Questioning the interpretations of behavioral observations of cetaceans: is there really support for a special intellectual status for this mammalian order?

This review evaluates and contextualizes the behavioral studies undertaken on cetaceans in terms of the relationship of these behaviors to special levels of intelligence associated with these marine mammals and the evolution of their relatively and absolutely large brain size. Many believe that the large size of the cetacean brain and reported behaviors indicate the need to create a special status for these animals in terms of their intellect, positing that they are second to humans in terms of general intelligence. Cetacean brains became relatively large approximately 32millionyearsago, at the Archaeocete-Neocete faunal transition, and have since remained stable in relative size. The behaviors reported for modern cetaceans are thought to parallel those of great apes, to the exclusion of other mammals. By creating an autocatalytic model of cetacean brain evolution, the behaviors thought to be indicative of sophisticated cognitive processes can be assessed as to their potential involvement in the evolution of larger brains in cetaceans. By contextualizing these behaviors in a broader comparative framework, and not the limited cetacean - great ape comparisons mostly used, it is evident that the behaviors used to argue for high levels of intelligence in cetaceans are found commonly across mammals and other vertebrates, and are often observed in invertebrates. This contextualization indicates that cetacean intelligence is qualitatively no different to other vertebrates. In addition, the inability of cetaceans to surpass Piaget stage 4/5 on object permanence tests and to solve an "if and only if, then" abstract task indicates the possibility that their levels of general intelligence may be less than that seen in other vertebrates. Sophisticated cognitive abilities appear to play no role in the evolution of large brain size in cetaceans, indicating that alternative theories of large brain size evolution in cetaceans should be considered in more detail.