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, 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 cellss, 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 difference between humans and their nearest cousins the chimpanzees (with whom we share 98% of our DNA) is that humans brain as compared to the Chimpanzee brain are 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. Chimpanzee brains by contrast are only 400g.
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]) 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 us 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 functionaity 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.
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, no study done on the brain waves of sleeping dolphins records the brain wave pattern associated with REM sleep. Unlike terrestial 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.)
We need a section on behaviour in the wild. See above for the difficulties in carrying out this kind of research. See also animal behaviour for a general discussion.
Should be a sub section of communication abilities
Should be a section on learning skills. Scientific tests relevant to:
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.
Scientific research into self-awareness has suggested that bottle-nosed dolphins possess self-awareness. Dolphins differ markedly so an assessment can not be made for all species, some of which have very much smaller brain size and presumably different structure.
The standard test for self-awareness in animals in the mirror recognition 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 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 Marten and Psarakos(1995) 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 we are little closer to definitive answers. We can say that average dolphin intelligence is somewhere on the continuum between above-average human and peak dog, but we cannot say definitively where.
See also: animal intelligence, Morgan's Canon
Differences from other Mammalian Brains
Behaviour
Communication
Learning and memory
Not only have dolphins exhibited to learn complex tricks, they have also demonstrated the ablility 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.Self-awareness
New Age claims
The intelligence of dolphins is the subject of much speculation and misinformation in popular culture. In particular, some adherents of New Age beliefs believe, for example, dolphins to be capable of perceiving higher dimensions of reality and being able to heal. These ideas probably originated with Dr John Lilly, with his books the Man and Dolphin and The Mind of the Dolphin. However, Lilly's ideas were not based on strict scientific studies, but rather anecdotal evidence, which remains unsupported. One must conclude that there is no reputable scientific evidence to back these types of claims.Conclusion
References and external links
Self awareness research
