I had previously read, Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness. Metazoa, compared to that book, attempts to take a wider perspective on the emergence of animal minds. The main goal of Metazoa is to try to make progress into the guesswork behind what other animal minds are likely to be like, which has ramifications for ethics and how we think of minds and experience more generally. This work requires some way of bridging the gap from materialist views of biology to the experience of minds, which has traditionally been described as "the hard problem." Godfrey-Smith provides his thesis of how to tackle this problem towards the beginning of the book: "The evolution of complex life naturally gives rise to the mind, through the growth of purposeful action and sensitivity to the environment." So to me, it sounded like he was saying that the best way to guess about what it is like to be another animal is by studying an animal's behavior and its sensation/perception systems, which, to be honest, I personally had a hard time seeing how that is any different from the usual approach.
Because he wants to link mind with the evolution of complex life, he weaves discussion on phenomenology through a gradual discussion of the evolution of life.
The first chapter, protozoa, discusses the concept of a "self" as being a fundamental building block of life. The argument is that cells can be thought of as selves because they organize and control storms of electrical and chemical activity to meet their own needs. Even these single cells have ways to sense their environment and to move in accordance with those sensations, which gives the protozoa agency. Godfrey-Smith argues that the colors and flavors of this agency define what the mind looks like.
For example, the glass sponges and corrals, the subjects of the next two chapters, have the limited ability to adaptively respond to their environments. Godfrey-Smith shows through the discussion of polyps how action programs, like grasping, can be co-opted for movement and drive evolution.
Godfrey-Smith proposes that subjectivity, which is an important part of how we think of minds, evolves alongside of agency. As the nervous system develops along with early muscles in corals, anemones, and jellyfish, animals gain the ability to coordinate activity across the whole animal, which lead to more sophisticated possibility of action.
In the one-armed shrimp, Godfrey-Smith discusses arthropods and makes the argument that at this level, forms of available action require the animal to understand the difference between actions made by itself compared to actions made by other things in the world. He gives examples of eyes moving around a room, where the sensations on the eyes are changing very rapidly, or when a shrimp momentarily grabs itself with an arm, but then lets go. These kinds of actions require that there is some subjective knowledge, that there is a "subject" that does these things, which is different than simpler actions - like say using a single swimming action to go towards a light or a chemical gradient.
Godfrey-Smith talks about how in the Cambrian period, about a 540 million years ago, animals started to scavenge and predate on other animals for the first time, which drove the evolution of more sophisticated action and sensing programs that give rise to this new, necessary "point-of-view."
Godfrey-Smith is doing all this work in making us start to feel like shrimps and spiders are similar to us in their probable sense of subjectivity, but then he seems to use the octopus to remind us that, in fact, there are reasons to think that animal minds would differ quite substantially. He uses the structure of the octopus nervous system, an animal whose anatomy and behavior he knows well, as a case example. The octopus has a much more decentralized nervous system than ours, with ganglia controlling each leg, but connected to each other. This discussion dives into a deeper question of how disconnected regions may act as separate selves for separated actions, but may merge when actions are coordinated, and brings in evidence from split brain patients and other examples in nature of animals with minimal connections between major brain areas.
We get even closer to our own brains in the discussion of the centralized vertebrate brains that began in fish. Through this section there is discussion on other sensory abilities, especially electrosensing, which sort of clunkily leads into philosophical thinking about fields that lies at the basis of Godfrey-Smith's speculations about what defines consciousness. This was the notion that I personally found myself most vehemently disagreeing with and even seemed contradictory to other statements that Godfrey-Smith made, but he continues returning to the idea for the rest of the book, even using it to justify why an AI agent isn't allowed the same consciousness as his beloved animals.
The account of biological evolution is more coherent than the mechanistic discussion of consciousness and picks up again with the transition of animals from sea to land, which created another burst of animal innovation. I really liked the sense of inevitability that we get from the account. The chemical properties of water make it necessary for life to first evolve in the ocean, but once life is complex enough, it may be capable of adapting to the land. Adapting to the land comes with huge rewards because the amount of energy available from the sun and oxygen levels are much higher.
The transition to land opens up a new field for evolution to adapt new kinds of bodily actions and ways of manipulating things, as well as new relationships to plants and other animals. This part of the book also spends a lot of talking about animal cognitive abilities and how different animals solve different types of problems. That topic turns into a discussion of pain, emotions, and moods, and provides evidence that even arthropods and gastropods may experience these things. I really appreciated the introduction to behavioral paradigms used to study pain, which included observations of tending wounds, pursuing analgesics, accepting pain more readily in situations where there is some additional future reward or threat, and being more pessimistic about the possibility of reward after injury. I also liked that Godfrey-Smith proposes a plausible reason why some animals may not benefit from evolving pain - particularly short-lived animals, like adult insects, who need to reproduce extremely quickly before dying. However, I sort of felt like Godfrey-Smith was trying to sneak something past me, because he would consistently remind us that we shouldn't simply trust animal behavior, since we have a tendency to view behavior too much from our own perspective…but then he would support all of his own arguments about animal experience through behavior.
The end of the book introduces one of the last fundamental elements of mind, which he calls a difference between online and offline processing. This concept differentiates making actions in the present vs. modeling the future and the past through learning. He connects this process to sleeping and especially REM sleep, with the implication that animals that have something like REM sleep probably have something like the ability to "go offline" and imagine or remember, including states that exist in cephalopods. He ends with a straightforward discussion of ethics that should reconsider animal pain and experience - although, I thought he was pretty conservative with his recommendations after the rest of the book…he explicitly says, "the aim of this book is not to argue that we need to radically change our behavior towards animals of those kinds” …referring to insects, gastropods, and the like earlier.