This article analyzes the power of ambiguous metaphors to present scientific novelty. Its focus is a series of papers by the prominent population biologist W. D. Hamilton in which he redefined the meaning of biological altruism. In particular, the article draws on Kenneth Burke's dramatistic pentad to examine why suggestions of motive are so pervasive in Hamilton's representation of genetic evolution and what epistemological consequences result from this rhetorical choice. Specifically, the metaphorical language of motive allows Hamilton to represent genes ambiguously and simultaneously as both the agents of evolutionary action and as the agency or mechanism by which organism agents act. The textual ambiguity generated by the agent-agency metaphors both reflects and constructs a conceptual ambiguity in the way evolutionary processes are theorized. Analysis of Hamilton's rhetoric thus suggests the productive function of ambiguous metaphors in highly technical scientific texts.