Cetacean intelligence

Knowledge about cognitive capabilities of the dolphin brain (and its related issue: the nature and magnitude of dolphin intelligence) is still limited. This article addresses some of the verifiable facts about the dolphin brain. It should be noted that there are many different species of dolphin (see the cetacea article for a full list), and so one should be careful about generalisations, because differences between dolphin species may be as marked as differences between humans and the great apes.


Research difficulties

Knowledge about the capabilities of the dolphin brain is limited because of major research difficulties. Research of cetacean behaviour in the wild is among the most expensive and difficult to carry out, owing to the nature of the environment they inhabit. There have therefore been relatively few scientific studies of dolphins in the wild, and most direct observations are anecdotal. Studies based on captive dolphins have limits, because it is not clear how natural their behaviour is under those conditions.

In addition, the United States Navy has allegedly carried out a substantial amount of research which has not been put in the public domain. The US Navy does acknowledge that its dolphin programme has trained dolphins to search and tag mines and warn of divers approaching installations. Rumours circulate about less benign uses, but these are unsubstantiated.

Brain Size and Mass

Some attempts to resolve the issue of dolphin intelligence have focused on various indicators concerning the size of the dolphin's brain. The relationship between brain mass and intelligence is a shaky one, at best. Cognitive ability, according to most scientists, is dependent on the quantity and quality of connections between brain cells, and not on mere brain mass. But if dolphins were equipped with brains notably smaller than those of humans, it would make a powerful case against their having intelligence that approached that of humans (a certain amount of mass is necessary, after all, to allow for sufficient neural connections to be made). One of the major differences between humans and their nearest cousins the chimpanzees is that the human brain as compared to the chimpanzee brain is much larger in size, size proportionate to body, and proportionate size at birth.

Most dolphin species have brains that are roughly equal in weight to the average human brain: for example, the average human brain weighs 1300-1400 grams, while the average bottle-nosed dolphin (Tursiops truncatus) brain weighs 1500-1600 grams, according to A. Berta's book Marine Mammals, quoted at this site (http://faculty.washington.edu/chudler/facts.html). Chimpanzee brains by contrast are only 400 grams.

However, many researchers believe that brain mass of itself is a poor measure because it makes no allowances for body size. Negative evidence against dolphins being as intelligent as humans is the fact that the dolphin brain to body ratio is less than half that (Klinowska, Margaret (1994), quoted at (2) (http://dubinserver.colorado.edu/prj/jbes03/brain.html)) of humans on average. However, it is not clear that direct comparisons of species that occupy such different habitats is appropriate, given these differing habitats make hugely different demands on bodily functionality. For instance, cetaceans have a high percentage of body weight in blubber, which principally helps them deal with the effects of water temperature. In the case of bottle-nosed dolphins blubber takes up 18-20% of body weight.

Other researchers have asserted that an important measure is the size and complexity of brain at birth. This is an extremely positive indicator for dolphin intelligence. Bottle-nosed dolphins begin life with very large brains: at birth they have a brain mass that is 42.5% of an adult human's brain mass (in comparison with humans, who at birth have 25% of adult brain mass). By eighteen months, the brain mass of Bottle-nosed dolphins is roughly 80% of that of an adult human. Human beings generally do not achieve this figure until the age of three or four.

The true value of various comparisons of brain mass between dolphins and human is debatable. Comparisons of humans to closely related species like the Great Apes would seem appropriate, since our original habitats and thus bodily functionality are very similar. However, one needs to be careful of directly comparing a land based species and water based species, because their habitats make hugely differing demands. It should be noted, however, that no other species seems to compare so favourably with humans across the indicators of pure brain mass, brain to body ratio, and comparative percentage of size at birth.

Differences from other mammalian brains

Although dolphins are themselves mammals, their brains are constructed and act differently than those of most mammals. Unlike most mammalian brains, which have six neocortical layers, dolphins have five. While most sleeping mammals go through a stage known as REM sleep, dolphin studies have not shown any brain wave patterns associated with REM sleep. Unlike terrestrial mammals, dolphin brains contain a paralimbic lobe, which may possibly be used for sensory processing.

Dolphin brain stem transmission time is faster than that normally found in humans, and is roughly equivalent to the speed found in rats. As echo-location is the dolphin's primary means of sensing its environment -- analogous to eyes in primates -- and since sound travels four and a half times faster in water than in air, scientists speculate that the faster brain stem transmission time, and perhaps the paralimbic lobe as well, support speedy processing of sound. The dolphin's dependence on speedy sound processing is evident in the structure of its brain: its neural area devoted to visual imaging is only about one-tenth that of the human brain, while the area devoted to acoustical imaging is about 10 times that of the human brain. (Which is unsurprising: primate brains devote far more volume to visual processing than almost any other animals, and human brains more than other primates.)


See also animal behaviour for a broader view.

Researching the behaviour of dolphins in the wild is a difficult task. However several researchers have examined the social behaviour of dolphins and tried to extract from an understanding of the level of communication between individuals, which in turn is interpreted as a measure of intelligence.

