Gilbert Gottlieb's theory of probabilistic epigenesis is a fertile ground for further theoretical construction in developmental science. It fills the gap in the domineering empiricism and honoring of inductive generalization that dominates psychology in the beginning of the 21st century, by offering a basic deductive framework for guiding the efforts of developmental science. Further development of his theory takes the form of (a) explicating the propensity notion of probability in his model, (b) extending his multi-level system to include psychological and social levels of organization, and (c) adopting the core notion of systemic catalytic causality for explanations of developmental processes.