In this book Peter Godfrey-Smith from the University of Sidney speculates about the evolution of consciousness based on his belief that the octopus evolved its own form of intelligence and sentience.

The book is clearly a passionate account, and it should not be taken as a scientific text. One page after the other we are given speculation based on the speculations of the previous pages. The cumulative chance that his speculations are correct ends up being very low. Sometimes the language itself is confusing. For example, a key chapter discusses how consciousness differs from "subjective experience" (what it feels like to be what you are). He sees consciousness as one kind of "subjective experience", which is fine, but two sentences later he uses the term "sentience", and it is not clear is sentience is now a third thing or a synonym of consciousness or what. And what does "subjective experience" exactly refer to? My personal, individual feeling of being me, or the fact that humans feel human whereas cats feel like cats? Is it related to the way an entire species "feels" or to the individual feeling of the self?

The book begins with a speculative history of life on Earth. Life on Earth began about 3.8 billion years ago but for 2.8 billion years life was pretty insignificant, multitude of single-celled organisms (like bacteria) probably living in seas. Then about one billion years ago animals appeared, with their ability to move around. Godfrey-Smith points out that light has a dual role for life: on one hand, it is a source of energy, on the other hand it helps "see" things. (I am not sure that this is really true: is light a source of energy for you? I doubt it, certainly not as significant as your favorite food. Indirectly, yes. But that's like saying that the supermarket is a source of energy). He speculates that at some point cells became able to detect chemicals released by other living beings, and eventually some chemicals became officially a signal for other beings. Primitive organisms began to sense the environment and to signal to other organisms. He then speculates that sensing and signaling became internalized for sensing and signaling among the parts of the organism. This is left a big vague. Then he speculates that sponges are the ancestors of all animals. He adopts Chris Pantin's theory that the nervous system originated for internal coordination but combines it with the traditional view that it originated to control action based on senses (the sensory-motor theory). He speculates that the first animal with a nervous system was something like a jellyfish. He then states that the "Cambrian explosion" of species that took place about 524 million years ago was mostly about bilaterally symmetric animals, and that these animals are particularly well-suited for complex behavior. He does not elaborate on these statements so we have to trust that most experts agree. He thinks that it is during the Cambrian that each animal becomes an "important" part of the environment of other animals, and that then the "mind" evolved in response to other "minds". This is vague and confusing because "important" is not defined (animals already coexisted before the Cambrian) and one sentence later "mind" is defined as "the senses, the nervous system and the behavior", which may or may not be your definition of "mind". He then concludes that the Cambrian caused an information revolution because organisms had a lot more to process now that they were aware of other organisms. At this point two nervous systems evolve: one to track light, which is used to regulate biorhythms, and one to control movement/behavior. This is an interesting idea, but, again, just that: an idea.

We then get to the octopus, the protagonist of the book. He thinks that octopuses developed an intelligent brain following a different evolutionary path than the one followed by mammals and birds. He spends a few pages describing his personal experience with octopuses but more importantly he tells us that octopuses have large brains: 500 million neurons. The difference is that their brain is spread all over the body. Some of our neurons are not in the brain, but in the case of the octopus it's even difficult to tell which part is the brain because neurons are everywhere. He thinks that octopuses acquired a large brain because they lack a rigid body and therefore the possibilities of movement are astronomical. So he thinks that neurons multiplied simply to coordinate the body and only later did such a large brain become useful for other tasks. The octopus became "intelligent" because of "mental surplus". It is only in passing that he mentions another possible cause: octopuses are very vulnerable, not having a shell to defend them. Any animal who is so vulnerable is either very intelligent or... extinct.

He thinks that the "subjective experience" of a species was born gradually by the evolution of "sensing, acting and remembering". He quickly relates his views of the origin of consciousness to Bernard Baars' theory of the "global workspace" and argues that experiments by Stanislas Dehaene have confirmed it: things have to be in the global workspace for us to be conscious of them. Godfrey-Smith thinks that a global workspace is not needed for subjective experience. First there was subjective experience, and then all the rest of internal mental life evolved. Whichever the underlying theory, his empirical evidence is basically that octopuses seem to behave intelligently. For example, they are curious. Their intelligence evolved in a different way but also represents a general idea: that the brain is not the controller in charge of everything but a partner in a complex system of cooperating organs (as argued by Hillel Chiel and Randy Beer in their 1997 paper "The brain has a body").

The most interesting chapter is the one on "color". Octopuses are masters at camouflaging but, more importantly, they use color to signal. It could be that they evolved the skills of camouflaging simply to defend themselves from predators but then started using that skill to communicate their "feelings". Godfrey-Smith basically hints at the existence of a visual language, which would in fact be infinitely more complex than the audio language that most mammals and birds use because an image is made of millions of pixels.

Somehow this leads to a discussion on the origin of inner speech, that he argues could be found in the efference copy mechanism, the way the brain makes internal copies of its actions (so that it can compare intended action with the actual action, i.e. what we hear us saying when we speak).

There is one lengthy chapter about why animals age, and why they die at such different ages.

He combines effects discovered in the 1940s and 1950s by Peter Medawar and George Williams, and later given a mathematical foundation by William Hamilton, to prove that it makes sense for octopuses to have very large brains and very short lives.

This too has to do with the fact that at some point in the history of life, cephalopods abandoned their protective shell. But I don't think that Godfrey-Smith provides an explanation for why octopuses discarded their shells in the first place.

It's an interesting book with a lot of interesting ideas, but not even close to a scientific proof of anything.

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