Dolphin groups sizes vary quite dramatically. Older male Orca tend to lead quite solitary lives but this is the exception. River dolphins usually congregate in fairly small groups, from 6 to 12 in number. Researchers expect that the individuals in these small groups may well know and recognise each other. Other species such as the oceanic Pantropical Spotted Dolphin, Heaviside's Dolphin and Spinner Dolphin travel in vast crowds, sometimes thousands in number. It is extremely unlikely that every member of the group is acquitanted with every other, as this would require more social interaction than found in humans. However there is no doubt that such large packs can act as a single cohesive unit - observations show that if an unexpected disturbance such as a shark approach from the flank or from beneath the group occurs, the group moves in near unison to avoid the threat. This means that the dolphins must not only be aware of their next-door neighbours but also other individuals near by - in a similar manner to which humans perform "Mexican waves". This is achieved by sight, and possibly also echolocation. One controversial theory proposed by Jerison (1986) is that the pack of dolphins are able to share echolocation results between each other to create a better understanding of their surroundings. In the Encyclopedia of Marine Mammals Bernd Wersig compares this to a group of humans being able to share exactly what they can see with each other and so create a better 3D visual representation for all. Jerison goes to speculate that these "shared data" echolocation maps might account for the relatively large dolphin brain discussed above. This idea has not received much formal backing in the literature.

Complex play

Dolphins are known to engage in complex play behavior which includes such things as producing stable underwater toroidal air core vortex rings or "bubble rings"[1] (http://www.deepocean.net/deepocean/index.php?science09.php). The two main methods of bubble ring production are rapid puffing of a burst of air into the water and allowing it to rise to the surface, forming a ring and the other is performed by the dolphin swimming repeatedly in a circle and then stopping to inject air in to the helical vortex currents thus formed. The dolphin will often then examine its creation visually and with sonar. They also appear to enjoy biting the vortex-rings they've created so that they burst into many separate normal bubbles and then rise quickly to the surface. [2] (http://www.bubblerings.com/bubblerings/videos/) Certain whales are also known to produce bubble rings.


Should be a sub section of communication abilities

  • sign language
  • echolocation
  • body language
  • some studies have made wild claims.
  • need to criticise methodology as well.

Cetaceans communicate by using echolocation. Echolocation was discovered by Donald Griffin in 1944. For more information on cetacean echolocation see Animal echolocation or visit this website: http://members.fortunecity.com/anemaw/ultrasonic.htm

Learning and memory

Should be a section on learning skills. Scientific tests relevant to:

  • Learning tricks - dolphins have been taught extremely complicated tricks.
  • Lying and subterfuge - there are some studies which suggest ability to use subterfuge. Dolphin training the trainer suggestions
  • Learning to learn - there was a study on the ability to learn that a variable response was required to get a reward. Did similar study on humans and compared.
  • Long and short term memory
  • Ability to abstract
  • Need to criticise the methodology of these studies

Not only have dolphins exhibited the ability to learn complex tricks, they have also demonstrated the ability to produce creative responses. This was studied by Karen Pryor in the mid-sixties at Sea Life Park in Hawaii, and was published as "The Creative Porpoise: Training for Novel Behavior" in 1969. The two test subjects were two rough-toothed dolphins (Steno bredanensis), called Malia (a regular show performer at Sea Life Park) and Hou (a research subject at adjacent Oceanic Institute). The experiment tested when and whether the dolphins would identify that they were being rewarded (by fish) for originality in behaviour. So the trainer would reward the dolphin for a novel behaviour, but would not if the same behaviour was repeated. The experiment was highly successful. Malia finally learnt what was expected after a few days and from the fifteenth session produced an original behaviour to get a reward. Hou took thirty three sessions to reach the same stage. On each occasion the experiment was stopped when the variability of dolphin behaviour became too complex to make further positive reinforcing meaningful.

However, though this impressed researchers at the time, experiments by Neuringer(1992) and others have shown that other animals like pigeons and rats can likewise be trained for variability of response, which given time can result in apparently original behaviour. Whether there is a clear case for dolphins showing real creativity in this experiment is therefore questionable. Arguably the quality of the dolphins' response was far superior, but further research is required in this area to test this.


The ability to possess self-awareness shows a highly developed abstract thinking. Self-awareness is the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Scientific research into self-awareness has suggested that Bottlenose Dolphins possess self-awareness. Dolphins differ markedly so an assessment can not be made for all species, some of which have much smaller brain sizes and presumably different structures.

The standard test for self-awareness in animals is the mirror test, developed by Gallup in the seventies, in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror. Most animals react to a mirror as if it is another animal. However, like great apes, dolphins have been shown to recognise the mirror image as themselves, by examining the marking on their body. Evidence for mirror recognition by dolphins was anecdotal until the nineties, but the scientific studies carried out by researchers Marten and Psarakos (1994, 1995) and Reiss and Marino (1998) confirmed it.

