Evolutionary Behavioral Sciences11.1 (Jan 2017): 53-62. When veterans return from war, many experience difficulties with interpersonal trust, particularly those suffering from posttraumatic stress disorder (PTSD). While proximate explanations for veteran mistrust have been proposed, the ultimate explanations lie within our evolved psychology, shaped as it was by a long evolutionary history of coalitionary violence between men. The exchange of signals of mutual commitment, especially in the context of violence, reflects important features of our evolved psychology. While such exchanges may have typified the small, cohesive social environments in which our brains evolved, those exchanges are comparatively lacking in the modern societies to which veterans return, resulting in what biologists describe as a phylogenic mismatch. This mismatch may underlie a variety of veteran reintegration problems. Though largely neglected in the literature, evolutionary explanations for PTSD sequelae among veterans offer invaluable insights for clinicians, family members, friends, or employers interfacing with veterans during their reintegration into peacetime civilian life. (PsycINFO Database Record (c) 2017 APA, all rights reserved) (Source: journal abstract) To read the full article, log in using your NHS OpenAthens details.