Dolphins have a brain, which in proportion to their body size is one of the largest in the animal kingdom and is twice the size of the chimpanzee. This brain mass to body mass ratio is normally a better indicator of brain power than just brain size alone. They have a playful nature and a reputation for being intelligent. Dolphins have colonised the worlds oceans from the icy waters of the poles to the warm waters of the tropics. They are highly social - like us - and live in complex societies. They can learn complicated tasks, they can understand and copy human signals. But are these just clever tricks that they learn or do they think about what they are doing ? One way to answer that question is to measure dolphins ability on various mental tasks.
Research has shown that dolphins can understand the concepts of numerosity and relative numerosity. In a particular project, see Dolphin Research Center, two participants, Talon and Rainbow, were shown two boards with different numbers of dots on them: 2 and 6 for example. First, they were asked to always pick the board with 2 dots on it, no matter where the dots were on the board or what size they were. Learning this task meant that Talon and Rainbow understood that 2 is different than 6, which is the concept of numerosity (the characteristic of quantity). The next step was to test with other number pairs that were new to the dolphins, and always ask Talon and Rainbow to choose the board that had the fewest dots on it. The ability to pick out the smaller number without being trained on that specific number meant that they understood the concept of "less"(i.e. relative numerosity which is slightly more difficult than numerosity and implies that numbers have a specific order).
Amazingly, dolphins can mimic human actions. Besides humans, only dolphins have demonstrated the abilities of both vocal and motor mimicry. They understand the concept of imitating. Nod your head and the Dolphin does too. Its not just a trick, as they can mimic an action perfectly the very first time they see it. Also amazingly they can relate their own body parts to that of humans, ie. shake your head and Dolphin too will shake its head, wave your arms and the Dolphin waves its pectoral fins, shake your leg and the dolphin shakes its tail, move forward or backward and the dolphin too will move forward or backward. Accurate imitation is rare in the animal world and requires considerable intelligence.
Human language is far more developed and complex than the language of other animals. However several animals are capable of displaying behaviour that could be a forerunner for language (given enough time from an evolutionary point of view). Dolphins are regarded as the most linguistically promising because of their large brain size and the range of sounds they can make. Dolphins have a complex echo-location system. But a large brain is not seen as necessary to accomplish this as bats (small brain to size ratio) also have this ability. The large dolphin brain most likely explains a complex social system. Complexity of social relations in mammals is correlated with brain size and we must remember human language possibly originated as a result of complex social relations.
In dolphin society, dolphins act co-operatively and even appear to display altruistic behaviour. Sophisticated communication (language?) is required for this behaviour. Recent work on wild dolphins (much of the previous research was on captive dolphins which experts say could alter behaviour) has indicated that dolphins can vocalise many sounds, of which only some are used for echo-location. Also, many dolphin sounds are outside the range of the human audible range. It appears that dolphins have a large number of sounds (whistles) that they can combine to convey messages. In teaching dolphins whistles to represent objects, dolphins mimicked the whistles in a way that resembles language acquisition by children. They mimicked the end of the whistle first then the beginning and then combined them, the breaking up method suggesting that the whistles may be components of a larger system.
Experiments with comprehension of word order (where word order affects the meaning of the sentence.
Much research has been focused on language comprehension rather than language production, because comprehension is the first sign of linguistic competency in young children and can be tested in a more controlled manner than language production.
Living in societies requires greater ability to communicate.
Dolphins play and frequently swim in front of boats where they appear to get a kick out of riding on the bow wave and they appear to surf the waves like us for no reason other than pleasure. Play is fun but also the product of an inventive brain and restless mind. Scientists think that for Dolphins play has a crucial role in strengthening bonds within a group.
Dolphins are easily trained and learn exceptionally fast - is this a sign of intellectual ability?
Have dolphins been tested with the 'mirror' test?