Carlo Rovelli on what we can learn from the octopus mind

During a boat trip some years ago, a friend of mine who was diving to hunt for octopus climbed back on board with nothing to show, and a slightly troubled air. ‘There was an octopus in a hole,’ he told us, ‘but I didn’t catch it because I lost my nerve: he was staring at me with his big eyes full of fear.’

A few days ago, the Guardian published a list of the ten most important books on the nature of consciousness. Number one, predictably enough, was Daniel Dennett’s classic Content and Consciousness. But the second on the list was something of a surprise – Other Minds by Peter Godfrey-Smith, a book about octopuses. What on earth do these appealing marine creatures, all head and arms, have to do with consciousness?

Accounts like that of my friend are legion in the literature about octopuses. In the laboratories where they are being studied, scientists tell of octopuses capable of opening tins, of clandestinely escaping from their tanks and returning, closing the lid behind them; of recognizing the individual scientists in a research group and spraying the annoying ones with water; of working out how to short-circuit light bulbs when the light bothers them… In natural environments, they have been observed behaving in complex and adaptable ways, and they seem to have the ability to recognize and interpret the attitudes and body language of those around them.

Octopuses have complex intellectual abilities that are decidedly unusual for creatures of their realm and are rather comparable in many respects with those of mammals. They have at their disposal an extremely rich and complex neural network. An octopus may have as many neurons as a dog, or a child. These are the characteristics that make them a valuable case study for those concerned with consciousness.

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‘Consciousness’ is an ambiguous term that has come to mean various things. In the last few decades the phrase ‘the problem of the nature of consciousness’ has taken the place of what in the past used to be the problem of the meaning of soul, spirit, subjectivity, intelligence, perception, understanding, existing in the first person, being aware of a self… Not that these questions are equivalent – they clearly aren’t – and what is meant by ‘the problem of consciousness’ changes from one author to another. But the question of how our subjective experience can arise from natural reality has taken central stage. One reason is that the existence of subjectivity remains the argument most insisted upon by those who, coming from various directions, resist a naturalistic perspective. What is it, in the great game of nature, this ‘I’ that I feel myself to be?

One way of tackling the issue is to observe our non­human cousins. If this doesn’t provide us with all the answers, it can at least help to clarify the question. We have a lot in common with a cat or a dog, and a great deal more with chimpanzees. Hence there are a number of different questions. The first concerns the nature of the capacity to observe, to predict, to interact, to communicate, to suffer and to love – abilities and characteristics that we share with many mammals. The second, perhaps less interesting question concerns what it is, if anything, that differentiates our experience from that of our mammalian cousins. It is one thing to discover how the brain of a cat works; quite another to understand if and how the human brain works in a way that is different to that of a cat. As always, there is no better way of understanding our­ selves than by comparing ourselves with others.

The brain and the behaviour of mammals, however, is too similar to ours, while if we stray too far, to remote biological relationships, we lose something essential to the comparison: we may be able to comprehend in depth how an amoeba works, but this does not give us the impression of having learned much about ourselves. Ideally, we would have an alien race to study, one that had arrived here from another planet, with elements of consciousness recognizably similar to our own but generated by different structures. Perhaps then we could grasp what is essential and what is an accessory to what we call consciousness.

For now at least, such aliens arrive only on the big screen, and these creatures tend to mimic humans in a rather unimaginative way. Sometimes the strangest thing about them is that they defend values that by sheer coincidence our civilization happens to be currently discussing. In truth, we are in a somewhat lonely place: we have nothing and no one with whom to compare consciousness or intelligence, beyond ourselves and our closest relatives. And this is where the octopus comes in.

The octopus is an extremely distant relative. The ancestors that we share with cats go back relatively few generations when compared to the gulf of many hundreds of millions of years that separates us from the ancestors that we have in common with the octopus. The process of separation has radically accentuated our differences, and the octopus belongs to a vast animal kingdom where signs of consciousness and intelligence like our own are quite rare. In that realm, they are exceptional: they have an extremely complex and rich nervous system with a similar number of neurons to mammals, even though they are distant from us in evolutionary terms, having evolved independently. Nature seems to have experimented with the creation of intelligence at least twice: once with our branch of the family, and a second time with the octopus. The octopus, in short, is the extraterrestrial that we have been looking for in order to study a possible in­ dependent realization of consciousness.

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Peter Godfrey-Smith is a philosopher concerned with the nature of consciousness, as well as a passionate scuba diver and a captivating writer. Other Minds is a work of popular science that describes the ingenious behaviours of these extraordinary creatures, and at the same time a convincing book about the nature of consciousness. It argues that consciousness is not something that does or does not exist: it is something that exists in different degrees and different forms: it is a form taken by the relations between an organism and the world.

What interests us about ‘octopoid’ intellectual complexity is not just the similarities with our own, it is also the differences between the two types. The neural structure of an octopus is different from ours: instead of being concentrated in a brain, it is articulated throughout its entire body, including its arms, diffused just below the surface of its body. It is a complex but radically alien intelligence. An octopus tentacle severed from its body continues to exhibit a complex capacity to process information.

An octopus has an amazing capacity to radically alter its skin colours and patterns, changing them rapidly. The colour of its epidermis is controlled by an extremely rich network of diffuse neurons, and the colour changes may also be used as a form of communication. I have no difficulty imagining what it must be like to be a cat. I watch a cat stretching out in the sunshine on a hot summer afternoon, and I can easily identify with that. But what must it feel like to be an octopus, with its brain spread throughout its body and its arms which can each think separately?

In the endless vastness of the galaxies, nature has in all probability given rise to every shape and form, making us one example among many. Who knows how many more complex forms are out there, partly similar to and partly different from ourselves, in the immense celestial expanses? Perhaps there is even one that swims in our seas. And the disturbing encounter that my friend had with the big, frightened eyes of the small octopus was nothing but the spark of an encounter between different kinds… of consciousness.