  Gallup (1970) developed an experimental test of mirror self-recognition that has become widely used as a test of self-awareness, although interpretation of the test remains controversial (see the section on  self-consciousness and metacognition below). Gallup argues that the performance of chimpanzees in this test indicates that they are self-aware, and that animals that fail the test lack self-awareness. Further, foreshadowing Carruthers, Gallup argues that self-awareness — in the sense of being able to think about one's own mental states — is required for having a mind, and therefore that animals that ‘fail’ the mirror test have no minds (1982, 1985). Though there has been controversy over just which animals ‘pass’ the validity of versions of the test modified for use with elephants, dolphins,and magpies has been challenged  — as of 2002, Gallup maintained that there was evidence that humans, common chimpanzees, bonobos and orangutans consistently pass the test, and strong evidence that a wide range of other primates fail consistently fail. He took this to support the claim that self-awareness is unique to great apes (Gallup et al. 2002). Combined with his earlier arguments that consciousness requires the sort of self-awareness measured by the mirror test, this would imply that consciousness is unique to the great apes. 