You might find yourself one day in a restaurant with friends and, feeling a little adventurous, you order a plate of fried octopus. The plate looks colourful, elegant and appetising. You dig in. The conversation turns to ethical issues around food – the journey it takes from the farm to your mouth, the conditions of developing world workers who might have fished for the food and so on. Then the topic of animal suffering turns up. One friend points out that the octopus has half a billion neurons, about as much as your beloved pet cat. Does this make you stop eating your dish? Should it? Issues like carbon emissions can be calculated, but it seems there’s no equivalent quantifiable measure to do the same for animal suffering. And how can we even know that the animal is in distress in the first place?
The ethical stakes
Whether animals are conscious or not is a big deal. A billion tonnes of food derived from animals is produced each year, much of it via intensive farming. Many millions of animal experiments are carried out annually as well, including on primates. If no other species aside from humans is conscious, it doesn’t matter, because to experience suffering requires consciousness. However, if all the animals we potentially exploit for the food chain and for research had an extensive consciousness, and were suffering in ways similar to us, then the ethical implications would be vast.
So how do we even make any scientific progress on this problem? In humans we can simply ask each other about experiences, and therefore use language as solid evidence for consciousness. With the possible exception of a handful of lab-trained great apes, we lack this key evidence in all other species. Instead, we need another route.
One way to start is to take some behaviour that we know reflects consciousness in humans, and see if any other species show the same behaviour. This is indeed a useful approach, but unless we’re cautious it can lead to assuming other animals are both more and less conscious than they might actually be.
For instance, consider pain. If I accidentally touch a heated pot while cooking, a reflex action will cause my hand to quickly withdraw, and I might do a fair bit of screaming as well, before I actually experience any sensation of pain. Pretty much all species will also withdraw to unpleasant stimuli, so the reflex doesn’t in any way imply suffering. But I might also spend a good portion of the next few minutes rubbing my burnt hand, because it is really persistently painful! How many other species show a similar prolonged response? Quite a few! Even the humble prawn belongs to this club :
If you apply a noxious substance, such as an acid, to a prawn antenna, it will keep rubbing at this for 5 minutes, significantly more times than the untouched antenna on the other side, or if that antenna has a local anaesthetic applied. Does this mean that the prawn was actually feeling the pain and thus was demonstrating consciousness? That’s one possible explanation, but it isn’t the only one. For instance, the prawn’s sustained behaviour might also be an unconscious reflex to some continuous sensory input from its antenna, perhaps with the instinctive purpose to clear it of some particle persistently stuck to the appendage.
Many species have similar neural machinery to process pain as we do, and demonstrate adaptable behaviour to a noxious substance, such as rapidly learning to avoid the source of pain. A surprisingly broad range of species will even pay some cost to get access to pain-reducing drugs. For instance, zebrafish will move towards a previously fearful environment if they have been injected with a noxious substance and that environment is infused with an analgesic .
All these complex behaviours are tentatively suggestive that these animals actually suffer, and perhaps ethically we should err on the side of caution and assume this is true. But again, scientifically, we have to acknowledge other, non-conscious, alternatives. Always, we should ask ourselves whether a simple artificial intelligence robot could be trained to generate the same kind of pain-learning-based behaviour as some animal, with no consciousness whatsoever .
We also have the opposite problem of intuition when animals behave in ways that might suggest a lack of consciousness or suffering to us, but inside their minds they might have a very advanced form of consciousness – just one we can’t observe. Let’s say we devise some test of consciousness, and some species fails this test. Maybe that means it isn’t capable of consciousness. Or it means the animal isn’t interested in the stimuli, isn’t motivated to jump through the hoops of our particular test, or we’ve designed the experiment in a chauvinistic way, not accounting for the sensory differences between humans and other species. In short, a failure on any such test would not demonstrate a lack of consciousness or suffering, for a range of possible alternative reasons.
