User:Jwrosenzweig/Dolphin intelligence

The magnitude of dolphin intelligence has long been under investigation by scientists, who hope to better understand cognition in general by understanding the workings of the dolphin brain. Answers to the question "how intelligent are dolphins" range widely, from those suggesting that dolphins are, in many ways, superior to humans in their mental abilities to those portraying dolphins as merely highly sophisticated animals whose cognitive abilities cannot truly be called "intelligence". The issues raised by the question of dolphin intelligence are many: the central areas of discussion are noted below.

Brain Size and Mass

Some attempts to resolve the issue of dolphin intelligence have focused on the size of the dolphin's brain (both its weight and its size relative to its body). 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. 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).

However, 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. Another positive indicator for dolphin intelligence is that they begin life with very large brains, proportionally: by the time a dolphin is eighteen months old, its brain mass is roughly 80% of that of an adult human. Human beings generally do not achieve this figure until the age of three or four.

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, 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 or cats, and is roughly equivalent to the speed found in rats. This is also a possible indicator of intelligence, but not a conclusive sign of it: rat intelligence, after all, is not thought to be equivalent to that of dolphins. 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.

Consciousness or Self-Awareness

One standard test for self-awareness in animals is the mirror recognition test. Some accounts claim that dolphins recognize themselves in mirrors (or mirror analogues, such as video screens); these studies are disputed by other scientists for a number of technical reasons (ability of dolphins to recognize stimuli via other sensory modalities, etc.).

The intelligence of dolphins is the subject of much speculation. In particular, some adherents of New Age beliefs believe them to be capable of perceiving higher dimensions of reality. There is no scientific evidence whatsoever to back these claims.

Speculative claims and unconfirmed information

According to Carol J. Howard, author of Dolphin Chronicles (1996), each of the two dolphin sub-brains has an independent blood supply. The two eyes of the dolphin are each connected to one of the two sub-brains.

It is possible that, if they have two brains, dolphins never sleep with both brains at once. One brain sleeps while the other brain stays awake (perhaps so that the dolphins can breathe while asleep): this may account for the lack of REM sleep brain waves among dolphins.

It has been long theorised that dolphins have a complex language, which may consist of visual symbols as interpretations of high frequency sound waves (see synaesthesia). Many scientists feel there is too little evidence for this claim, although some believe it is justified.

References and external links

1. Brain facts and figures.
2. The dolphin brain a scholarly page at the University of Colorado, Boulder, and the source of much of the information posted above regarding dolphin brain mass and design.
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.