A hundred years ago, the Journal of Comparative Psychology began being published and currently stands as the longest-running science journal devoted to the study of animal behavior. In that same year, 1921, a paper was published in the Journal of Philosophy that was foundational to our field of study—“Giving up Instincts in Psychology” by Zing-Yang Kuo. This brief essay discusses some of the main arguments of Kuo’s article and how they have extended into today’s thinking and empirical work on behavioral development. The essay emphasizes his ideas about the need to study neophenotypes to understand the range of behavioral possibilities and to assess nonobvious sources of experience in the development of species-typical behavior. (PsycInfo Database Record (c) 2021 APA, all rights reserved)