Developmental science is undergoing a true Kuhnian paradigm shift, away from early 20th century gene-based ideas of instinct toward modern biophysical ideas of holism and epigenesis. These ideas can be traced from the early work of Zing Yang Kuo to the early- and mid-20th century writing of J. R. Kantor and T. C. Schneirla and the later work of Gilbert Gottlieb, Willis Overton, and Richard M. Lerner. All emphasized experiences through development as the sources of behavior and understood psychology to be a biospychosocial, natural, science. The contemporary iteration of this is referred to relational developmental systems.