Zebrafish can recognise their reflection in a mirror. Bees play with wooden balls, apparently for fun. eat less lunch when they anticipate a more delicious dinner. These recent discoveries were presented as mounting evidence that species across the animal kingdom have the capacity for consciousness. The findings have come piecemeal over decades, as researchers study one species or another. But taking a look at them together prompted a group of around 40 scientists to sign at a conference on 19 April.
The declaration calls for formal acknowledgement that conscious experiences are had by an incredible range of animals, stating that there is 鈥渟trong scientific support for attributions of conscious experience鈥� in mammals and birds and 鈥渁t least a realistic possibility of conscious experience鈥� in fish, amphibians, reptiles and many invertebrates, such as molluscs, crustaceans and insects.
This is an enormous claim, and one that is by no means agreed upon by all scientists. For one thing, there is no widely accepted definition of consciousness. The declaration defines consciousness as sentience, which includes sensory experiences such as taste, touch and smell. It also asserts that animals can have good and bad experiences, including hope, pain or fear.
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Decades of research support the idea that highly intelligent animals like chimpanzees and crows display evidence of consciousness: they learn language, use tools and have complex social structures. However, it is challenging for researchers to test the theory in species that may show less obvious signs of consciousness.
A series of studies have found that cleaner wrasse, for example, seem to pass the mirror-mark test, which scientists often use to see if an animal recognises its reflection in a mirror as its own body 鈥� a potential indicator of consciousness. Garter snakes passed a scent-based version of the test. But whether this signals a conscious experience is still very much under debate.
When it comes to invertebrates, the evidence is far less robust, but it is growing. A 2020 study of cuttlefish found that the cephalopods could recall past events, including what happened, when and where. A study the following year found octopuses avoid pain and seek pain-relieving treatments. Nervous crayfish calm down when given benzodiazepines, medications used to alleviate anxiety in humans, according to a series of studies on the animals. But whether these suggest something akin to a conscious experience depends very much on how you define consciousness.
鈥淚 agree with much of the declaration, but not that there is a real possibility of insect consciousness,鈥� says at New York University. Block says the risk to such a declaration is that it might sway how objectively scientists approach their investigation of consciousness in animals.
For example, evidence that bees play could clue us into their cognitive abilities and motivations but doesn鈥檛 necessarily rise to the level of a conscious experience. 鈥淚t is only by hearing opponents that one can objectively evaluate whether one has neglected relevant evidence or taken flawed evidence too seriously,鈥� says Block.
Another issue is that experiments probing consciousness often frame it in human terms, leaving some creatures and abilities overlooked. 鈥淚t seems unlikely that the kind of consciousness that reptiles have is similar to the types of consciousness that humans have,鈥� said at Wilfrid Laurier University in Ontario, Canada, at the conference. But he said that doesn鈥檛 rule it out. 鈥淲e shouldn鈥檛 expect their consciousness to look anything like ours,鈥� said Miller.
Because there may be indicators of consciousness that don鈥檛 relate at all to the human experience, scientists will need to re-think how they probe if an animal has the capacity for consciousness. And the signers of the declaration are calling for more research. But, to some in the field, these signatories have jumped the gun on claiming that a bee or a shrimp experience consciousness, particularly as we have a limited set of tools with which to answer such a question.
