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fountains 2: dolphins and their brains

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dolphins and their brains

Here’s the transcript of my second ‘fountains of good stuff’ podcast, ‘dolphins and their brains’, (linked to above) minus some bits at the beginning and end.

Dolphins have long been considered our cute, smart underwater friends. In fact you might be surprised at how far back such observations go, and at how interested the ancients were in dolphinkind. Aristotle recognised that dolphins weren’t fish, that they couldn’t breathe underwater, that they had lungs and had to return to the surface to breathe just like us. The ancient poet Oppius of Corycus had this to say about them:

Diviner than the dolphin is nothing yet created; for indeed they were aforetime men and lived in cities along with mortals, but by the devising of Dionysus they exchanged the land for the sea and put on the form of fishes.

In these remarks we find the mixing of genuine observation and fascination with mythologising which still persists today. Some modern claims are that dolphins are idyllically happy and playful creatures, that they have a special bond with humans, that they’re at least equivalent in intelligence to us, bearing in mind the vastly different medium they inhabit, and that they have a highly developed language and a social and cultural complexity that we’ve barely begun to tap into.

So how much truth is there to these claims? Well I think we should first look at the grandest of the claims, about dolphin language and culture.

Many of the more hyperbolic claims for a rich dolphin language and culture, as yet beyond the ken of mere humans, were made by John Lilly, a pioneering researcher of the fifties and sixties. Lilly worked with bottle-nosed dolphins, and that is the species I’m referring to, though of course, all thirty or so species of dolphins and porpoises, as well as the forty or more species of whales, tend to be lumped in together as highly communicative and cultured.

Lilly’s attempts to back up his claims about dolphin language didn’t work out so well, however, and his writings on dolphins became increasingly drug-influenced and fantastical. Another researcher in the mid-sixties, Duane Batteau, tried to translate Hawaiian phonemes into the whistle-sounds frequently used by dolphins, using them to convey simple instructions. However, Batteau could only use the sounds as holophrases, that’s to say, instructions with complex elements, such as ‘jump through the hoop I’m holding’. The dolphins couldn’t be taught to recognise individual semantic elements within the complex instruction, such as ‘hoop’, ‘leap’ or ‘five feet high’, which are essential to building up a whole language, at least one that humans would recognise, and using it in a flexible and creative way. The dolphins took some years to learn about a dozen holophrastic sounds, which indicated none of the complexity or nuance of human language.

Since these early researches, little headway has been gained in trying to teach dolphins, or any other species, to understand human language, which is hardly surprising, as they’ve evolved to communicate very differently. Dolphins are very vocal animals, forever sounding off with whistles and clicks that are incomprehensible to most of us, and many of which we’re not even equipped to hear. But is this dolphin language?

Well, early research on dolphin whistles didn’t come up with anything too promising. Individual dolphins produce their own unique whistles, described as ‘signature whistles’, doubtless for the purpose of identifying themselves to others. Interestingly, female dolphins develop signature whistles that are quite different from their mothers’, while male dolphins don’t. This is explained by the fact that male dolphins, after weaning, hang around together in ‘adolescent gangs’ just as male humans do [and quite a few other species too, such as elephants]. Females tend to stick to their mothers, becoming young mothers themselves. They need to be able to differentiate between mothers and children, which is unnecessary for the males.

Dolphins do sometimes mimic the whistles of other dolphins too, particularly those of their closest relatives, but signature whistles as a form of recognition and differentiation, are a long way from anything like language. After all, many species can recognise their own mates or kin from the distinctive sounds they make, or from their specific odour, or from visual cues. However, a clever experiment carried out more recently, which synthesised these whistles through a computer, so that the whistle pattern was divorced from its distinctive sound, found that the dolphins responded to these patterns even when produced via a different sound. It seemed that they were recognising names. It’s undoubtedly intriguing, but clearly a lot more research is required.

Most attempts to elicit information about dolphin language, and dolphin intelligence generally, suffer from a difficulty in imagining a language system completely alien to our own, so that we always try to translate communication into something that might make sense to us. It’s a kind of anthropomorphism problem, which we can probably only overcome by a greater insight into the social life of these creatures and what they might use language for. It will no doubt be a long and painstaking process.

One of the reasons given for the supreme intelligence of the dolphin is its very large brain, and on first thought, it seems a very sound reason. The human brain is considerably larger, both in absolute terms and in terms of brain body ratio, than that of other primates.

