Dolphins have long been considered to be intelligent, but scientists are only now starting to unravel the true complexity of their brains and behaviour.
In many ways they behave like humans - they form social groups and cliques, they have previously been taught to recognise 'alphabets' of symbols and many have even attempted to befriend us.
Now, a book discusses how this high level of intelligence could stem from the mammals having what's known as a collective consciousness, with the author claiming they 'may know something that we don't'.
The points are raised in Susan Casey's book 'Voices in the Ocean'.
Ms Casey wrote the book after she encountered a pod of spinner dolphins.
She admitted that this first experience made her want to explore the 'strange, enduring, occasionally tragic, and often wonderful relationship between humans and dolphins' and set off to learn more about the creatures.
Dolphins and the 'collective mind'
Over the past 50 million years the brains of dolphins have evolved and expanded dramatically in size.
At the same time, their bodies have shrunk, their teeth have become smaller and they have developed high-frequency hearing.
The limbic system in a dolphin's brain is responsible for the emotions in the same way as it is in human brains.
While most vertebrates evolved this region early and kept it pretty much intact, the system in the brains of dolphins developed further.
Odours, for example, are indistinguishable underwater so the hippocampus of dolphins - a region linked to their olfactory sense - diminished, Ms Casey explained.
'Meanwhile, their paralimbic area grew huge, so densely jammed with neurons that it blurped out an extra lobe,' she said.
'There's a jubilee of tissue packed into this area, an exuberance of grey matter that scientists believe relates to all things feeling - and no other mammal has anything quite like it.'
During an interview with neuroscientist Lori Marino, Ms Casey asked whether the animals' nature was the reason why dolphins have such large brains.
Ms Marino said this unique evolution suggests the animals are 'doing something very sophisticated or complex while they're processing emotions' and their brains may have adapted for a type of connectivity unprecedented in the animals kingdom.
Ms Marino calls this a 'collective soul'.
'When you look at their brain you can definitely see how this could be an animal that takes sociality to another level,' Ms Marino told Ms Casey.
She used the example that dolphins and whales strand en masse when only one or two individuals are sick and when they're herded together they huddle in a group rather than jumping nets.
'There is some sort of cohesiveness in them that I don't think we get quite yet, but it accounts for a lot of the behaviour that seems strange to us,' she continued.
'I think a lot of it comes down to emotional attachment.
'And I think there is a very strong sense in them that if something happens to the group, it happens to you.'
The possibility of a dolphin collective soul was first proposed in the 1980s by paleoneurologist Harry Jerison. He referred to this as as 'the communal self.'
However, 'collective consciousness' in other animals has been discussed for more than a century.
The idea was first presented by French sociologist Émile Durkheim in 1893, but his definition related more to a shared understanding of certain morals and social norms based on people either imitating others, explicitly passing on these behaviours to one another, or agreeing certain ideals in order to feel accepted.
It is often referred to as a group having a 'shared mind' or 'hive mind'.
Yet in the 1970s, scientists began to suggest that this collective consciousness could be developed and spread through species non-explicitly, through telepathic or 'supernatural' means.
Monkeys in Japan, for example, were shown to have adopted and developed certain identical behaviours without ever coming into contact with one another.
Blue tits in Europe exhibited similar so-called telepathic behaviours, suggesting they were sharing ideas.
Ms Marino continued: 'In fact, dolphins are so tightly bound to their pods that they may be operating with a degree of interconnectedness far deeper than our own.'
Befriending humans: The social needs of dolphins
The dolphin's behaviour, on the other hand, may not be a sign of a collective mind, or telepathy, but instead a much higher state of social intelligence compared to other animals, namely humans.
'In any group of dolphins you’ll find cliques and posses, duos and trios and quartets, mothers and babies and spinster aunts, frisky bands of horny teenage males, wily hunters, burly bouncers, sage elders - and their associations are anything but random,' Ms Casey said in her book.
'They’re also highly social chatterboxes who recognise themselves in the mirror, giggle, feel despondent, stroke each other, adorn themselves, use tools, introduce themselves, rescue one another from dangerous situations, form alliances, throw tantrums, gossip, scheme, empathise, seduce, grieve, comfort, anticipate, fear, and love - just like us.'
These similarities may explain why dolphins are so keen to befriend humans.
Tales of dolphins befriending humans are said to date back as far as AD 77 when Roman naturalist Pliny the Elder recounted a story about a dolphin who formed a bond with a boy who fed him bread.
