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

School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, Republic of South Africa. Electronic address: .
Neuroscience (Impact Factor: 3.36). 07/2013; 250. DOI: 10.1016/j.neuroscience.2013.07.041
Source: PubMed


This review evaluates and contextualizes the behavioural studies undertaken on cetaceans in terms of the relationship of these behaviours 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 behaviours 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 32 million years ago, at the Archaeocete - Neocete faunal transition, and have since remained stable in relative size. The behaviours 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 behaviours 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 behaviours in a broader comparative framework, and not the limited cetacean - great ape comparisons mostly used, it is evident that the behaviours 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.

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    • "Certain smaller cetaceans, of the suborder Odontoceti, are known to have brains that, relative to body mass, are the second largest to humans (Manger 2006). This observation, coupled with specific interpretations of cetacean behaviour (Manger 2013), provides the bases for the concept that cetaceans are cognitively complex (Marino et al. 2008). Thus, cetacean brains are thought to be able to generate behaviours that are beyond the cognitive capabilities present in the brains of most other mammals; however, it is clear that the cetacean brain has a morphology that is distinctly different from that of all other mammals (Glezer et al. 1988; Manger 2006; Manger et al. 2004, 2012) and thus the concept that cetaceans are cognitively complex has been questioned (Manger 2006, 2013) and vigorously defended (Marino et al. 2008). "
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    • "intelligence, with tests for mirror self-recognition (Reiss & Marino, 2001), language and symbolic comprehension (e.g., Herman et al. 1984, 1990, 1994, 2001), understanding of human pointing and head gaze (e.g., Pack & Herman, 2007), imitation and the cultural transmission of behavior (e.g., Deecke, Ford, & Spong, 2000), teaching (Guinet & Bouvier, 1995) and tool use (Krützen et al., 2005). Manger (2013) subjects all such studies to an extended critique, arguing that the evidence is either (a) inadequate to support such a claim for these skills as indicative of high-level cognitive skills, or (b) that such capacities are wide-spread in the animal kingdom, and hence cannot be used to account for any unique cetacean increase in cognitive capacity. No doubt these new claims will also be contested, but to continue the debate in this vein, we would argue, misses the point. "
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