To date, the only species to show compelling evidence of self-recognition are humans, chimpanzees, and orangutans. (Only one gorilla, Koko, has displayed self-recognition; see Patterson & Cohn, SAAH17). An important question is whether self-awareness is a uniquely primate (great ape–human) ability or a potential outcome of any sufficiently intelligent system. In order to address this question we can compare tests of self-awareness in primates with another taxonomic group that has diverged extensively from them yet displays a comparable level of neurobehavioral complexity, namely, the Cetacea. Comparisons of primates and cetaceans, therefore, form the basis for a test of convergent cognitive evolution and could set the stage for subsequent tests of the generality of Gallup's (1982) model of self-awareness.
Dolphins are provocative candidates for self-awareness for a number of reasons. They share those neurological, cognitive, and social characteristics with great apes and humans that are generally regarded as having been important for the development of self-awareness in primates. Humans, great apes, and dolphins show similarities across several measures of encephalization, including a high brain-weight / body-weight ratio (Glezer, Jacobs, & Morgane, 1988; Jerison, 1982), extensive cortical surface area (Jerison, 1982), and a high neocortical-volume / total-cortical-volume ratio (Glezer et al., 1988). The bottlenose dolphin is capable of high levels of performance on a variety of auditory learning, artificial language comprehension, and memory tasks comparable to those mastered by chimpanzees (for a review of this literature see Herman, 1986).