Looking at the animal in the mirror
So what specific examples do we have where we know some behaviour is conscious in humans, and we have observed it in other species? The most famous example is recognising oneself in a mirror, which doesn’t just demonstrate consciousness, but a high form of consciousness, that of self-awareness. In the lab this can be tested by applying a mark on the animal’s face in a way that is usually invisible to them, but becomes visible when they view themselves in a mirror. If they recognise what they see as themselves, then they might try to remove this strange facial mark.
What other species pass this test? The list includes the great apes , monkeys , dolphins , and possibly also elephants . Perhaps most surprising of all, one study has demonstrated that magpies can also recognise themselves in a mirror .
It is a reasonable assumption, therefore, that at least these species are conscious. I should emphasise again, though, that if a species doesn’t pass this test, we certainly can’t infer that they lack self-awareness, and over time, it’s highly likely that the above list of those species that can recognise themselves in a mirror will steadily grow.
Another form of advanced consciousness in humans is metacognition, which is our ability to know the extent and limits of our own knowledge. Sometimes we’re very confident that we saw or remembered something accurately, and at other times we’re simply not sure. We can test this in other species by giving them something challenging to learn, such as a particular sequence of four pictures. Sometimes if they’re stuck, they can press a button to get a hint as to the next picture to choose, but doing this leads to a less desirable reward (a boring banana pellet), compared to getting the sequence correct without asking for a hint (a lovely sweet M & M). If we were doing this task, we’d ask for hints at the beginning when we’re learning the sequence, then not use them once we know the sequence, to get the more exciting reward. And that’s exactly what monkeys do as well . Great apes show metacognitive skills too , and there is even evidence that rats have this ability . Can we have unconscious metacognitive ability? In humans we would say no. In other species unconscious metacognition is highly unlikely, but possible. However, taken together with the mirror self-recognition evidence, there’s a very good case for primates to be classed as conscious, and many other mammals should be considered possibly conscious, given that rats show metacognitive ability.
What would be ideal, given that animals that fail such tests tell us very little, would be some indirect measure of consciousness in other species. We have a reasonable idea of what brain areas correspond most closely to consciousness in humans. We need the thalamus, an information relay station in the middle of the brain, to enable consciousness in the first place, but the most general-purpose parts of cortex, in the lateral prefrontal cortex, and posterior parietal cortex, which activate whenever we’re performing a novel or complex task, are also closely associated with consciousness . So what other species share these brain regions with us? As you can probably guess, our great ape cousins have very similar brain structures to humans, followed by the primates generally, but many clever mammals, including the elephants and dolphins, also have extensive versions of analogous regions. So we might want to conclude that there’s a sliding scale of consciousness based on some similarity index between humans and other species, based just on these key consciousness-related brain regions. And perhaps there’s some mileage in this approach if it also includes brain size relative to body size, and is just restricted to mammals.
But such an approach might be another form of chauvinism, discounting the possibility that brain structures distinctly different from the vertebrate blueprint could give rise to consciousness. Let me return to the octopus at the start of this article as a fascinating example. The octopus has neither a thalamus, nor any cortex to speak of, but that doesn’t mean its brain is puny. On the contrary, the common octopus has a highly advanced nervous system, even if it’s radically different to ours, with the majority of its neurons in its limbs. In line with this, it demonstrates highly intelligent, adaptable behaviour. Octopuses can learn just by observing the behaviour of others, and are inveterate problem solvers.
Does this mean they are conscious, because they are so clever? Those animals that pass the mirror self-recognition test tend also to be the smartest animals around, aside from us. Is this because of some close connection between consciousness and intelligence? I believe so, but I also have to acknowledge the possibility that such a circumstantial connection might just mean that you need sufficient intelligence to pass such tests, whereas many other species who are less intelligent may nevertheless have self-awareness, just not in a way that they can show to us in such experiments.
Whether the octopus is conscious or not, the existence of a clever “alien” like the octopus, should teach us caution in extrapolating too aggressively from our own perspective.
