Critical Discourse Analysis has recently begun to consider the implications of research in Evolutionary Psychology for political communication. At least three positions have been taken: (i) that this research requires Critical Discourse Analysis to re-examine and defend some of its foundational assumptions (Chilton 2005); (ii) that this research provides a useful explanatory framework for Critical Discourse Analysis in which questions can be addressed why might speakers pursue particular discursive strategies and why they might be so persuasive (Hart 2010); and (iii) that findings bare little or no relevance for Critical Discourse Analysis (Wodak 2006). In this paper, I take up the first two of these positions and in doing so, of course, implicitly disagree with the third. I consider the positions in (i) and (ii), then, specifically in relation to Sperber's (2000, 2001) notion of a ‘logico-rhetorical' module. Taking the argument which Chilton makes concerning this module one stage further, I suggest that the logico-rhetorical module evolved as much for persuasion as it did for vigilance. I further suggest that the semantic category of evidentiality operationalised in media discourse is intended to satisfy the conditions of acceptance laid down by the logico-rhetorical module. I show how this semantic category therefore performs a legitimising function in media discourse on immigration.