Over the last century, morality has been thoroughly examined through evolutionary biology, psychology, and cognitive neuroscience. However, little work has concerned itself with systematically unifying these levels of inquiry. Here, we propose thermoethics as a framework to fill this gap. Central to this approach is the idea that moral processes are fundamentally tied to the conservation and expenditure of metabolic energy. By integrating physiological concepts like homeostasis and allostasis within the context of prosocial behaviour and cognition, we demonstrate how the thermodynamics associated with pain and stress can be understood as energy-costly processes, while pleasure and relief can be understood as energy-saving processes. We show how studying these metabolic dynamics can serve explanations in the evolution of morality, the mechanisms underpinning moral cognition, and ethical theorizing. This interdisciplinary perspective, we argue, offers a robust, physics-consistent foundation for future research in naturalized ethics, highlighting the unifying links between neurophysiological processes and moral phenomena.