Foundations of Animal Consciousness

When a banana harvesting machine detects and grabs a banana, there is nothing it’s like to be that machine. The machine does not have a point of view or a stream of consciousness. But when a human or monkey looks a banana, there is something it’s like for us to see it. Qualities of the fruit’s shape, size, and color manifest in our stream of consciousness. If we grasp the object, we can feel its texture and firmness. And if we bite into the banana, we can taste its sweetness. Most agree that primates are not the only kinds of creatures that have experiences like taste, smell, sight, touch, sounds, pleasure and pain. But it can be difficult to sort out which other creatures do, as well as the qualities that decorate their inner worlds. Do worms have any experiences or are they like the banana harvesting machine? Do wasps experience pain when sprayed with Raid? Do fish experience fear or sadness? And what should we say about octopuses?  

You might ask, “how we could possibly know what’s going on inside another creature’s head?!” There’s no way to peek inside to see their thoughts or emotions. What if all nonhuman creatures are mindless machines? The 17^th century philosopher Rene Descartes thought that animals were complex automata that God designed for us to use, programmed to react to stimuli without ever feeling or thinking anything. Humans are special, says Descartes, because we are immaterial souls created by God to exercise free control over our bodies. While we can’t definitively say he is wrong, Descartes’s views about animal minds are now extremely controversial, even among theists. But why exactly do most philosophers today reject Descartes’s views about animals? Part of the story is that we’ve learned a lot more about animal behavior, the brain, and the evolution of life on Earth. The other part of the story involves reasoning from this newly acquired knowledge to the existence of animal minds. Conceptual tools like analogical inferences and inferences to the best explanation can be used to build bridges between our observations of the world and our theories. Before judging the reasons philosophers have for thinking some animals have minds, it’s useful to first review the reasons for thinking that other people have minds.

How do you know that you aren’t alone in this world? It’s possible that all other humans that you interact with are like the banana harvesting machine but behave like they have minds. How could that be? Perhaps you are in a perfect computer simulation and those around you are all mindless NPCs. Or maybe your mind has just been spontaneously created by a freak natural accident with false memories of a past and you’re currently dreaming all of this up. It’s impossible to conclusively disprove either of these scenarios using observations, however unlikely we take them to be. Any form of evidence against either hypothesis could be understood as part of a well-designed simulation or a vivid dream. So, if we’re going to discount the possibility of knowing about other nonhuman minds, on the grounds that it’s possible Descartes is right, we must also say the same about the minds of our family and friends. I don’t think we need to conclusively rule out these radical skeptical scenarios to justifiably believe there are other minds. But what then justifies our beliefs about other minds?

There are many similarities that I can observe between me and other humans. Typically, other humans make eye contact during conversation and can infer the kind of mood I’m in. They can answer questions about what’s on their mind, they scream when they stub their toes and sometimes will laugh at my jokes. They also have similar brains and perceptual organs to my own, not created by a mad scientist, but are products of evolution by natural selection. If other humans behave in consistently similar ways to me across a wide range of contexts, are neurobiologically very similar, and have an evolutionary history, then they (probably) have a mind like I do. The inference from my own mind to other humans is not airtight, but it’s the nearly as strong as can be. The only stronger inference to other minds would involve my perfect clone.  

Applying this inference to creatures outside our species gets trickier. Nonhumans often exhibit different behaviors, vary in their neuroanatomy, and have different evolutionary histories. But still, the inference remains very strong for at least some groupings of creatures. Nonhuman apes like chimpanzees exhibit many of the same behaviors as us, have a complex brain with a neocortex, and they are evolutionarily closely related to us. The common ancestor between chimpanzees and humans can be traced back to around six million years ago, which in evolutionary time is not very long ago. Chimpanzees exhibit complex and flexible behaviors that are best explained by the presence of psychological capacities such as self-awareness, episodic memory and foresight, as well as logical and mathematical reasoning. If we can be at least 99% sure other humans have minds, we can be at least 98% sure chimpanzees do too.

The common ancestor of all mammals lived around 180 million years ago. The timescale is grand enough for some mammals to have evolved significantly different behavioral and neuroanatomical traits, but no such examples have (yet) been discovered. All mammals have the same basic structure including the possession of a neocortex found in us and chimpanzees. So, generalizing this analogical inference to all mammals is also well justified.

When around other mammals, many just find it obvious that they have minds like we do. It’s especially true when considering cats and dogs. We often attribute a wide range of mental states to them without much deliberation. Most people who attribute mental states to their pets don’t know much about the brain or evolutionary theory but clearly recognize the many behavioral similarities between us and them. Certain observed behaviors cry out for an explanation and the possession of a mind seems like the best one. When a cat screams after its owner steps on its tail, we infer that the cat is in pain. When a cat meows after long periods without food, we infer that they are hungry. And when a cat runs away from helium balloons or cucumbers, we infer that they saw the object and are afraid of it. As a cat owner, I could spend all day listing examples.

We, in principle, could learn something about cats, chimpanzees, or other humans that casts serious doubt upon the existence of their minds. We could in the process of doing brain surgery, we discover that other humans have hard drives in their skulls. Or maybe we are approached by men in black suits who provide ample evidence that this world is a computer simulation. Perhaps Descartes is right about animals and God informs us through an act of revelation. But merely imagining ways that others may not have minds, given all the evidence to the contrary, does not create a reasonable doubt.

In surveying other groupings of animals, we’ll encounter some potentially relevant differences. As we will see, it is more difficult to justifiably infer the existence of animal consciousness outside of our mammalian class, and in some cases, it will make sense to deny mentality to some of these other groupings. In the next post of this series, I will evaluate the prospects for four non-mammalian animal groupings: annelids, bivalves, cnidarians, and gastropods. Do earthworms feel pain when hooked? Can clams feel the steam rising from a cooking pan? Is there something it’s like for jellyfish see or smell bioluminescence? Do sea slugs fear their predators?