Aristotle even wrote offhandedly about the dolphins' 'passionate attachment to boys'.
As Ms Casey described in her book: 'When you consider how risky it is for dolphins to spend time in close proximity to people, it is all the more intriguing that so many human-dolphin stories have similar themes: dolphin seeks out man, dolphin wants to play with man, dolphin assists man, dolphin rescues man.'
She refers to one dolphin in particular called Fungie, the Dingle dolphin.
According to local legend, the bottlenose dolphin has been swimming in Dingle bay, Ireland since October 1983.
Despite the dangers of the bay, including heavy boat traffic and fishing trawlers, people claim to have spotted Fungie almost every day.
He is always seen alone, however, suggesting he is not part of a pod like other dolphins.
Ms Casey explained this behaviour may be a sign that dolphins behave towards humans the same way they do towards one another.
'In other words, dolphins do not always differentiate between us and them.
'Maybe that was why Fungie had made his home among the residents of Dingle,' she said.
'To him, perhaps, they were just a slightly peculiar-looking pod.'
Dolphins have even been known to bring fish and other 'gifts' to humans which feed them, particularly at the Tangalooma Island Resort in Australia.
Dolphins: Lifesavers of the sea
Whether it's a social need for the dolphins to connect with a species it sees similarities in, or a strong desire to interact with any species, the creatures have a reputation for being keen lifesavers.
Ms Casey's book features a number of anecdotes of dolphins breaking away from boats to encircle and rescue the bodies of people who had attempted suicide or become stranded at sea, sometimes miles away from where the dolphins were.
One example, quoted from the book 'Beautiful Minds' by biologist Maddalena Bearzi, recalls a story in which dolphins supposedly beckoned a group of divers out to sea and away from the coastline of Thailand on the day the tsunami hit in 2004.
The divers were unaware of the dangers on the shore and claim the dolphins effectively saved their lives by keeping them out at sea.
If they do have a collective consciousness, with or without telepathic abilities, the animals may have been able to 'sense' that someone was in danger.
And if theories about the animals not being able to differentiate between humans and themselves are true, they may have responded to a lone human in the same way they would a lone dolphin that had been separated from its pod.
Are dolphins really that smart?
Not all scientists are in agreement with Ms Casey, however.
A study from neuroethologist Paul Manger of the University of Witwatersrand in South Africa claimed that behavioural studies involving dolphins are flawed and therefore not very informative.
'We put them on a pedestal for no reason and projected a lot of our desires and wishes on them,' said Professor Manger. 'The idea of the exceptionally intelligent dolphin is a myth.'
Whereas goldfish placed in a bowl try to jump out to freedom, dolphins rarely try to escape when they are caught in nets.
While zoologists have observed that dolphins can distinguish between the concepts 'many' and 'few', he suggested the same ability has also been demonstrated in yellow mealworms.
He continued that evidence which shows dolphins have learnt sophisticated 'tool use' is 'flimsy' because it is based on the fact bottlenose dolphins on Australia's west coast have learnt to hold sponges in their snouts to help them find food on the ocean floor.
'Exactly what the dolphins do with the sponges remains unknown,' he said.
While researchers have been able to teach bottlenosed dolphins to recognise an 'alphabet' of as many as 40 symbols, Professor Manger pointed out that African grey parrots and California sealions have also managed the same feat.
And while much has been made of the dolphin's ability to identify itself with a 'signature whistle', experts now say this is not a complex language, and say it is no more unusual than the tail-wagging dances of bees or 'signature' accoustic signals made by other marine animals.
At the time of the report, Karsten Brensing, a marine biologist with the organisation Whale and Dolphin Conservation (WDC), said: 'To put it bluntly, most of that is b*******.
'You can use similar arguments to prove that people aren't intelligent.'
'One of the great marine scientists, Ken Norris, described dolphins as "the most mysterious of fauna on the planet" in the 1960s,' Ms Casey told MailOnline.
'Since then we’ve learned much about these animals: we’ve examined their formidable brains, we’ve charted their amazing evolution, we’ve tested their cognition in every way we can think of, we’ve observed them in the wild.
'We know that dolphins are self-aware, that they have distinct and stable personalities, that they call themselves by name. So that makes our relationship more informed, but at the same time we’ve learned all these impressive facts about dolphins, we’re making their lives increasingly hard.
Dolphins contend with many threats [and] my hope is we can take all our knowledge about them and distill it into wisdom.'
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