Some scientists still disagree with these findings arguing that the results of these tests are open to human interpretation. This test is far less definitive than when used for primates because primates can touch the mark or the mirror, while dolphins cannot, making their alleged self-recognition behaviour less clear. Critics argue that behaviours that are said to identify self-awareness resemble existing social behaviours, and so researchers could be mislabelling social responses to another dolphin. The researchers counterargue that the behaviours shown to evidence self awareness are very different to normal responses to another dolphin, including paying significantly more attention to another dolphin than towards their mirror image. Dr. Gallup called the results "the most suggestive evidence to date" of mirror self-recognition in dolphins, but "not definitive" because he was not entirely clear that the dolphins were not interpreting the image in the mirror as another animal.

As a further response to these criticisms, in 1995, Marten and Psarakos used television to test dolphin self awareness. They showed dolphins real time footage of themselves, recorded footage and another dolphin. They concluded that their evidence suggested self-awareness rather than social behaviour. This study has not been repeated since then however, so the results remain unverified.


It is difficult to establish the level of intelligence in dolphins, not least because it is difficult to decide on an appropriate criteria for intelligence. Are homocentric standards of intelligence suitable for water-based dolphin species? Despite scientific study for over forty years, scientists are little closer to definitive answers. We can certainly say that dolphins are at least as intelligent as canines. But does their thinking approximate that of humans -- and if so, in what ways? Today's research provides tantalizing clues pointing to significant intelligence, but few final answers.

See also: animal intelligence, Morgan's Canon

References and external links

  1. Brain facts and figures (http://faculty.washington.edu/chudler/facts.html).
  2. The dolphin brain (http://dubinserver.colorado.edu/prj/jbes03/brain.html) a scholarly page at the University of Colorado, Boulder.
  3. The Dolphin Brain Atlas (http://www.msu.edu/user/brains/turs/) A collection of stained brain sections and MRI images.
  4. Bottle-nose dolphin brain (http://brainmuseum.org/Specimens/cetacea/dolphin/) from the comparative mammalian brain collection.
  5. Dolphin brains (http://www.sciencenetlinks.com/sci_update.cfm?DocID=76), an AAAS Science Netlinks feature.
  6. Deep thinkers (http://www.guardian.co.uk/life/feature/story/0,13026,989714,00.html) Article from the Guardian about dolphin intelligence
  7. Google group post on theories of dolphin brain size (http://groups.google.co.uk/groups?q=dolphin+intelligence&hl=en&lr=lang_en&ie=UTF-8&oe=UTF-8&selm=19980119233800.SAA22009%40ladder02.news.aol.com&rnum=6) by "draygon@aol.com", a junior level biology (zoology) student at the University of Texas at El Paso Will be useful for article
  8. BAYWATCH.(bottlenose dolphins research) (http://www.findarticles.com/cf_dls/m1511/3_21/59535404/p1/article.jhtml?term) Article on research into dolphins at Sarasota Bay
  9. Memory for recent actions in the bottlenoseddolphin (Tursiops truncatus): Repetition of arbitrary behaviors using an abstract rule (http://www.acsu.buffalo.edu/~emiii/alb.pdf) Research study examining ability of dolphins to remember, learn and abstract.
  10. Prologue to encounters with Whales and Dolphins (http://www.wadedoak.com/projectinterlock.htm) Interesting article mainly on research difficulties with whales and dolphins
  11. Dolphin Intelligence and the Captivity Issue (http://whales7.tripod.com/policies/levasseur/) Series of articles by Kenneth W. LeVasseur. Written scientifically, provide bibiliography, but no official standing given. Interesting points on early research into dolphins.
  12. Modern Reinforcement-Related Learning Theories (http://clawww.lmu.edu/faculty/lswenson/Learning511/L10REIN.html) Summary of research
  13. Brains, Behaviour and Intelligence in Cetaceans (Whales, Dolphins and Porpoises) (http://www.highnorth.no/Library/Myths/br-be-an.htm) Research paper by Margaret Klinowska of Cambridge University
  14. Towards Communication with Dolphins (http://www-2.cs.cmu.edu/%7Etanja/Dolphins/index.html) Project using computer software to try to understand dolphin communication

Self awareness research

  1. Evidence of self-awareness in the bottlenose dolphin (http://planet-hawaii.com/earthtrust/delbook.html) Academic study on dolphin self awareness by Marten and Psarakos(1994)
  2. Using Self-View Television to Distinguish between Self-Examination and Social Behavior in the Bottlenose Dolphin (Tursiops truncatus) (http://www.earthtrust.org/delart.html) Another study by Marten and Psarakos on self reflection using TV (1995)
  3. Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence (http://www.pnas.org/cgi/reprint/98/10/5937.pdf) Academic study on self awareness by Reiss and Marino (1998)
  4. Hey, That's Me! Measuring a Dolphin's Intelligence with a Mirror (http://www.pulseplanet.com/feat_archive/Oct01/) Popularized article on Reiss and Marino study on self awareness.
  5. Dolphin Self-Recognition Mirrors Our Own (http://www.sciam.com/article.cfm?articleID=0002433B-A643-1C5E-B882809EC588ED9F) Another article on Reiss and Marino study
  6. Research suggests dolphins capable of self-recognition  (http://www.jhu.edu/~newslett/05-3-01/Science/2.html) Article on two studies on self recognition in dolphins

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