Dolphins are so distantly related to humans that it's been 95 million years since we had even a remotely common ancestor. Yet when it comes to intelligence, social behavior and communications, some researchers say dolphins come as close to humans as our ape and monkey cousins.
In recent years, researchers have found that thought processes in animals aren't a matter of how closely related they are to humans. You don't have to be a primate to be smart.
Dolphin brains look nothing like human brains, Marino said. Yet, she says, "the more you learn about them, the more you realise that they do have the capacity and characteristics that we think of when we think of a person."
These mammals recognise themselves in the mirror and have a sense of social identity. They not only know who they are, but they also have a sense of who, where and what their groups are. They interact and comprehend the health and feelings of other dolphins so fast it as if they are online with each other, Marino said.
At the recent annual meeting of the American Association for the Advancement of Science (AAAS) in Vancouver, Canada, the world's biggest science conference it was said that dolphins should be treated as non-human "persons", with their rights to life and liberty respected. Experts in philosophy, conservation and animal behaviour wanted support for a Declaration of Rights for Cetaceans and believe dolphins and whales are sufficiently intelligent to justify the same ethical considerations as humans. Recognising their rights would mean an end to whaling and their captivity, or their use in entertainment.
Animal intelligence "is not a linear thing," said Duke University researcher Brian Hare, who studies bonobos, which are one of man's closest relatives, and dogs, which are not.
"Think of it like a toolbox," he said. "Some species have an amazing hammer. Some species have an amazing screwdriver."
For dogs, a primary tool is their obsessive observation of humans and ability to understand human communication, Hare said. For example, dogs follow human pointing so well that they understand it whether it's done with a hand or a foot; chimps don't, said Hare, whose upcoming book is called "The Genius of Dogs."
Then there are elephants.
They empathise, they help each other, they work together. In a classic cooperation game, in which animals only get food if two animals pull opposite ends of a rope at the same time, elephants learned to do that much quicker than chimps, said researcher Josh Plotnik, head of elephant research at the Golden Triangle Asian Elephant Foundation in Thailand.
They do even better than monkeys at empathy and rescue, said Plotnik. In the wild, he has seen elephants stop and work together to rescue another elephant that fell in a pit.
"There is something in the environment, in the evolution of this species that is unique," he says.