This paper examines the problem of Ptolemaic incest from a variety of cross-disciplinary perspectives. Specifically, it seeks to establish the following: that there is little in the ancient record to support the common claim that the Ptolemies suffered extensively from the deleterious genetic effects of inbreeding; that the various theories so far put forward as explanations for Ptolemaic incest offer at best only a partial rationale for this dynastic practice; that the most compelling rationale for Ptolemaic incest is to be found in complex, and perhaps unconscious, symbolic motivations analogous to those observed by anthropologists in other cultures; and finally, that, for the Ptolemies, incest was, like the "truphê" for which they were so notorious, a dynastic signature which highlighted their singularity and above all, their power.