To avoid the question of granting rights to nonhuman animals on Earth, the word sentient is used interchangeably with intelligent, which is regarded as a characteristic unique to humans. In this respect, popular science fiction returns to the 18th-century view of rights, which Bentham criticized. But while intelligence is not a reasonable requirement for determining who is entitled to legal protection, the clearest case for animal rights can be made by starting with animals, such as apes and whales, who are clearly intelligent. PETA's ignorance of wildlife protection issues points out the problem with the simplistic idea that all members of the animal kingdom, from insects to primates, are morally equivalent. While animal rights activists use the term animal in its biological sense of the animal kingdom, rather limiting it to the legal sense of mammals, there is no ethical or scientific reason why rights should be granted to all members of a biological kingdom.
Biologists identify a major subdivision of a kingdom as a phylum.
The phylum Chordata encompasses all organisms with a central nervous system, i.e. a brain and spinal cord. It is not only modern scientific taxonomy which defines vertebrates as a major subdivision of the animal kingdom. Gandhi based his movement of nonviolent civil disobedience on the principle of ahimsa. Pranatipata viramana is also the first precept of Buddhism. Buddhism begins with the fundamental truth that all sentient beings experience suffering.