The nature of consciousness is one of the hardest problems in biology. What exactly is it? Where did it come from? And are non-human animals conscious? Philosophers and scientists range from ascribing consciousness to all life (biopsychism), or even all matter (panpsychism), to attributing it exclusively to humans. Seemingly beyond the purview of empirical science due to its subjective nature, there is a lack of “intuitively attractive solutions” (p. xiii). In the opinion of Walter Veit, an assistant professor in philosophy, that just will not do. In this slim but advanced-level book, he outlines a mightily interesting thesis of how consciousness could have gradually evolved, which aspect of it likely appeared first, and why we urgently need to step away from taking human consciousness as our yardstick.

A Philosophy for the Science of Animal Consciousness, written by Walter Veit, published by Routledge in June 2023 (paperback, 144 pages)

Before we delve in, I note that several parts of this book have been previously published as articles and are here extended and improved upon. Given the above-mentioned wild sweep of alternative views, it might help to start by situating Veit’s ideas amidst his peers. I am doing this with the caveat that my background is in evolutionary biology, not philosophy, so bear with me while I try not to make a hash of this.
– First, Veit is a materialist: consciousness is a neurological phenomenon explainable in terms of biological matter. I have to stop myself from writing that the brain produces consciousness; “in a biological materialist picture of consciousness, subjective experience is constituted by particular mechanisms and processes of the nervous system. It is not “produced” by it” (p. 38). I think Ed Yong said the same in about an animal’s sensory world: “it is not separate from the body, but of it” (p. 333 therein). In case you are familiar with the movers and shakers in psychology and philosophy of biology, Veit’s style of philosophy fits alongside e.g. Kim Sterelny & Paul Griffiths, Peter Godfrey-Smith, and Daniel Dennett. It clashes with e.g. Thomas Nagel (of that famous 1974 paper) and David Chalmers who see an explanatory gap between mind and matter and call it the hard problem of consciousness.
– Second, Veit is a gradualist: consciousness did not appear suddenly but evolved gradually. As with other biological phenomena, we should expect “gradation and variation of it across the tree of life” (p. 24). This situates him close to (again) Godfrey-Smith, Frans de Waal, Michael Tye, and Todd E. Feinberg. Veit specifically wants to heed the late Donald R. Griffin‘s call for a cognitive ethology: “to study consciousness […] as an adaptive and evolved phenomenon in nature” (p. 15).

So, having characterised Veit’s ideas and his mission in this book (to give an evolutionary account of the origins of consciousness), how does he go about this? For consciousness to evolve by natural selection, it had to be a trait worth having. In other words, we need to answer “the functionalist question of what consciousness […] does for healthy sentient agents” (p. xiii). Veit’s answer to that? “The function of consciousness is to enable the agent to respond to pathological complexity” (p. 2). I admit that I struggled with the term “pathological complexity” as I find neither the term nor the link he makes between health and consciousness intuitive. Veit immediately admits this. Equally adequate and less confusing would be the term “life history complexity”. That is a term I can work with. Life history theory studies how organisms deal with the trade-off between growth and reproduction. Given a limited energy budget, you cannot maximize both. However, there are many different solutions to staying in the game of life by achieving reproductive success, which explains the mind-boggling diversity of life history strategies we observe around us.

“For consciousness to evolve by natural selection, it had to be a trait worth having. In other words, we need to answer the question of what it does for healthy sentient agents”

Having answered the question of what consciousness is for (to deal with life history complexity), you may well ask: when did life history become so complex? Veit argues that this happened during the Cambrian explosion, that slow-motion diversification of animal body plans that started some 539 million years ago. This resulted in a computational explosion in life history choices, creating strong selective pressures for the evolution of consciousness. But what of the preceding Ediacaran? Modern thinking increasingly questions how much of an explosion the Cambrian really represented and whether complex multicellular animals evolved earlier. Veit concedes to this but argues that for a long time, we see no signs of adaptations to predator-prey interactions. Until the Cambrian, that is. In my opinion, this is not that important a detail. Where exactly in time we situate Veit’s computational explosion does not change the logic of the argument. Note that, as opposed to some others, he veers away from positioning it much earlier in time and granting consciousness to single-celled organisms.

