animal rights, moral or legal entitlements attributed to nonhuman animals, usually because of the complexity of their cognitive, emotional, and social lives or their capacity to experience physical or emotional pain or pleasure. Historically, different views of the scope of animal rights have reflected philosophical and legal developments, scientific conceptions of animal and human nature, and religious and ethical conceptions of the proper relationship between animals and human beings. Since the beginning of the modern animal rights movement, which was initiated by philosophers in the 1970s, animal rights has been a popular topic of discussion within the academic study of applied ethics, or the application of normative ethical theories to practical problems.

Philosophical background

The proper treatment of animals is a very old question in the West. Ancient Greek and Roman philosophers debated the place of animals in human morality. The Pythagoreans (6th–4th century bce) and the Neoplatonists (3rd–6th century ce) urged respect for animals’ interests, primarily because they believed in the transmigration of souls between human and animal bodies. In his biological writings, Aristotle (384–322 bce) repeatedly suggested that animals lived for their own sake, but his claim in the Politics that nature made all animals for the sake of humans was unfortunately destined to become his most influential statement on the subject.

Aristotle, and later the Stoics, believed the world was populated by an infinity of beings arranged hierarchically according to their complexity and perfection, from the barely living to the merely sentient, the rational, and the wholly spiritual. In this Great Chain of Being, as it came to be known, all forms of life were represented as existing for the sake of those forms higher in the chain. Among corporeal beings, humans, by dint of their rationality, occupied the highest position. The Great Chain of Being became one of the most persistent and powerful, if utterly erroneous, ways of conceiving the universe, dominating scientific, philosophical, and religious thinking until the middle of the 19th century.

The Stoics, insisting on the irrationality of all nonhuman animals, regarded them as slaves and accordingly treated them as contemptible and beneath notice. Aggressively advocated by St. Augustine (354–430), these Stoic ideas became embedded in Christian theology. They were absorbed wholesale into Roman law—as reflected in the treatises and codifications of Gaius (fl. 130–180) and Justinian (483–565)—taken up by the legal glossators of Europe in the 11th century, and eventually pressed into English (and, much later, American) common law. Meanwhile, arguments that urged respect for the interests of animals nearly disappeared, and animal welfare remained a relative backwater of philosophical inquiry and legal regulation until the final decades of the 20th century.

Animals and the law

In the 3rd or 4th century ce, the Roman jurist Hermogenianus wrote, “Hominum causa omne jus constitum” (“All law was established for men’s sake”). Repeating the phrase, P.A. Fitzgerald’s 1966 treatise Salmond on Jurisprudence declared, “The law is made for men and allows no fellowship or bonds of obligation between them and the lower animals.” The most important consequence of this view is that animals have long been categorized as “legal things,” not as “legal persons.” Whereas legal persons have rights of their own, legal things do not. They exist in the law solely as the objects of the rights of legal persons—e.g., as things over which legal persons may exercise property rights. This status, however, often affords animals the indirect protection of laws intended to preserve social morality or the rights of animal owners, such as criminal anticruelty statutes or civil statutes that permit owners to obtain compensation for damages inflicted on their animals. Indeed, this sort of law presently defines the field of “animal law,” which is much broader than animal rights because it encompasses all law that addresses the interests of nonhuman animals—or, more commonly, the interests of the people who own them.

A legal thing can become a legal person; this happened whenever human slaves were freed. The former legal thing then possesses his own legal rights and remedies. Parallels have frequently been drawn between the legal status of animals and that of human slaves. “The truly striking fact about slavery,” the American historian David Brion Davis has written, is the

antiquity and almost universal acceptance of the concept of the slave as a human being who is legally owned, used, sold, or otherwise disposed of as if he or she were a domestic animal. This parallel persisted in the similarity of naming slaves, branding them, and even pricing them according to their equivalent in cows, camels, pigs, and chickens.

The American jurist Roscoe Pound wrote that in ancient Rome a slave “was a thing, and as such, like animals could be the object of rights of property,” and the British historian of Roman law Barry Nicholas has pointed out that in Rome “the slave was a thing…he himself had no rights: he was merely an object of rights, like an animal.”

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In the late 18th and early 19th centuries, humanitarian reformers in Britain and the United States campaigned on behalf of the weak and defenseless, protesting against child labour, debtor’s prisons, abusive punishment in public schools, and, inevitably, the cruel treatment of animals. In 1800 the most renowned abolitionist of the period, William Wilberforce, supported a bill to abolish bull- and bearbaiting, which was defeated in the House of Commons. In 1809 Baron Erskine, former lord chancellor of England, who had long been troubled by cruelty to animals, introduced a bill to prohibit cruelty to all domestic animals. Erskine declared that the bill was intended to “consecrate, perhaps, in all nations, and in all ages, that just and eternal principle which binds the whole living world in one harmonious chain, under the dominion of enlightened man, the lord and governor of all.” Although the bill passed the House of Lords, it failed in the House of Commons. Then, in 1821, a bill “to prevent cruel and improper treatment of Cattle” was introduced in the House of Commons, sponsored by Wilberforce and Thomas Fowell Buxton and championed by Irish member of Parliament Richard Martin. The version enacted in 1822, known as Martin’s Act, made it a crime to treat a handful of domesticated animals—cattle, oxen, horses, and sheep—cruelly or to inflict unnecessary suffering upon them. However, it did not protect the general welfare of even these animals, much less give them legal rights, and the worst punishment available for any breach was a modest fine. Similar statutes were enacted in all the states of the United States, where there now exists a patchwork of anticruelty and animal-welfare laws. Most states today make at least some abuses of animals a felony. Laws such as the federal Animal Welfare Act (1966), for example, regulate what humans may do to animals in agriculture, biomedical research, entertainment, and other areas. But neither Martin’s Act nor many subsequent animal-protection statutes altered the traditional legal status of animals as legal things.

This situation changed in 2008, when the Spanish national parliament adopted resolutions urging the government to grant orangutans, chimpanzees, and gorillas some statutory rights previously afforded only to humans. The resolutions also called for banning the use of apes in performances, harmful research, and trading as well as in other practices that involve profiting from the animals. Although zoos would still be allowed to hold apes, they would be required to provide them with “optimal” living conditions.