The present study examined whether English and Indonesian naming practices are predictive of children’s and adults’ conceptions of animal, specifically, the hierarchical relationships between human, mammal and animal. At age 6, English speakers were almost two times more likely than Indonesian speakers to agree that mammals are animals. At age 9, English speakers were three times more likely than Indonesian speakers to agree that humans are mammals. As adults, Indonesian (but not English) speakers continued to deny that humans are animals. That is, the Indonesian naming practice that leads speakers to deny that humans are animals appears related to a delay in Indonesian-speaking children’s acceptance that mammals are animals and humans are mammals. We conclude that this delay may stem from a conflict between categorical knowledge and well-established naming practices.