The animal kingdom contains a wide range of animals that could be considered “persons”, which we are learning as scientists stop imposing human assumptions and instead learn how they interact in their own environment. As a consequence, we are realizing that we have grossly underestimated both the scope and the scale of animal intelligence. Evolution would be inexplicably discontinuous if only humans, or only mammals, or only vertebrates were self-aware. One of the measures of intelligence used is the mirror test for self-recognition, and elephants, chimpanzees, dolphins, and magpies all passed with flying colors.
More important, though, than simple self-recognition is what is referred to as being the subject-of-a-life. Does the entity have a sense of continuity over time, of engagement in a life process? If the answer is “yes,” then harm would limit or cut short those future possibilities. A corollary of that sense of having one’s own perspective is metacognition (thinking about thinking), which research has demonstrated occurs in at least cetaceans and chimpanzees.
Much of the focus of research has been in the arena of intelligence, decision-making, and problem solving, and there is now ample evidence that elephants and cetaceans (whales and dolphins) in particular are very intelligent, second only to humans. Indeed, research is demonstrating that a growing range of vertebrates could be considered nonhuman persons:
- Cetaceans: Whales and dolphins
- Great apes and other primates
- Other vertebrate species
 C. Siebert, “Animals Like Us,” Popular Science (January 2015): 52-55.
 J. Dunayer, “The Rights of Sentient Beings: Moving Beyond Old and New Speciesism,” in The Politics of Species: Reshaping Our Relationships with Other Animals, ed. R. Corbey & A. Lanjouw, 27-39 (Cambridge: Cambridge University Press, 2013).
 D. Reiss & L. Marino, “Mirror Self-Recognition in the Bottlenose Dolphin: A Case of Cognitive Convergence,” PNAS 98 (2001): 5937-5942.
 T. Regan, The Case for Animal Rights (Berkeley: University of California Press, 1983).
 L. Marino, R.C. Connor, R.E. Fordyce, L.M. Herman, P.R. Hof, L. Lefebvre, D. Lusseau, B. McCowan, E.A. Nimchinsky, A.A. Pack, L. Rendell, J.S. Reidenberg, D. Reiss, M.D. Uhen, E. Van der Gucht, & H. Whitehead, “Cetaceans Have Complex Brains for Complex Cognition,” PLoS: Biology 5, no. 5 (2007).
 M.J. Beran, J.D. Smith, & B.M. Perdu, “Language-Trained Chimpanzees (Pan Troglodytes) Name What They Have Seen But Look First at What They Have Not Seen,” Psychological Science 24, no. 5 (2013): 660-666.