A group of prominent scientists and philosophers have published a declaration that there is evidence that a wide range of animals exhibit signs of consciousness. The document is The New York Declaration of Consciousness.¹ The declaration states, “The empirical evidence indicates at least a realistic possibility of conscious experience in all vertebrates (including reptiles, amphibians, and fishes) and many invertebrates (including, at minimum, cephalopod mollusks, decapod crustaceans, and insects).”

This document is an updated version of the 2012 Cambridge Declaration on Consciousness, which stated, “The weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Nonhuman animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates.”² The inclusion of invertebrates, particular insects, in the new declaration pushes the assertion for consciousness in animals significantly farther than most scientists have previously claimed.

Evidence For…And Against

The document is accompanied by references to a number of recent studies that provide supporting evidence. The cited evidence includes:

• Apparent avoidance of pain by octopuses.
• Animals including crabs, iguanas, and bees exhibit decision-making to avoid painful stimuli, and other tradeoff types of decisions.
• Some animals, including fish, appear to pass a version of the so-called “mirror-mark” test, which is intended to determine if the animal can recognize itself in a mirror. The test is asserted to be evidence of self-awareness. 
• Indication that some animals (including fish, tortoises, and honeybees) show signs of curiosity by seeking new information.
• Bees exhibit “play” behavior, where they roll wooden balls, which has no apparent function.
• Fruit flies exhibit sleep cycles, analogous to slow-wave and REM sleep in humans.

“What Is It Like to Be a Bat?”

It should be noted that there is no consensus scientific definition of consciousness. In fact, it has only been fairly recently that serious scientific investigation has been conducted on the question of animal consciousness. There are currently a number of proposed theories about what consciousness is. The background material includes a discussion about the definition:

What is consciousness? The term has a variety of meanings. The New York Declaration on Animal Consciousness focuses on one important meaning, sometimes called “phenomenal consciousness” or “sentience.” The question here is which animals can have subjective experiences. This can include sensory experiences (say, the experience of a particular touch, taste, sight, or smell) as well as experiences that feel good or bad (say, the experience of pleasure, pain, hope, or fear). This sense of the term “consciousness” is what Thomas Nagel had in mind when he famously asked “What is it like to be a bat?”³

It is important to be clear about terminology here. There are various types of behavior that some consider a form of consciousness. Sentience refers to an animal taking in sensory information and processing it to produce behaviors. A synonym for sentience is perception, which is defined as “The interpretation of these signals which occurs when sensory information is processed, organized, and filtered within the central nervous system.”⁴ Sentience is a phenomenon that occurs in all animals, including those with small brains such as worms and fruit flies. The New York Declaration appears to equate sentience with consciousness. That is inconsistent with the views of many scientists. 

As pointed out in Nature, “Subjective experience does not require the capacity to think about one’s experiences.”⁵ The Nature article cites the view of neuroscientist Hakwan Lau, who “acknowledges that there is a growing body of work showing sophisticated perceptual behaviour in animals, but he contends that that’s not necessarily indicative of consciousness. In humans, for example, there is both conscious and unconscious perception.” Equating sentience with subjective emotional experiences such as pleasure, pain, hope, or fear is an anthropomorphic judgment. 

Cognitive Behaviors Without Consciousness

Another important behavioral term is cognition, which is typically defined as “the mechanisms by which animals acquire, process, store, and act on information from the environment. These include perception, learning, memory, and decision-making.”⁶ Most scientists recognize that there is a difference between cognition and consciousness. Animals can exhibit cognitive behaviors without having consciousness. Psychology professors Mary Olmstead and Valerie Kuhlmeier write, “Although many may believe that animals possess complex thought processes, they recognize the difficulty of finding an objective measure of consciousness in non-verbal subjects (i.e., animals).”⁷ Insects such as bees and ants exhibit a number of complex behaviors that are innate or programmed, without involving consciousness.⁸

The New York Declaration does include a caveat:

It would be inappropriate to talk about “proof,” “certainty,” or “conclusive evidence” in the search for animal consciousness, because the nature of consciousness is still hotly contested. However, it is entirely appropriate to interpret these remarkable displays of learning, memory, planning, problem-solving, self-awareness, and other such capacities as evidence of consciousness in cases where the same behavior, if found in a human or other mammal, would be well explained by conscious processing. 

Yet here too, many scientists disagree. Simply because different animals exhibit similar behaviors is no proof that they involve the same mechanisms. For example, humans may arrive at decisions using a reasoning process, whereas some animals make decisions that use a process that is innate and does not involve the same type of human reasoning.

Firing Morgan’s Canon

Traditionally, behavioral scientists have invoked a principle called Morgan’s Canon, named for psychologist C. Lloyd Morgan. The canon states, “In no case may we interpret an action as the outcome of the existence of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale.”⁹ It is viewed as an application of Occam’s razor, which holds that “the simplest explanation is usually the best one.” While there is an ongoing debate about how to apply Morgan’s Canon, many scientists continue to believe there should be a bias toward explanations in terms of simple mechanisms. That would favor explanations of behaviors in terms of conditioning and associative learning without involving consciousness.

Another skeptic about the broad claims of animal consciousness is philosopher Peter Carruthers. He focuses his arguments on the capability for higher order awareness and thought. Carruthers states, “Philosophers and psychologists have claimed — not unreasonably — that consciousness requires capacities for higher-order thought.”¹⁰ Based on that premise, his conclusion is that, “It seems likely that there can only be higher-order awareness of one’s own mental states in a relatively small class of nonhuman creatures (perhaps only great apes, or perhaps primates more generally; or maybe extending to some other social creatures such as dolphins and elephants).” 

The last part of the New York Declaration concerns animal welfare:

When there is a realistic possibility of conscious experience in an animal, it is irresponsible to ignore that possibility in decisions affecting that animal. We should consider welfare risks and use the evidence to inform our responses to these risks.

When it comes to most mammals, there hasn’t been much controversy about the need to consider animal welfare. However, including fish and insects is likely to generate significant debate.

Notes

1. https://sites.google.com/nyu.edu/nydeclaration/declaration.
2. Low, P. “The Cambridge Declaration on Consciousness.” Proceedings of the Francis Crick Memorial Conference (Churchill College, Cambridge University, July 7, 2012), pp 1-2.
3. Andrews, K., Birch, J., Sebo, J., and Sims, T. (2024) Background to the New York Declaration on Animal Consciousness. nydeclaration.com.
4. Mary C. Olmstead and Valerie A. Kuhlmeier, Comparative Cognition (Cambridge: Cambridge University Press, 2015), p. 23.
5. Mariana Lenharo, “Do insects have an inner life? Animal consciousness needs a rethink,” Nature, April 19, 2024.
6. Sara J. Shettleworth, Cognition, Evolution, and Behavior (Oxford: Oxford University Press, 2010), p. 4.
7. Olmstead and Kuhlmeier, Comparative Cognition, p. 24.
8. Eric Cassell, Animal Algorithms (Seattle: Discovery Institute Press, 2021).
9. Sara J. Shettleworth, Cognition, Evolution, and Behavior (Oxford: Oxford University Press, 2010), p. 18.
10. Peter Carruthers, “Comparative psychology without consciousness,” Consciousness and Cognition, 63 (2018), pp. 47-60.