Okay, we have a “why” and we have a “when”, but we have so far skirted the “what”. What is consciousness exactly? Though Veit does not attempt the impossible by trying to define it, he does emphasize throughout that the human subjective experience cannot be our yardstick. For too long, research on animal consciousness has been held back by a top-down approach that asks how human-like other minds are. Instead, he advocates a bottom-up approach. Frans de Waal has elsewhere compared consciousness to an onion, consisting of layers. Veit here runs with that metaphor and takes a “reverse-engineering approach [that asks] for the most minimal form of consciousness” (p. 42). For this, he elaborates on the 2020 paper Dimensions of Animal Consciousness by Birch et al. who propose five aspects. Though we could argue endlessly about the exact number and kinds of dimensions, Veit thinks that there is nothing to be gained by trying to pin this down now. This is just a starting point for much-needed empirical work and can be refined later.

A large chunk of the book explains these five aspects and starts peeling back the layers, discarding them in sequence until there is only one left. The one-sentence summary of this is that he considers diachronic experience, synchronic experience, self-consciousness, and sensory experience to be later add-ons to a core built on evaluative experience. Let me say that again, but slower.
– Diachronic experience is the integration of experience across time (in humans this includes mental time travel) and is most easily put aside as a higher-order feature not present at the start.
– Synchronic experience describes how we experience a single self that receives all sensory input. However, several animal groups have brains that are more lateralized, resembling human split-brain patients. Their experience is likely more disunified without it being dysfunctional.
– Self-consciousness is the awareness of oneself as distinct from other beings and the outside world. Though it is easy to see how it evolved as organisms became more active agents, Veit does not think it lies at the origin, and it is hard to see how the remaining two arose out of a sense of selfhood.
– Sensory experience, the conscious awareness of what we perceive with our senses, is the other popular dimension of choice for many neuroscientists and philosophers as the root of consciousness. Veit contends that it, too, cannot explain how the other two arose out of it. Also, much sensory perception happens unconsciously.
– Given this stalemate, Veits suggests we consider evaluative experience. Some authors speak of emotions and moods, though Veit prefers the term hedonic valence, or simply put, whether something feels good or bad. This requires neither self-consciousness nor sensory experience.

“consciousness [has been compared] to an onion, consisting of layers. Veit here runs with that metaphor and […] starts peeling back the layers, discarding them in sequence until there is only one left.”

The payoff, especially for a biologist such as myself, comes in the chapter where Veit reverses his reverse engineering, as it were. He returns to the discarded dimensions to see if there are animal groups that possess only some of them and looks at gastropods, insects, cephalopods, fishes, reptiles, and corvids. This shows how, starting with just evaluative experience, sensory experience could quickly have evolved as an enrichment of evaluation. Selfhood could in turn have evolved as an enrichment of sensory experience. An evolutionary perspective can answer other puzzling observations. Take, for instance, the striking difference between the life histories of insect larvae and adults. The former focus on survival and are sensitive to pain, the latter focus on reproduction and seem unbothered by loss of limbs and other gruesome injuries, even if there is evidence that they respond to harmful stimuli with aversive responses and longer-term negative mood swings. An evolutionary perspective is also compatible with the loss of certain aspects of consciousness with time. What ultimately counts for an organism is the adaptive value; there is no march of progress here towards human-style consciousness.

The above is but a quick-and-dirty summary. Out of necessity, I have skimmed over many subtleties, objections, and responses to these. Hopefully, however, it gives you an idea of whether this is a book worth pursuing. A word of advice: do not let its 122 pages fool you, this is a slim but dense volume. In my earlier reviews of Godfrey-Smith’s books, I described Metazoa as a step up from Other Minds. Given the agreement between Veit’s and Godfrey-Smith’s views, how appropriate to suggest that this book in turn is a step up from Metazoa. It is squarely aimed at advanced-level students in philosophy, psychology, and cognitive sciences. If terms such as phenomenology or valence are not part of your daily vocabulary, you might find this work challenging. Despite the jargon, it is written with flair. It is also very clearly structured. Each chapter, and the book as a whole, outline what will be discussed, discuss it, and then summarise what has just been discussed. Furthermore, I appreciate that Veit remains humble and tones down the ambition of this project. This book is not intended to rule out other theories on the origins of consciousness. Rather, it seeks “to undermine an almost certain confidence seen in parts of the field” (p. 52) either that we have it all figured out, or that we can proceed no further figuring it out. A fresh take on consciousness, Veit offers an actionable way forward to cracking this nut and has written a challenging, thought-provoking, and worthwhile book.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

A Philosophy for the Science of Animal Consciousness

Other recommended books mentioned in this review:

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