Possums and the Evolution of Consciousness
What a nocturnal animal can teach us about the origins of consciousness.
Updated January 19, 2026 | Reviewed by Ekua Hagan
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It is 3 a.m., and I am awake in Australia, my body stubbornly refusing to adjust to the time zone difference. Suddenly, a lot of noise starts coming from the outside. I look out of one of the windows and spot the source: a young common brushtail possum. Unless you are Australian or have been to Australia before, I suspect you have never heard of or even seen this species. That is one of the reasons I used them in my book, A Philosophy for the Science of Animal Consciousness , as an illustration for why consciousness exists in the animal kingdom.
Picture a possum foraging for food somewhere out in the bush under the cover of night. Somewhere nearby, fledgling birds chirp from an unguarded nest. For the possum, this is an opportunity made audible: protein, calories, survival. But opportunities come with risks. While the possum investigates, it could itself become prey. A dingo might emerge from the shadows. A powerful owl might swoop down in silence. A single moment of distraction could end its life.
Now place yourself in the possum’s "shoes."
Do you hide, or do you try to find food in exposed areas? Where do you go to forage? How much time do you spend in one area? These decisions are far from simple. And they are not rare edge cases, either. Every moment, animals face difficult trade-offs. They are the daily texture of life. How do animals solve these problems?
The answer I developed in my book is that consciousness evolved precisely to handle these pathological complexity trade-offs, having to carefully balance risks to their survival and reproduction. Making the wrong decision is no less pathological than failing to fight off an infection. All organisms strive towards their optimal healthy behaviour (even if this falls short of enjoying eternal life with infinite offspring). All species, whether possums or shrimp, have different strategies to maximize their fitness. And consciousness helps a subset of these species to deal with very complex ones.
By "consciousness," I am not referring to human consciousness with all its idiosyncrasies, such as self-awareness and mental time travel. At the evolutionary origins of consciousness, we see something simpler and more fundamental: the ability to have positive and negative experiences. Pleasure and pain. Attraction and aversion. What philosophers call "hedonic affect," and what the rest of us call feelings. This is the pathological complexity thesis: Consciousness originally emerged in the form of simple evaluative feelings to enable animals to deal with complex strategies that involve complex trade-offs.
Recently, I published an article summarizing the main claims of my book for a special issue inviting comments. In my previous post, I summarized my response to one commenter who argued against the possibility of trying to understand consciousness from an evolutionary perspective. Here, instead of continuing that back-and-forth with the others, I want to step back and offer a brief synopsis of when and how I think consciousness emerged that is accessible to a non-specialist audience.
When did consciousness emerge?
In my book, I date the origins of consciousness back to the Cambrian explosion about 540 million years ago. Before that, animal life was largely sessile, like the stationary filter feeders we still see today. The explosion brought about a great diversity of new shapes of animals, most of which went extinct, but there was one crucial innovation : the ability to control a complex body.
Once animals evolved appendages and the ability to explore the world with them, they were faced with a large range of options, but constrained by bodies that could only engage in one action at a time. This explosion in bodily complexity brought about an explosion in decision-making complexity, not unlike the problems faced by our cute possums today. For evolution to unlock this new design space, exploring a vast new range of alternative body plans required the means for controlling such a system. The solution, I argue, was consciousness.
Pleasure, pain, and the origin of consciousness
The neuroscientist Michel Cabanac (1992) proposed that pleasure provides a "common currency" for decision-making. Just like money lets you compare apples and oranges by converting both into dollars, hedonic feelings do something similar: They convert different types of value (food, safety, mating, rest) into a single scale of better and worse. This enables animals to make decisions in line with the ultimate currency of biology: fitness (that is, survival and reproduction). This is not just a metaphor. The brain needs an actual mechanism to compare incompatible ends.
As the biologists David McFarland and Richard Sibly put it (Cabanac, 1992):
“[D]ecisions among different courses of action must be made in terms of a common currency, and weighted among a common set of criteria. The necessity for comparing the merits of different courses of action implies that there must be some “trade-off” mechanism built into the motivational control system. Since the trade-off process must take into account all relevant motivational variables, it is clear that the mechanism responsible must be located at a point of convergence in the motivational organization.”
Complex bodies are costly investments. Not just in terms of resources, but much more in terms of resource management . Acquiring capital for a start-up is easy compared to the difficulty of successfully running it.
Once evolution hit on hedonic evaluations as a solution for how to manage agency of this kind, even more complex bodies became manageable. From there, further elaborations followed. Sensory experience enriched what could be evaluated. Self-other distinctions grew out of separating internal signals from external events. The more familiar features of human consciousness emerged later, unevenly, and only in some lineages.
As I watch the possum feel its way through the night, navigating a world of risks and rewards, I believe it naturally follows that dealing with this complexity is what its consciousness is for. If we study their world more closely, we are offered a window into what it is like to be them.
Veit, W. (2024). The role of consciousness in adaptive behaviour: A philosophy for the science of animal consciousness. Adaptive Behavior . https://doi.org/10.1177/10597123241293184
Cabanac M. Pleasure: the common currency. J Theor Biol. 1992 Mar 21;155(2):173-200. doi: 10.1016/s0022-5193(05)80594-6. PMID: 12240693.
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Walter Veit, Ph.D., is a lecturer in philosophy at the University of Reading.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.