I'm a sucker for cephalopods | Peter Godfrey-Smith

My book Other Minds had its origins in a series of encounters with some unusual animals. The encounters took place in the ocean around Sydney, Australia, and the animals were cephalopods – members of the group that includes octopuses, cuttlefish, and squid. I hadn’t been looking for these animals, or planning to become obsessed with a wild bunch of molluscs.

The meetings began by chance, when I came across them in the water. I had a vague knowledge beforehand that these animals were unusually “smart” compared to other invertebrates, but my early encounters with them were still startling.

More than half of the neurons in an octopus are not in the animal’s brain, but are spread through the body

The first ones I met were Giant Cuttlefish, hovercraft-with-tentacles that can produce just about any color on their skin, and change their colors and patterns in less than a second. Then I began to come across octopuses, as they fastidiously arranged objects in front of their dens. I found that when I hovered in front of these animals in the sea, they often seemed interested in me – watchful, inquisitive, and engaged. There seemed to be a lot going on inside them.

The picture we’ve often been encouraged to have of animals very different from us – especially invertebrates, which lack backbones – is that they are little robots, or perhaps even less than that. Biology is now uncovering hidden complexity in the behavior of a wide range of animals, but cephalopods are a special case. To get an understanding of their place in the scheme of things, it’s helpful to zoom out and think about the history of animal life as a whole.

The evolution of animals has the shape of a tree, a series of branchings in which one species or population splits and gives rise to two. After a split, the species one each side will diverge, and if they survive, they may eventually split again. One of these branchings in the history of animals occurred perhaps 600 million years ago. A population of small worm-like creatures split, and the two sides gave rise to two great branches of the animal tree.

One branch includes ourselves and other vertebrates, such as other mammals, birds, and fish, while the other branch includes insects, crabs, earthworms, and many other familiar invertebrate animals. On that other side, most of the animals have simple brains (if any) and small nervous systems, but cephalopods are the exception. They have nervous systems as large as those in many vertebrates, but evolved these on an entirely separate line

Did cephalopods end up similar to us, or entirely different? There’s a combination of similarities and differences. Cephalopods are very visual animals, and their eyes are built on a similar design to ours – we both have “camera” eyes. But behind those eyes are brains of entirely different organization.

When I hovered in front of these animals in the sea, they often seemed interested in me – watchful, inquisitive, and engaged

And to say that even understates the case; more than half of the neurons in an octopus are not in the animal’s brain, but are spread through the body, especially in the arms. Each of those eight arms is covered in sensors; their suckers can taste you, as well as grip you. The details of the movements of each arm, and perhaps some whole motions, appear to be locally controlled by the arms themselves. An octopus might be a very different kind of self, a different kind of agent, from an animal like us.

But when you interact with them, you also see similarities. Octopuses have an exploratory way of dealing with the world. Some of them play with objects, for long periods of time. They like novelty to an extent that is unusual in non-human animals. This inquisitive, attentive manner is one of the things that makes it seem inescapable to me that there is something it feels like to be them.

Trying to get into their heads was hard, but the roaming arms and fluid bodies of octopuses also posed another kind of challenge. Other Minds has photos as well as text. Giant Cuttlefish must be some of the most photogenic animals on the planet, with their alien bodies, deep reds, and intricate patterns. They were easy. Octopuses, however, I found very hard to photograph. Their bodies, like their minds, often seem to have no centre at all.

Many of the octopus photos in the book are frozen instants from videos. When I’ve been able to get a proper octopus portrait, the moment has often been one in which the animal pauses, pulls itself together, and stares back at me. In such moments we each reach across a great gulf in the tree of life.

Peter Godfrey-Smith’s Other Minds: The Octopus and the Evolution of Intelligent Life (William Collins, £20) is out now