A new ancient DNA study published in PLoS One is the first to demonstrate that disease can cause extinction in mammals, supporting the “hyperdisease” hypothesis. This study found rat-specific trypanosomes in museum specimens of native Christmas Island rats collected after but not before contact with black rats. It is assumed that black rats brought the pathogen to these immunologically naïve species; both Rattus macleari and R. nativitatis went extinct within a decade, by 1908.