There are currently no fully ordained nuns in the Theravada Buddhist system. The doctrinal reason is because ordination ritual guidelines require the presence of senior nuns (of which, due to the dissolution of the nun orders, there are none) at a female's ordination. A more critical reason offered by feminists is that sexism (textual, traditional, and institutional) maintains the status quo. We argue that the Ritual Form Hypothesis of McCauley and Lawson (2002) best explains the continued lack of nun ordinations by making claims about cognitive constraints on ritual efficacy. Furthermore we predict that the institutional prevention of full nun ordinations will persist unless a new superhuman agent (i.e. a new Buddha) emerges with a new doctrine or unless Buddhists discover a different teaching that stipulates new conditions for ordination. Both are unlikely, however, given Theravada's theological conservatism.