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Why does consciousness exist? The answer lies in the evolutionary origins of the simplest forms of subjective experience, not in studies of human consciousness alone, which represent just one special case within the animal kingdom. The need for a Darwinian bottom-up approach that reconstructs these simple origins and then successively builds more complex forms on top was a central message of my book A Philosophy for the Science of Animal Consciousness.
This may not seem controversial, but philosophers have long been hostile to the idea that evolutionary biology could resolve major philosophical problems. I therefore anticipated immediate pushback. But it did not come.
In the first 10 commentaries published in special issues on my book, scientists and philosophers alike agreed with my evolutionary approach, applying my theory to species such as elephants and macaques (more on this in a future post). I was almost disappointed, however, having prepared myself to defend the importance of evolution for understanding the mind.
Then Christian de Weerd’s commentary arrived just before the submission deadline. I had invited him because of an earlier argument he published with Leonard Dung against Darwinian approaches to consciousness. No objection could be more fundamental, of course, so I was glad to have the opportunity to respond in depth in a 15,000-word reply addressing several critics.
My journal article, titled “On the Evolution, Science, and Metaphysics of Consciousness,” was published open access this week. Here, I will summarize my arguments for a general non-specialist readership.
How We Study Consciousness Now
Walk into consciousness labs, and you will mostly find studies on humans relying on verbal reports. This evidence is then used to construct theories of consciousness and applied to special cases like chimps, octopuses, shrimps, and maybe artificial intelligence.
De Weerd admits we have expanded our toolkit to include other studies in other animals, such as great apes, but this is far from treating consciousness in a Darwinian manner. He argues we can capture markers of conscious processing in our species and then apply these tests to other animals. But consciousness may come in radically different forms in distantly related species. While I don’t deny that this approach can make progress, it remains fundamentally tied to humans. An evolutionary “bottom-up” approach shifts the focus from a “top-down” approach centred on humans to the rest of the animal kingdom.
However, de Weerd denies that this is even possible, because he thinks that an evolutionary bottom-up approach means ignoring human evidence entirely. But that is a strawman.
How We Should Study Consciousness
If we look beyond consciousness, this demand should seem obviously ludicrous. No evolutionary biologist studying, for instance, the immune system or the eye, refuses human data. Evidence from Homo sapiens sits alongside evidence from other species. That is how evolutionary biology works.
Unfortunately, consciousness science has remained fundamentally a-historical. When researchers sometimes consider its origins, they ask how and when human features of consciousness could have evolved. Imagine studying vision this way: Obsess over human retinas, build elaborate models of our colour vision, then work backward to other animals. You would miss the compound eyes of shrimp and the pinhole eyes of nautiluses, among many other strange inventions. Biology is about diversity of forms, not about a single scale toward human perfection.
Is consciousness fundamentally different from every other biological phenomenon, or have we been treating it that way for no good reason? Biology was revolutionized by Darwinian tools. Natural selection. Functional analysis. Phylogenetic thinking. These cracked open the mysteries of eyes, immune systems, and flight. Strip these tools away, and you are back in pre-Darwinian biology, which is precisely where consciousness science finds itself.
De Weerd claims my evolutionary approach lacks tools to disentangle conscious from unconscious processing without controversial assumptions. But he is mistaken. The bottom-up approach uses everything the top-down approach in addition to the tools of evolutionary biology. Facts about the origins of animals, the brain, and ancestral lifestyles provide constraints and provide evidence to evaluate which theories make sense.
Theories built around uniquely human capacities (such as complex language, meta-cognition, and self-awareness) mistake what makes us distinctive for what makes consciousness possible. This is why I proposed the pathological complexity thesis: Consciousness evolved to help organisms with complex bodies navigate difficult trade-offs. The origins of consciousness were simple evaluative feelings, good and bad, signalling what to do.
De Weerd also objects that evolutionary reasoning is too speculative. But this worry just highlights how consciousness science has put itself in a straitjacket. The top-down approach has insulated consciousness research from the very tools that revolutionized our understanding of all other biological phenomena. Admittedly, that was not entirely unreasonable, at least initially. Consciousness research long struggled for legitimacy. To make it appear as objective as possible, they minimized all speculation. But not all speculation is unscientific. All scientific work on the deep past has to deal with sparse evidence. But you simply build competing models, gather evidence, and refine theories. This is empirically grounded and entirely justified “speculation.”
What is unjustified speculation, however, is the assumption that consciousness should be treated differently than all other biological phenomena.
I am advocating a Darwinian revolution, not because mainstream approaches must fail at understanding human consciousness but because they will distort our picture of consciousness as a natural phenomenon spanning millions of species across millions of years. To understand octopus minds, crow minds, shrimp minds, and the first conscious creatures, we need to treat consciousness as an evolved biological adaptation solving specific ecological problems for different kinds of species.
