent problem in a different niche has shaped behaviorism into new forms that we see today.