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Cetaceans Have Complex Brains for Complex Cognition

  • Lori Marino mail,

    To whom correspondence should be addressed. E-mail: lmarino@emory.edu

    X
  • Richard C Connor,
  • R. Ewan Fordyce,
  • Louis M Herman,
  • Patrick R Hof,
  • Louis Lefebvre,
  • David Lusseau,
  • Brenda McCowan,
  • Esther A Nimchinsky,
  • Adam A Pack,
  • Luke Rendell,
  • Joy S Reidenberg,
  • Diana Reiss,
  • Mark D Uhen,
  • Estel Van der Gucht,
  • Hal Whitehead
  • Published: May 15, 2007
  • DOI: 10.1371/journal.pbio.0050139

Reader Comments (4)

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Conflicted Reasoning by Cetologists

Posted by plosbiology on 07 May 2009 at 22:18 GMT

Author: Paul Manger
Position: Reader
Institution: University of the Witwatersrand
E-mail: mangerpr@anatomy.wits.ac.za
Submitted Date: May 24, 2007
Published Date: May 25, 2007
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

The essay by Marino et al claims to advocate the theory of cetacean brains being large to subserve complex cognitive processes. It fails to substantiate the “intellectual” alternative over the thermogenetic proposal[1]. Whales have large brains (but small EQs), dolphins have relatively large brains (but small mass). Is it the large brain in absolute or relative terms making these brains cognitively complex? A link between increased relative brain size and sociality in cetaceans is claimed which is not correct ([1]Fig. 14). One author[2] has noted that hyena have more complex sociality than dolphins, yet hyenas don’t have a relatively large brain. Echolocation and brain size evolution has been addressed (pg 320[1]).

They claim ([21,22]) to use "modern neuroanatomical techniques", but use a method described in 1894[3]. This is used to discredit the anatomy I have based part of my ideas on, but the methods are identical. A recent study[4] using modern techniques shows identical results to earlier studies[5]. They accept there is no prefrontal cortex, but then claim an analogue located "somewhere" else. This contradicts all other mammals – do we ignore other mammals? They claim that the insular and cingulate cortex is analogous to that of primates. Unsubstantiated speculation. The function of spindle cells is not known in cetaceans. I proposed a function of glia in cetaceans based on their sleep[1]. Marino et al propose that glia are involved in cognitive processes. No one knows the function of the extra glia, but they claim to.

Televised learning apparently requires a big brain, yet chickens can[6]. Many animals (e.g goats) understand human pointing gestures[7]. Several previous studies failed the mirror test. ONLY the 2 dolphins studied by Reiss and Marino appear capable. If 2 dolphins can does it mean all cetaceans can? Dolphins mimic and synchrony is used as a marker of social alliance. Maybe the “mirror self-recognition” is social synchrony and not self-awareness? In the mirror test article the behavioural repertoire of the dolphins is not given even though they participate in shows. Are they mimicking show moves? The broad definition of culture means that many species, even octopus, have culture[8]. Teaching in Killer whales is restricted to ONE example. Do all cetaceans practice pedagogy? Sponge carrying has been seen in 25 dolphins. Do all cetaceans use tools? Marino et al claim the sponges are used to probe into crevices, but this is not from the original reports, the “sponging” dolphins forage on sandy sea bottoms. Is this a new observation (if so it should be indicated) or fabrication? Invertebrates use tools. This does not correlate with brain size.

The last sentence transcends the mystical, cetaceans being "rightfully oblivious" to my theory. Do the authors believe cetaceans heed their claims?

[1] Manger PR (2006) An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain. Biol Rev 81:293-338.
[2] Connor RC (2007) Complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals. Philos Trans Royal Soc B DOI: 10.1098/rstb.2006.
[3] Nissl F (1894) Ueber eine neue Untersuchungsmethode des Centralorgans zur Feststellung der Localisation der Nervenzellen. Neurologisches Centralblatt, Leipzig, 13:507-508.
[4] Fung C, Schleicher A, Kowalski T, Oelschlager HH (2005) Mapping auditory cortex in the La Plata dolphin (Pontoporia blainvillei). Brain Res Bull 66:353-356.
[5] Kesarev VS, Malofeyeva LI, Trykova OV (1977) Ecological specificity of cetacean neocortex. J Hirnforsch 18:447–460.
[6] Nicol C (2006) How animals learn from each other. App Anim Behav Sci 100:58-63.
[7] Miklosi A, Soprono K (2006) A comparative analysis of animals’ understanding of the human pointing gesture. Anim Cogn 9:81-93
[8] Janik VM (2001) Is cetacean social learning unique? Behav Brain Sci 24:337-338

No competing interests declared.