Behaviors of crows, chimpanzees, elephants, and many other birds and mammals suggest they may have "consciousness."
However, the list doesn't stop at vertebrates, as researchers are expanding consciousness studies to include a wider range of animals, including octopuses, and even bees and flies.
According to Nature, based on this ongoing expansion of research, a coalition of scientists is calling for a reevaluation of the relationship between animals and humans. Last month, dozens of scientists from various fields jointly signed the "New York Declaration on Animal Consciousness," aiming to promote more research and funding support for animal consciousness.
Jonathan Birch, a philosopher at the London School of Economics and one of the authors of the declaration, stated that with accumulating evidence, scientists are taking this topic seriously rather than dismissing it as a crazy idea as in the past.
The declaration points out that ignoring the possibility of conscious experiences in animals when making decisions that affect them is irresponsible.
However, the declaration does not provide a definitive answer on which species definitely have conscious experiences. It indicates there is enough evidence to suggest a real possibility of conscious experiences in species vastly different from humans, such as reptiles, fish, insects, and other animals traditionally not thought to have mental lives, while birds and mammals have strong scientific support for their consciousness.
Birch mentioned that consciousness is complex to define, but their research group focuses on one aspect of consciousness, which is perception. This is often defined as the capacity for subjective experience. For animals, this experience includes smelling, tasting, hearing, or touching the world around them, as well as feeling fear, joy, or pain. However, subjective experience does not necessarily require the ability to reflect on one's experiences.
"Since non-human animals cannot express their inner states through language, scientists typically rely on indirect evidence to assess consciousness in these animals, looking for certain behaviors associated with conscious experiences," Birch said.
One classic experiment is the "mirror test," a test of self-awareness to see if animals can recognize themselves in a mirror. In this experiment, scientists place stickers or other visual markers on animals and observe their reactions in front of a mirror. Some animals, including chimpanzees, Asian elephants, and cleaner fish, show curiosity towards the marks, even attempting to remove them. This behavior suggests they may have self-awareness, which could be a sign of conscious experience.
Experiments on crows, octopuses, and others also indicate some of their behaviors as potential signs of conscious experiences.
Additionally, a study on fruit flies showed they have both deep sleep and active sleep. In active sleep, the brain activity of fruit flies is similar to when they are awake.
"This might be similar to rapid eye movement sleep in humans, where the most vivid dreams occur. We interpret this as a conscious experience," said Bruno van Swinderen, a biologist at the University of Queensland studying fruit fly behavior, who signed the declaration. Some believe dreams are a key component of consciousness, so if flies and other invertebrates have active sleep, it could be a good clue that they may have consciousness.
However, some researchers remain skeptical of existing evidence on animal consciousness. "I think there's basically no decisive evidence so far," said Hakwan Lau, a neuroscientist at the RIKEN Center for Brain Science in Japan. While more studies show animals have complex perceptual behaviors, it doesn't necessarily mean they are conscious. For example, in humans, there are both conscious and unconscious perceptions.
Nevertheless, some researchers suggest that even without a clear answer, the declaration could still have a positive impact on shaping policies related to animal ethics and welfare.