Another indirect attempt to explore animal consciousness is to make more general assumptions about how the human brain generates consciousness. Integrated Information Theory (IIT) is perhaps the most popular current neuroscience-inspired theory of consciousness . IIT equates consciousness with a certain combinatorial kind of information – that’s just what consciousness is, according to the theory. IIT also posits that consciousness requires a certain kind of network shape, which parts of the human brain have, but which standard computers don’t, though there’s no reason in principle why silicon networks of the right type couldn’t in the future support consciousness under IIT. IIT allows, in theory at least, for the calculation of the amount of consciousness that some being has.
Immediately we run into problems here, though, since the calculations for anything but the simplest of creatures would take billions of years to run, and we’d need to have a very accurate recording of the animal’s brain network to even attempt this anyway. These are real problems, but alternative versions are being developed that will make the calculations practicable, and similarly, with sufficient anatomical study, we could make a good approximate guess of any brain’s network. We won’t have precise answers, but a decent guess might be good enough to make progress in understanding the extent of animal consciousness for any given species.
Assuming for the moment that we can know the network architecture of some animal brain in sufficient detail, and that a version of IIT is calculable, we could then generate a number, for that species, to quantify how conscious it is. In time this would lead to a continuum of consciousness between species, presumably with humans at the top. However, even for an animal with just a handful of neurons, there would be some small level of consciousness.
IIT is a controversial theory, which has its detractors (including me; for a discussion on its problems, see here), but there are now many empirical studies that have shown that informational levels in human brain-scans distinguish conscious states, for instance, being awake vs. being in a dreamless sleep . Such empirical studies have also worked just as well in the rat brain , providing further indirect evidence that consciousness might indeed be the continuum that IIT suggests.
Being on the safe side
The bottom line is that we have a series of clues to suggest that at least some mammals, and the occasional particularly clever bird species, have capacities that in humans we’d categorically state reflects consciousness. And there is a rapidly growing literature that links consciousness with information levels in the brain, which in turn would suggest that there is a continuum of consciousness throughout the animal kingdom. Some researchers have argued that consciousness has an evolutionary advantage, because it provides the foundation for adaptable behaviour . If consciousness does indeed confer an evolutionary advantage then, from an evolutionary viewpoint, it does not make sense to propose consciousness to suddenly arise out of the blue (i.e. in the human brain) without any simpler precursor forms.
But nothing here is definitive as yet, because we simply don’t know enough about human consciousness – so far. My view, though, is that the evidence is already strong enough for us to make informed ethical decisions. The notion that the subjective experience of pain or distress is not restricted to vertebrate species is also increasingly appreciated by politics. As of 1st of January 2013, the directive of the European Union on the protection of animals for scientific purposes is in effect and it explicitly includes octopuses (2010/63/EU). And since 1st of March 2018 a new animal protection law in Switzerland bans the boiling of lobsters and other crustaceans alive, or at least requires the animals to be stunned before they are put into the pot.
Animal research for scientific advance is a tricky ethical question. I personally don’t experiment on animals, but I know that much scientific progress is made because of this. That progress could, in the long-term, benefit both human and non-humans with the medical advances discovered, which makes the question of its morality complex and nuanced.
I think the case is a lot more clear-cut when it comes to factory farming. For me personally, given that I can live just as well without animal products in my diet, and that there’s a good chance that mammals especially, but possibly almost all animal species, are conscious and might suffer, it makes sense to become vegan. And I know of a few prominent researchers in the field (Christof Koch, Nicola Clayton) who have come to similar conclusions.
So what about that octopus? It might not share my brain structures, my evolutionary history, nor my habitat, but the provisional evidence for close cognitive similarities in intelligence, play, and a host of other mental features makes me choose to err on the side of caution, so I won’t be eating any fried octopus anytime soon. That way I don’t contribute to the suffering of another possibly advanced form of consciousness.