Metazoa Animal Minds and the Birth of Consciousness

In 2016, the scuba-diving philosopher Peter Godfrey-Smith wrote Other Minds where he explored the mind of the octopus – I reviewed it right before reading this book. Its bestseller status, including translations in more than 20 languages, was not entirely unpredictable. Octopuses are a sexy topic. Four years later, he explores animal minds further with Metazoa, with the tour now also including sponges, corals, shrimp, insects, fish, and mammals. Godfrey-Smith convinced me he is no one-trick pony when it comes to writing a good book, though this one is more cerebral than its predecessor.

Subjective experience, sentience, consciousness – Godfrey-Smith uses these terms fairly interchangeably here, writing that “our present understanding is not good enough to insist on one language or another” (p. 19). Whatever you prefer to call it, what this book builds toward is a picture of gradualism: these did not just pop into existence out of nowhere, but gradually came more and more into focus during the evolution of life. He admits that this puts him at odds with currently popular ideas in philosophy. The first chapter, then, does an excellent job at situating the reader. It provides an introduction to the history of thinking on minds in humans and other animals. One problem is that you will find a wild variety of views, from panpsychism holding that everything down to atoms is sentient to some degree, to those who see it as something exclusively human. And one can argue, pretty much without impunity, for anything in between. Godfrey-Smith’s approach is one of biological materialism, that is, he is convinced that these mental phenomena are manifestations, rather than results, of more basic biological, chemical, and physical activities. “Brain processes are not causes of thoughts and experiences, they are thoughts and experiences” (p. 20). This introduction also highlights the complexity of this project (i.e. understanding the mind) and the fact that many questions will remain unanswered by the end of the book.

The above is the broad brushstrokes picture of Metazoa: minds evolved gradually. But how far back do we have to go see the first steps in this process? My impression is that he situates it further back in time than Feinberg and Mallatt did in The Ancient Origins of Consciousness (a far more technical book than this). Godfrey-Smith starts with sponges and the basics of neurobiology: how ion channels in cell membranes can result in chain reactions known as action potentials by which neurons communicate. His descriptions of the inner workings of cells and how things work very differently on a nanoscale compared to our everyday experience, are evocative.

Other than pumping water through their body, sponges do not do very much by animal standards. A game-changer that arrived with cnidarians (corals, anemones, and jellyfish) was that of muscle-driven action. On the philosophical side of things this means exploring the concepts of agency and its complement subjectivity. But it also allows Godfrey-Smith to revisit and re-examine the Ediacaran (~635-540 million years ago) and the now widely accepted divisions in it. Life, it seems, was still in the process of getting the hang of this whole multicellularity business, ramping up to the Cambrian and its explosion of lifeforms, though he shows himself pleasantly up-to-date by highlighting the ongoing discussion on how sudden this explosion actually was.

That notwithstanding, while the cnidarians were strong on the agency-side of things, the next important group, the arthropods, evolved a good deal more of sensing and thus subjectivity. Shrimp, crabs, and other crustaceans are festooned with antennae and other sensors. With sensing and acting on a multicellular level came new complications and an increased need to tell self from other. Writes Godfrey-Smith: “It gives rise to a new way of being in the world. It involves the establishment of a point of view, a perspective in a new sense.” (p. 87). And if I have grasped his line of thinking so far, this is where concepts such as agency and an animal experiencing itself as a subject in the world come into increasingly sharp focus.

The octopus chapter retreads some of Other Minds but also adds new insights. In particular, octopuses, with their hybrid centralised-decentralised nervous system, are less integrated than arthropods. Just in case you were entertaining the idea that evolution is goal-directed, nature throws the octopus at you as an example of a life form moving in a different direction.

Most of the book focuses on early marine invertebrate groups, with vertebrates only coming into the picture about two-thirds in. These are pretty heady chapters. Starting with fish, we find the centralised brain typical of vertebrates. One particularly interesting aspect is the degree to which the left and right halves of the brain are connected. Mammals, excluding marsupials, have a strong connection via a thick nerve bundle known as the corpus callosum. The connection between brain halves is much weaker in other vertebrates. Godfrey-Smith uses observations made on human split-brain patients, where it seems there are two minds housed in one body, to ponder what this means for the experience of being a fish or a reptile.

Godfrey-Smith leaves the reader with plenty of fascinating questions. There are several strong points to his narrative. First is his grasp of evolutionary biology. Despite the book’s organisation, he repeatedly reminds readers that just because animals such as sponges and corals are simpler in their organisation, they are not more primitive. The living members of these groups have been subjected to as much evolutionary time as us. They are our cousins, not our forebears. Second is that the same care for the reader shines through as in Other Minds; in the way he explains things, the way he regularly zooms out to take stock of where in the story he is. He tries his hardest to make sure that you do not get lost. And thirdly, some of his observations made during scuba-diving are incredibly funny. That said, you will find no illustrations of the different invertebrate nervous systems and vertebrate brains through evolutionary time – as a philosopher, this is a level of detail he leaves for neurobiologists.

Compared to Other Minds, Metazoa dives deeper into neurological and philosophical topics: qualia, pain, emotions, types of memory, and others. It is, altogether, a more challenging book, though in a stimulating way. I am not sure it will have the same wide appeal as Other Minds, but for those readers interested in joining him on his quest to understand the evolution of mind, consciousness, and subjective experience, Godfrey-Smith delivers in spades.