This paper addresses the critical and transformative power of Nietzsche's socio-physiology of the self. In the Nachlass of 1880-1882 Nietzsche develops a socio-physiological (pre-) history of the individual, which is reconstructed in this paper as a counter-argument to the modern conception of autonomy as the freedom to choose one's concept of the good on the part of an asocial, substantial Subjekt. On the one hand, Nietzsche's physiological reflections on the (pre-) historical and social sources of the self imply a devastating critique of the asocial, antecedently individuated person; on the other hand, they point towards an alternative concept of the sovereign person, one whose capacities for autonomous thought and agency depend on specific relations of measured antagonism both between and within us as "dividua". These arguments are developed along three main lines of thought: I. On the (pre-)history and social constitution of our capacities as sovereign individuals; II. On the social sources of moral phenomena (as internalisations of social norms); and III. The physiological destruction of the substantial moral Subjekt and the physiological reconstruction of the Subjekt as dividuum.