In fact the human brain has become so large that we have trouble pushing our babies’ heads through the birth canal, and their skulls at birth are still soft and collapsible in places to facilitate the birth process. In the few months after birth, the baby’s head has to be supported until it becomes used to carrying that great bony weight on its shoulders all by itself. The average dolphin brain is slightly larger than ours, but so is its body, so its brain body ratio averages out at about the same, or a little less than ours.

The real key to human intelligence, however, is the growth of a specific part of the brain, the neocortex. In most mammals, the neocortex takes up between 10 and 30% of the total brain mass. In primates in general, it takes up 50%. For humans, though it has climbed to a very impressive 80%. So big is our neocortex that is has to be folded in on itself to fit inside our heads.

So what about the dolphin neocortex? Well, it was John Lilly, the sixties researcher, who first discovered that it was even bigger than our own, a fact that led him to to the quite understandable conviction that dolphins were, at the very least, our equals, intelligence-wise.

However, size isn’t everything, especially when we compare land mammals with their underwater cousins. Mammals on land all have about the same nerve cell density, that is, the same number of neurons per square centimetre. Aquatic mammals have far less densely packed neurons in their brains. In fact, their brains are only a quarter as densely packed with neurons as land mammals, and that’s a big difference. It seems that, because dolphins have evolved in water and don’t have to contend with gravity the way we do, their brains have been able to spread out over a larger area, without necessarily increasing complexity. Which isn’t to say that the dolphin brain isn’t extremely complex. We’re only at the beginning of understanding a small fraction of it.

Some of this research has highlighted that the neocortex in dolphins, which naturally reflects more recent evolutionary development, is used for very different purposes, such as breathing, which is regulated by more primitive brain processes in land mammals. Hearing in dolphins requires a far larger proportion of grey matter than in humans, and it’s likely that their complex sonar system is regulated by the neocortex.

In recent years it’s been discovered that spindle neurons, previously only found in higher primates, exist in large numbers in many whale and dolphin species. These neurons are associated with the processing of emotions and social interaction. They’re relatively large and allow for high-speed communication and response across the large brains of hominids, so the fact that many cetaceans [the order that whales, dolphins and porpoises belong to] have some three times the number that humans do, is certainly food for thought.

“The discovery of spindle neurons in cetaceans is a stunning example of neuro-anatomical convergence between cetaceans and primates,”

says Lori Marino of Emory University in Atlanta, Georgia.

“The common ancestor of cetaceans and primates lived over 95 million years ago, and such a highly specific morphological similarity as the finding of spindle cells is clearly due to evolutionary convergence, not shared ancestry,”

she says. The term ‘convergence’ refers to a similarity in adaptive structures and behaviours in unrelated or only distantly related species.

Exactly how these spindle cells function in cetaceans is still unclear, but it’s believed that they’ve been present in these mammals for some thirty million years, compared to 15 to 20 million years in our primate ancestors.

The term ‘intelligence’ is really quite fuzzy, even when we’re applying it only to humans, let alone comparing humans to such vastly different creatures as dolphins, but years of studying the social interactions of cetaceans in general are gradually revealing a world much worth exploring. However, it isn’t necessarily the playful world we associate with the bounding, squealing, apparently perpetually laughing and eagerly performing creatures formerly associated with marinelands the world over.

Some years ago, beginning in 1997, a growing mystery developed when dead porpoises and juvenile dolphins were found washed up on beaches in Scotland and on the other side of the world in Virginia. The animals had suffered massive internal damage, as it turned out, from dolphin attacks. They had literally been beaten to death. A well-known documentary, ‘the Dolphin Murders’, relates the story. Researchers are still unclear as to the motive for these murderous attacks, but they remind us that evolutionary pressures and brutality are just as much a part of life in the oceans as on land, and that even dolphins, who’ve often been reported as saving human lives at sea, can turn themselves into killers.

Dolphin-hugging, metaphorically speaking, has been all the rage in recent decades, but for all its positivity, it risks obscuring what dolphins really are. They’re not always playful and cute, but they’re certainly among the most fascinating creatures on our planet, and the best compliment we can pay them is to try to get to know them a whole lot better.

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Written by stewart henderson

December 27, 2012 at 12:22 pm

One Response

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  1. […] wrote, or semi-podcasted, on the brain of the dolphin a while back, and much of my focus was on language, often described as the sine qua non of cerebral complexity […]


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