which may explain their failure to touch a mark on their heads in the mirror test. Frans de Waal, a biologist and primatologist at Emory University, has stated that self-awareness is not binary, and the mirror test should not be relied upon as a sole indicator of self-awareness, though it is a good test to have. Different animals adapt to the mirror in different ways. Finally, controversy arose over whether self-recognition (through specifically visual stimuli) implies self-awareness. Dogs recognize their own scent as different from others' scents, but fail the traditional, visual mirror test. There are also many animals that are biologically unfit for this test, for example, certain species of mole that are born blind. Non-human animals Several studies using a wide range of species have investigated the occurrence of spontaneous, mark-directed behavior when given a mirror, as originally proposed by Gallup. Most marked animals given a mirror initially respond with social behavior, such as aggressive displays, and continue to do so during repeated testing. Only a few species have touched or directed behavior toward the mark, thereby passing the classic MSR test. Findings in MSR studies are not always conclusive. Even in chimpanzees, the species most studied and with the most convincing findings, clear-cut evidence of self-recognition is not obtained in all individuals tested. Prevalence is about 75% in young adults and considerably less in young and aging individuals. Until the 2008 study on magpies, self-recognition was thought to reside in the neocortex area of the brain. However, this brain region is absent in nonmammals. Self-recognition may be a case of convergent evolution, where similar evolutionary pressures result in similar behaviors or traits, although species arrive at them by different routes, and the underlying mechanism may be different. Animals that have passed Mammals Cetaceans Bottlenose dolphin (Tursiops truncatus): Researchers in a study on two male bottlenose dolphins observed their reactions to mirrors after having a mark placed on them. Reactions such as decreased delay in approaching the mirror, repetitious head circling and close viewing of the eye or genital region that had been marked, were reported as evidence of MSR in these species. Killer whale (Orcinus orca): Killer whales and false killer whales (Pseudorca crassidens) may be able to recognise themselves in mirrors. Primates Bonobo (Pan paniscus) Bornean orangutan (Pongo pygmaeus): However, mirror tests with an infant (2-year-old), male orangutan failed to reveal self-recognition. Chimpanzee (Pan troglodytes): However,