From the Chronicle of Higher Education:
In 55 BC, the Roman leader Pompey staged a combat between humans and elephants. Surrounded in the arena, the animals perceived that they had no hope of escape. According to Pliny, they then “entreated the crowd, trying to win its compassion with indescribable gestures, bewailing their plight with a sort of lamentation.” The audience, moved to pity and anger by their plight, rose to curse Pompey — feeling, wrote Cicero, that the elephants had a relation of commonality (societas) with the human race.
In 2000 AD, the High Court of Kerala, in India, addressed the plight of circus animals “housed in cramped cages, subjected to fear, hunger, pain, not to mention the undignified way of life they have to live.” It found those animals “beings entitled to dignified existence” within the meaning of Article 21 of the Indian Constitution, which protects the right to life with dignity. “If humans are entitled to fundamental rights, why not animals?” the court asked.
We humans share a world and its scarce resources with other intelligent creatures. As the court said, those creatures are capable of dignified existence. It is difficult to know precisely what that means, but it is rather clear what it does not mean: the conditions of the circus animals beaten and housed in filthy cramped cages, the even more horrific conditions endured by chickens, calves, and pigs raised for food in factory farming, and many other comparable conditions of deprivation, suffering, and indignity. The fact that humans act in ways that deny other animals a dignified existence appears to be an issue of justice, and an urgent one.
More here.