The Aristotle-Kant tradition requires that autonomous activity must originate within the self and points toward a new type of causation (different from natural efficient causation) associated with teleology. Notoriously, it has so far proven impossible to uncover a workable model of causation satisfying these requirements without an increasingly unsatisfying appeal to extra-physical elements tailor-made for the purpose. In this paper we first provide the essential reason why the standard linear model of efficient causation cannot support the required model of agency: its causal thread model of efficient causation cannot support the core requirement that an action is determined by, and thus an expression of, the agent’s nature. We then provide a model that corrects these deficiencies, constructed naturalistically from within contemporary biology, and argue that it provides an appropriate foundation for all the features of genuine agency. Further, we provide general characterisations of freedom and reason suitable to this bio-context (but that also capture the core classical conceptions) and show how this model reconciles them.