Iver Neumann argues that International Relations (IR) is going to have to engage with a broader set of empirical data and wider inter-disciplinary insights, especially from evolutionary biology. I endorse the debate and extend the challenge, making four key points: (1) our empirical data must extend to the deep origins of human societies, and look more at policy successes rather than failures; (2) our scientific toolkit must integrate rather than differentiate psychology and biology, because the former is in large part a product of the latter; (3) evolution continues to be misinterpreted, especially in the condemnation of functionalism, the myth of biological determinism, the perceived lack of relevance to IR theory, and the idea that social facts cannot have biological roots; and (4) there are other issues of more genuine importance, including the levels of analysis problem (getting from the biology of individuals to the behaviour of states), and the levels of selection problem (the predictions of group selection and individual selection for human nature). I conclude that, despite big challenges of communication and collaboration, the benefits of integration with the natural sciences far outweigh the benefits of disciplinary isolation, offering new knowledge, methods, consilience, and parsimony that will help IR to flourish rather than flounder in the Age of Biology.