Why Question the Idea of Dolphin Intelligence? – Professor Paul Manger

A recently aired documentary on Eden TV highlighted some of my scientific research1 into the concept of intelligence in whales and dolphins, and provided what many think is an iconoclastic view, as I posit that these animals are nowhere near as intelligent as is commonly believed.

Why is it commonly thought that whales and dolphins are the second most intelligent animals on the planet (after us of course)? From a scientific viewpoint, the size of the brain (both in absolute size and in size relative to the body)2 and certain behaviours (such as vocalizations, etc.)3 provide the basis for the conclusions, often going far beyond what the data implies, reached by several researchers. These observations have led to the almost universal tenet that whales and dolphins are very intelligent and that we should spend a great deal of our resources protecting them from the destruction humans have wreaked upon the planet4.

So why is my view at odds with this more standard view? My interest in this topic was first piqued by Prof. Kira Nikolskaya of the University of Moscow, when one of her previous students (Dr. Oxana Yeschenko) told me about the behavioural studies Prof. Nikolskaya had done that showed dolphins incapable of solving a complex problem – one that even goldfish could solve (given enough time)!5 The mystery here was why did dolphins fail this task? Kira asked me to look into the structure of the dolphin and whale brain to see if I could find something to explain her results, and this took me on a five-year journey of discovery and led to a novel idea regarding the evolution of a large brain in the whales and dolphins.

In retrospect I can now order my thoughts in a way that makes all this work relatively easy to understand. The first point that needs to be made is that even though the brains of humans and cetaceans are both large and large relative to body size, it doesn’t mean that they undertake the same function. A good analogy for this is the human hand. It is small, but manually dextrous. The flipper of a blue whale is very large – but does this make it more manually dextrous that the human hand? The simple answer is no, the reason being it is not built the same as the human hand – there is no opposable thumb.

The same reasoning applies to the brain. The brains of cetaceans are not organized in the same way as human brains. There are many features of the human brain, ones that are known to underlie our cognitive abilities, that are different or absent in the cetacean brain. A few examples include the lack of a prefrontal lobe in cetaceans, the region of the human brain that processes our most complex cognitive mentations. A second example is the small size of the hippocampal formation in cetaceans, this being the area of the brain involved in memory formation and recall and also in navigation.

The neurons of the cetacean brain are also quite simple in their morphology in comparison to human brains, but perhaps most importantly, there is an inordinately high number of glial cells in the cetacean brain in comparison to all other mammals. Glial cells are not directly involved in information processing, but are involved in creating the environment for neurons to function correctly – one important function being the production of heat.

Given that the cetacean brain is built differently to human (and indeed all other mammal) brains, why do they have such a large brain? A combination of the microstructure of the brain, the way in which cetaceans sleep (with half the brain at a time)6 and the evolutionary history of cetaceans, provided me with a novel hypothesis – that cetacean brains are large in order to overcome the rate of heat loss to the water.

Heat is lost to water at a rate 90 times faster than it is to air, therefore this is a significant environmental pressure faced by cetaceans. Interestingly, the size of the cetacean brain became large at a period in the earth’s history (about 32 million years ago) when the water temperatures dropped dramatically. The distribution of modern whale and dolphin species also appears to be tightly linked to water temperature, as does their relative brain size. The clear conclusion is that cetacean brains evolved their size in response to the selection pressure of water temperature – lots of extra glia to provide heat for a small number of neurons.

This hypothesis has met with a great deal of criticism, mostly from those with a vested interest (either scientifically7 or financially8) in maintaining the idea of cetacean intelligence. Some have even accused the hypothesis I have forwarded as a catalyst for the destruction of the remaining populations of cetaceans across the globe!9

My view is again completely different to this. If we wish to understand a particular problem, the more accurate information we have at our disposal, the better decisions we can make. As humans we do make decisions about the management of other species and how our activities affect them. If cetaceans are really not what many people believe them to be, then we can make better-informed decisions about their management, both in the long and short term. If, alternatively, we attempt to make decisions without the correct information, we will undoubtedly make bad decisions.

The work I have done has led to a novel way of thinking regarding cetaceans, and as a scientific hypothesis it is open to further exploration. At this stage, while there is a great deal of evidence supporting the hypothesis I have forwarded, there is still a great deal of opposition to this idea. It is only with further work, leading to either support or refutation of either side of the debate that we will arrive at a better understanding of cetaceans. Even if my hypothesis turns out to be incorrect, it will have stimulated the search for truth in a more rigorous manner, and undoubtedly, the information gained through this debate can only be beneficial to our understanding of cetaceans and how our actions may affect these species.


(1) Manger P. An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain. Biol Rev Camb Philos Soc. 81: 293-338 (2006)
(2) Marino L, Butti C, Connor R, Fordyce R, Herman L, Hof P, Lefebvre L, Lusseau D, McCowan B, Nimchimsky E, Pack A, Reidenberg J, Reiss D, Rendell L, Uhen M, Van der Gucht E, Whitehead H. A claim in search of evidence: reply to Manger’s thermogenesis hypothesis of cetacean brain structure. Biol Rev Camb Philos Soc. 83: 417-440 (2008)
(3) Simmonds M. Into the brains of whales. App Anim Behav Sci. 100:103-116 (2006)
(4) http://cetaceanconservation.com.au/cetaceanrights/
(5) Nikolskaya K. Evolutionary aspects of intellect in vertebrates: can intellect be a factor confining choice of the habitat? http://zhurnal.ape.relarn.ru/articles/2005/143.pdf
(6) Lyamin O, Manger P, Ridgway S, Mukhametov L, Siegel J. Cetacean sleep: an unusual form of mammalian sleep. Neurosci Biobehav Rev 32: 1451-1484 (2008)
(7) Grimm D. Are dolphins too smart for captivity? Science 332: 526-529 (2011)
(8) http://www.seashepherd.org/news-and-media/editorial-060821-1.html
(9) Letter from a South African cetacean activist addressed to Deputy Vice-Chancellor for Research of the University of the Witwatersrand demanding that my employment be terminated (2006)

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