Helmuth Plessner's Levels of Organic Life and the Human [Die Stufen des Organischen und der Mensch, 1928] is one of the founding texts of twentieth century philosophical anthropology (understood as philosophical reflection on the fundamental characteristics of the human lifeform). It is argued that Plessner's work demonstrates the fundamental indispensability of the qualitative humanities vis-à-vis the natural-scientific study of man. Plessner's non-reductionist, emergentist naturalism allots complementary roles to the causal and functional investigations of the life sciences and the phenomenological and hermeneutic interpretation of the phenomenon of life in its successive levels and stages. Within this context, human agency can be understood as a higher-order property of organic life, which act by the selective activation of lower-level psychophysical powers. Plessner's three "anthropological laws' are used to situate the notion of practical self-understanding in between two extremes: deterministic views that deny human freedom and responsibility and views that ascribe an unrealistic amount of autonomy to human beings.