Peter Singer is a philosopher who has argued that animals have been immorally exploited by human beings. He claims that they have, as sentient beings, certain rights, and that cruelty to animals, including their exploitation for research, food, and other means, is a violation of these rights. In some ways, this is an extension of his ethical approach to issues of poverty and privation, which he argues that the affluent have a duty to do their best to remedy. He recognizes that animals do not have the same rights as people, because they lack the rational faculties of human beings, but asserts in an essay entitled "All Animals are Equal" that:
The extension of the basic principle of equality from one group to another does not imply that we must treat both groups in exactly the same way, or grant exactly the same rights to both groups.
In other words, the fact that we do not, indeed cannot, extend certain rights to animals does not justify their exploitation. For Singer, the question that should drive human treatment of animals is not "Do they reason?" but, following a line of utilitarian thought that stems from Jeremy Bentham, "Do they suffer?" Because animals do suffer, it follows that, according to Singer, that they have an interest that humans are morally bound to respect, i.e. to avoid suffering. This principle is at the heart of Singer's theory of ethics as it relates to animals.