Peter Singer On How To Live An Ethical Life
There are gradations of certainty about animal suffering. It’s very clear that chimps feel pain, and equally clear that plants don’t. We can say with reasonable confidence that all vertebrates suffer, because they respond to stimuli in the same way that humans do when we are in pain. With invertebrates, it’s harder to know, although certainly they can be intelligent. Octopuses, for example, have shown remarkable abilities to solve novel problems. So I assume they are conscious and therefore can suffer.