The scientific and political communities must be aware of our bias in the knowledge of the taxonomy of the various living organisms. Although the effects of species concepts on conservation have received considerable attention, usage of the subspecies category in conservation lists have received insufficient scientific scrutiny, at least for most taxonomic groups and geographic regions. Here we draw from the class Mammalia to show that discrepancies in the inclusion of subspecies in the IUCN Red List often reflect uneven taxonomic knowledge and the differential scientific and public interest raised by different kinds of mammals, which together can produce a biased picture of mammalian endangerment worldwide.