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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.
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.
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 . 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 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 intpretated 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, 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 possible 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.
Should be a sub section of communication abilities
Should be a section on learning skills. Scientific tests relevant to:
Not only have dolphins exhibited the ability 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 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 animal intelligence, Morgan's Canon
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