The study of ancient DNA has the potential to make significant and unique contributions to ecology and evolution. However, the techniques used contain inherent problems, particularly with regards to the generation of authentic and useful data. The solution currently advocated to reduce contamination and artefactual results is to adopt criteria for authentication. Nevertheless, these criteria are not foolproof, and we believe that they have, in practice, replaced the use of thought and prudence when designing and executing ancient DNA studies. We argue here that researchers in this field must take a more cognitive and self-critical approach. Specifically, in place of checking criteria off lists, researchers must explain, in sufficient enough detail to dispel doubt, how the data were obtained, and why they should be believed to be authentic.