Cetacean intelligence

From Freepedia

Cetacean intelligence denotes the cognitive capabilities of the cetacean order of mammals and most especially the various species of dolphin. Cetaceans include whales, porpoises and dolphins and while all are broadly considered intelligent, dolphins have generated the most attention as their capabilities appear to be of a different order than that of their relatives.

Conclusions about the nature and magnitude of dolphin intelligence have not yet been reached. There are many different species of dolphin (see the cetacea article for a full list) and generalisations can be easily mis-applied; cognitive differences between dolphin species may be as marked as differences between humans and the great apes.

Contents

Research difficulties

Knowledge about the capabilities of the dolphin brain is limited because of major research difficulties. Research of cetacean behavior 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 U.S. Navy does acknowledge that its dolphin program 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 Characteristics

While there is no physiological characteristic that unequivocally indicates intelligence in animals, scientists naturally focus on brain size and structure. Absolute brain size does appear to correlate to intelligence[1] but it is a crude measure given that animal species vary in size over many orders of magnitude. Brain-to-body ratio is considered a more precise benchmark, particularly for species that are otherwise similar in size (the larger the species the smaller the brain-to-body mass ratios as a general rule). Comparing a land based species and water based species introduces a further complication because their habitats make hugely differing demands. Even accepting these caveats, dolphin brain characteristics appear positive indicators of advanced intelligence.

  • Bottle-nosed dolphins (Tursiops truncatus) have an absolute brain mass of 1500-1700 grams. This is slightly greater than that of humans (1300-1400 grams) and about four times that of chimps (400 grams) [2].
  • The brain-to-body ratio in dolphins is less than half that of humans: 0.9% versus 2.1%.[3] This comparison appears more favourable if we leave aside the large amount of blubber (15-20% of mass) dolphins require for insulation. Humans and dolphins are one and two, respectively, for animal brain-to-body ratio, among all animals weighing more than one kilogram.
  • At birth, dolphins have a brain mass that is 42.5% of an adult dolphin's brain mass (in comparison with 25% for human newborns). By eighteen months, the brain mass of Bottle-nosed dolphins is roughly 80% of that of an adult dolphin. Human beings generally do not achieve this figure until the age of three or four (ibid).

Turning to brain structure and the complexity of neural connections, dolphins continue to compare favourably to humans.

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.)

Behavior

See also animal behavior for a broader view.

Researching the behavior of dolphins in the wild is a difficult task. However, several researchers have examined the social behavior 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.

Pack characteristics

Dolphin group 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 acquainted 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 hypothesis 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"[5]. 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. [6] Certain whales are also known to produce bubble rings.

Creative behavior

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.


Communication

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

It has been suggested that dolphins might be able to communicate with each other by reproducing the sounds echoed by objects targeted by echolocation. This would mean, essentially, that dolphins can show "acoustic images" to other dolphins.

However, this is one of many unsubstantiated hypotheses that have been made about dolphin communication. Unfortunately, the environment where dolphins live makes experiments much more expensive and complicated than for other species; additionally, the fact that cetaceans can emit and hear sounds (which are believed to be their main means of communication) in a range of frequencies much bigger than humans' means that sophisticated equipment, which was scarcely available in the past, is needed to record and analyse them.

Among the few estabilished facts is that dolphins emit two very distinct kinds of acoustic signals, which we call whistles and clicks. Clicks - quick bursts of very short pulses - are used for echolocations, although it cannot be excluded that they serve communication purposes, as well. Pulses in a click train are usually spaced a few tens of milliseconds, and each pulse may last for fractions of a millisecond. The function of whistles is largely unknown, although it is widely assumed that they must carry some more or less advanced form of communication.

There is strong evidence that some specific whistles, called signature whistles, are used by dolphins to identify and/or call each other; dolphins have been observed emitting both other specimens' signature whistles, and their own. A unique signature whistle develops quite early in a dolphin's life, and it appears to be created in an imitation of the signature whistle of the dolphin's mother.

Signature whistles, however, form only a small percentage of a dolphin's vocalizations; the significance of the rest (apart from things like simple, stereotyped distress or help calls) remains largely unknown. A paper by scientists Vladimir I. Markov and Vera M. Ostrovskaya, an abstract of which can be read [on this site], reports evidence of an extremely complex structure of dolphin vocalizations; while the study does not claim the presence of a language comparable to those of humans, the apparent existence of a framework developed enough to support such a language is certainly very intriguing.

Self-awareness

The ability to possess self-awareness shows 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 1990's when 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.

See also

References and external links

  1. Brain facts and figures.
  2. The dolphin brain a scholarly page at the University of Colorado, Boulder.
  3. The Dolphin Brain Atlas A collection of stained brain sections and MRI images.
  4. Bottle-nose dolphin brain from the comparative mammalian brain collection.
  5. Dolphin brains, an AAAS Science Netlinks feature.
  6. Deep thinkers Article from the Guardian about dolphin intelligence
  7. Google group post on theories of dolphin brain size 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) 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 Research study examining ability of dolphins to remember, learn and abstract.
  10. Prologue to encounters with Whales and Dolphins Interesting article mainly on research difficulties with whales and dolphins
  11. Dolphin Intelligence and the Captivity Issue 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 Summary of research
  13. Brains, Behaviour and Intelligence in Cetaceans (Whales, Dolphins and Porpoises) Research paper by Margaret Klinowska of Cambridge University
  14. Towards Communication with Dolphins Project using computer software to try to understand dolphin communication
  15. Learned behaviour in Killer Whales

Self awareness research

  1. Evidence of self-awareness in the bottlenose dolphin 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) 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 Academic study on self awareness by Reiss and Marino (1998)
  4. Hey, That's Me! Measuring a Dolphin's Intelligence with a Mirror Popularized article on Reiss and Marino study on self awareness.
  5. Dolphin Self-Recognition Mirrors Our Own Another article on Reiss and Marino study
  6. Research suggests dolphins capable of self-recognition Article on two studies on self recognition in dolphins
Retrieved from "http://en.freepedia.org/Cetacean_intelligence.html"


Views
Personal tools
Similar Links