In his closet-drama Cain, Byron connects extinction to a nascent, and surprising, catastrophic evolutionism that argues the world's current human inhabitants will gradually destroy the whole of their own species and be replaced with newer, updated life forms of an entirely different, unknown sort. As I show, an unaccounted for aspect of the play—Cain's moral outrage over the sacrifice of animals—offers a possible intervention in this cataclysmic cycle. For Byron, it seems, ontological replacement will only occur if humans refuse to stop killing non-humans as represented by the animal sacrifices that induce Cain's fratricide, actions that humans nonetheless seem ironically incapable of ending. Examining how Agamben's biopolitics help frame Cain's actions, I explicate how Cain's actions also point out the limits of Agamben's conceptualization of biopolitics and push into speculative realist territory. The play ultimately offers a non-anthropocentric vision of life on earth.