Definition and viewpoints
Man beating a chained pitbull terrier
with a strap. The strap is visible in the foreground.
Throughout history, humans believed in a God-given right to treat nonhuman animals with cruelty; however, some individuals, like Leonardo da Vinci for example, who once purchased caged birds in order to set them free, were concerned. His notebooks also record his anger with the fact that humans used their dominance to raise animals for slaughter. According to contemporary philosopher Nigel Warburton, for most of human history the dominant view has been that animals are there for humans to do with as they see fit.
René Descartes believed that non-humans are automata — complex machines with no soul, mind, or reason. In Cartesian dualism, consciousness was unique to human among all other animals and linked to physical matter by divine grace. However, close analysis shows that many human features such as complex sign usage, tool use, and self-consciousness can be found in some animals.
Charles Darwin, by presenting the theory of evolution, revolutionized the way that humans viewed their relationship with other species. Darwin believed that not only did human beings have a direct kinship with other animals, but the latter had social, mental and moral lives too. Later, in The Descent of Man (1871), he wrote: "There is no fundamental difference between man and the higher mammals in their mental faculties."
Some philosophers and intellectuals, such as Peter Singer and Tom Regan, have argued that animals' ability to feel pain as humans do makes their well-being worthy of equal consideration. There are many precursors of this train of thought. Jeremy Bentham, the founder of utilitarianism, famously wrote in his An Introduction to the Principles of Morals and Legislation (1789):
The question is not, can they reason nor can they talk? but, can they suffer?
These arguments have prompted some to suggest that animals' well-being should enter a social welfare function directly, not just indirectly via its effect only on human well-being. In one survey of United States homeowners, 68% of respondents said they actually consider the price of meat a more important issue.