New research suggests the belief that they possess high intelligence may be due, in part, to a look that makes it appear as if they are always smiling.
Zoologist Justin Gregg, author of Are Dolphins Really Smart?, said: “In terms of intelligence they are nowhere near as special as they have been portrayed.”
US neuroscientist John Lilly first proposed the theory that dolphins were particularly intelligent in the 1950s after his experiments concluded the animals were trying to communicate with researchers.
Sixties TV series Flipper, which featured a crime-solving dolphin, added to the perception of intelligence.
Last year, scientists told the American Association for the Advancement of Science that dolphins should be reclassified non-human “persons” and killing them treated as murder.
In terms of intelligence they are nowhere near as special as they have been portrayed
But Gregg, a researcher with the Dolphin Communication Project in America and co-editor of journal Aquatic Mammals, believes that although dolphins show signs of complex behaviour – such as living in large social groups, empathy and communicating with peers – these traits are also found in chickens, pigs and bears.
Gregg said researchers had made mistakes, most crucially that dolphins’ large brains equal greater intelligence and that the complex sounds they make are a form of language.
Dolphins have also been portrayed as gentle – but research at St Andrews University recorded how bottlenose dolphins often kill smaller harbour porpoises.
The leader of one pod of dolphins even became known as Jack the Flipper.