Low Mood: Evolution, Cognition, and Disorder

In this thesis, I offer a novel, overarching account of the cognitive architecture, evolution, and disorders of the capacity for low mood. First, I offer novel arguments for the propitiousness theory, according to which the proper function of the low mood system (LMS) is to limit resource expenditure in unpropitious circumstances. Following this, I develop an original account of the intentional content of low mood, according to which low mood has the following indicative-imperative content: Good events are, on average, less likely to occur than bad events & Limit [the subject’s] resource expenditure! Next, I argue that the LMS takes input from numerous sensory, interoceptive, and affective systems, but that higher cognition can only effect low mood indirectly—namely, by triggering low-mood-inducing emotions. Finally, I argue that (a) disorders are necessarily constituted by dysfunctional systems (systems that fail to carry out their proper function), (b) most cases of depression (severe, long-lasting low moods) are activations of properly functioning LMSs, and therefore (c) most cases of depression are not in fact disorders.