The question of whether animals other than humans can think and feel has been debated for centuries. Most of us would agree that humans have a level of consciousness, loosely defined as an ability to experience thoughts and emotions. But which other creatures have consciousness remains an open and controversial question.
We can also ask whether there are different degrees of consciousness and whether the experiences of other organisms are similar to our own. Many may think that dolphins and deer have the ability to feel emotions, but what about a fish, a bug or a plant?
Which brings us to another key question for scientists: how do we figure out if animals or plants feel? My colleagues and I recently carried out research that looks at one way of answering this question, and found that fish appear more likely to experience emotions that we previously thought.
Scientists have used many different criteria to argue for or against the proposition that non-human animals have the capacity for emotions and consciousness. Those arguing that fish, for example, do not have this capacity point out that their brains are relatively small and simple, and lack the cerebral cortex that mediates much high-level information processing in mammals.
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