> I feel like it's the opposite - that, historically, many people (regardless of profession) always generally assumed that certain living things did not feel pa

> I feel like it's the opposite - that, historically, many people (regardless of profession) always generally assumed that certain living things did not feel pain or otherwise suffer for some definition of suffering. I'm not sure that's the case. Most people believe dogs feel pain by observing them, for example. Indeed, it is the most immediate common sense conclusion one can make based on observation. It wasn't until modern philosophy, specifically Descartes, characterized animals as zombie meat machines (pure res extensa). Aristotle, by contrast, did not deny non-human animals sensation or pain, as is evident in De Anima in which he reasons that sensation is in fact necessary for animals (this occurs in the context of determining the necessary faculties entailed by the nutritive soul, the sensitive soul, and the intellectual soul).