The main goal of this paper is to show how, in the study of action, contemporary American environmentalism absorbed intact the key concept of the nativism it displaced in the period between 1920-1935. The nature-nurture antagonism has been enacted many times in the history of psychology, in many guises. In the study of sensation and perception, of knowledge, of general mental capacity, of chronological development, of language, of individual differences in any of the foregoing, the historian can find the competing claims of empiricists and nativists, often in repeating cycles of intellectual fashion. This paper focuses, however, on just one of the many disputed areas-the study of action or behavior-and further limits itself geographically and chronologically to America in the period roughly between the two World Wars. This instance of the nature-nurture polarity beckons historical study, first of all, because of its relative clarity and definiteness. A second reason for study is that there are unmistakable signs of the return trip of the pendulum towards the nativist side. Contemporary findings and theories in the study of cognitive development, language, visual space perception, schizophrenia, human learning ability, and the growing popularity of ethological research epitomize the shifting bias, away from environmentalist and towards nativist accounts. In the case of the analysis of behavior, however, the return trip may be unexpectedly short, for it can be shown that there was substantially less actual movement of the pendulum when behaviorism prevailed over the instinct doctrine in the early 1920's. In the space of just a few years, the established instinct theories of behavior largely vanished, yielding to the onslaught of American behaviorism, with its ostensibly radical environmentalism. The two schools at times confronted each other literally, as when the instinct theorist, William McDougall debated, in 1924, with John B. Watson, the founder of behaviorism as a self-conscious schoo
