Article

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: 3.33). 07/2013; 250. DOI: 10.1016/j.neuroscience.2013.07.041
Source: PubMed

ABSTRACT 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.

Download full-text

Full-text

Available from: Paul Manger, Sep 22, 2014
5 Followers
 · 
144 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Social Brain (or Social Intelligence) hypothesis is a very influential theory that ties brain size and, by extension, cognitive ability to the demands of obligate and intense sociality. Initially developed to explain primate brain size evolution, the Social Brain hypothesis has since been applied to a diverse array of other social taxa, both mammalian and avian; its origins as a primate-based hypothesis (especially as articulated by Humphrey, 1976), however, mean that it retains a heavily anthropocentric tinge. This colors the way in which other species are viewed, and their cognitive abilities tested, despite fundamental differences in many aspects of bodily morphology, brain anatomy and behavior. The delphinids are a case in point and, in this review, we demonstrate how the anthropocentric origins of the Social Brain hypothesis have pushed us toward a view of the delphinids as a species of ̳aquatic ape‘. We suggest that a more ecological, embodied/embedded, view of dolphin behavior and psychology undercuts such a view, and will provide a more satisfactory assessment of the natural intelligence the delphinids display.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The hippocampus is essential for the formation and retrieval of memories and is a crucial neural structure sub-serving complex cognition. Adult hippocampal neurogenesis, the birth, migration and integration of new neurons, is thought to contribute to hippocampal circuit plasticity to augment function. We evaluated hippocampal volume in relation to brain volume in 375 mammal species and examined 71 mammal species for the presence of adult hippocampal neurogenesis using immunohistochemistry for doublecortin, an endogenous marker of immature neurons that can be used as a proxy marker for the presence of adult neurogenesis. We identified that the hippocampus in cetaceans (whales, dolphins and porpoises) is both absolutely and relatively small for their overall brain size, and found that the mammalian hippocampus scaled as an exponential function in relation to brain volume. In contrast, the amygdala was found to scale as a linear function of brain volume, but again, the relative size of the amygdala in cetaceans was small. The cetacean hippocampus lacks staining for doublecortin in the dentate gyrus and thus shows no clear signs of adult hippocampal neurogenesis. This lack of evidence of adult hippocampal neurogenesis, along with the small hippocampus, questions current assumptions regarding cognitive abilities associated with hippocampal function in the cetaceans. These anatomical features of the cetacean hippocampus may be related to the lack of postnatal sleep, causing a postnatal cessation of hippocampal neurogenesis.
    Brain Structure and Function 11/2013; 220(1). DOI:10.1007/s00429-013-0660-1 · 4.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The ability to process visual information using relational rules allows for decisions independent of the specific physical attributes of individual stimuli. Until recently, the manipulation of relational concepts was considered as a prerogative of large mammalian brains. Here we show that individual free flying honeybees can learn to use size relationship rules to choose either the larger or smaller stimulus as the correct solution in a given context, and subsequently apply the learnt rule to novel colors and shapes providing that there is sufficient input to the long wavelength (green) photoreceptor channel. Our results add a novel, size-based conceptual rule to the set of relational concepts that honeybees have been shown to master and underline the value of bees as an animal model for studying the emergence of conceptualization abilities.
    Frontiers in Behavioral Neuroscience 03/2014; 8:80. DOI:10.3389/fnbeh.2014.00080 · 4.16 Impact Factor