There are two questions regarding animal consciousness: “Which animals are conscious?” and “How are animals conscious?” Given increased attention to the experiences of invertebrates such as cephalopods, insects, and crustaceans, this article delves into the first question, making the case that it’s actually the second question that reveals more about what matters to animals.

Investigating Animal Consciousness

The common methods that researchers use to determine which animals are likely to be conscious fall into two schools of thought. The first involves using theories of consciousness. However, according to the author, this method has major issues related to the theories themselves. Because they’re based on the idea that human consciousness is the only case example, they exclude most animals more distantly related to humans.

The second method tries to find observable features — markers of consciousness — instead of defining consciousness itself. While this is considered best practice, the author believes that it leads to bias towards more highly developed animals rather than equally applying to all animals. In its current use, the marker method only reinforces the consciousness of animals who humans have decided are worth looking into further.

Therefore, the author suggests developing a new theory of consciousness based on the idea that all animals are conscious.

An Example Of The Marker Method

The author cites a hallmark review of the evidence of sentience in cephalopods and crustaceans as a case study of the marker method’s use. Sentience can be considered as one kind of consciousness.

The review uses pain-related behaviors and biological structures as markers, concluding that there’s very strong evidence of sentience in octopuses and strong evidence of sentience in true crabs. Applying these same markers to Caenorhabditis elegans, a type of nematode with fewer than 350 neurons, the author suggests that there’s substantial evidence of sentience in these simple animals as well. However, as nematodes have long been presumed to be unconscious, this raises the question of whether the marker system can accurately be used to measure animal consciousness.

Markers Can Be A Slippery Slope

Next, the author goes on to discuss how markers of consciousness are used to find other markers of consciousness and, together, these marker “clusters” increase confidence in an animal’s consciousness. For example, markers of happiness like smiling and laughing in humans are linked to the ultrasonic laugh-like chirps in rats that are thought to indicate a similar emotion. Likewise, the brain chemical oxytocin, which is associated with social bonding and learning in humans, has a correlate in Caenorhabditis elegans. These nematodes possess nemotocin, a neuropeptide that’s involved in learning and mating — thus suggesting similar functions in very distantly related species.

For the author, this reinforces their issue with the marker system: that it doesn’t really provide a cutoff of consciousness within the animal kingdom.

Using Markers To Answer The “How” Rather Than The “Who”

According to the author, a lack of markers of consciousness doesn’t necessarily mean that an animal is unconscious either. Negative markers, such as lacking a central nervous system or possessing too few neurons, rest on the assumption that we know what kind of neurobiology is necessary for consciousness, which we don’t.

Meanwhile, new research on animal biology is constantly occurring. There’s a strong possibility that a marker of consciousness will be discovered that will implicate more and more of the animal kingdom until all animals are included in it.

Oftentimes, researchers will dismiss markers of consciousness that show up in simpler animals like Caenorhabditis elegans who’ve been deemed unconscious. However, the author points to the fact that one of the most classic markers, the ability to hold a conversation, is practiced by an unconscious entity now: large language models. This doesn’t make the marker of language invalid, but rather highlights the need for other markers of consciousness to be present.

Due to the fact that there are no negative markers and new markers are constantly being discovered, and the idea that older markers tend to be downgraded rather than discarded as new discoveries are made, the author argues that all animals can be found to be sentient through the marker system, regardless of how simple or complex they are.

Thus, they believe that markers are far more useful in telling us about an animal’s experience of consciousness than whether or not they’re conscious.

Finally, the author concludes their argument for why all animals should be considered conscious by highlighting the potential ethical concerns of assuming that they aren’t. Beyond introducing bias and reducing the quality of scientific research, doing so ignores animals’ needs and wants, limits our understanding of them, and ultimately impacts how we treat them. When we assume that all animals are conscious by default, the focus of the consciousness question can then shift from the who to the how.