Lawyer and animal rights activist Steven Wise's book, Drawing the Line, does three things: (1) It explains what makes a person a person; (2) It provides a person-continuum of 0.0 (mere stimulus-response machines) to 1.0 (full autonomy–which is what Wise identifies as the essence of personhood); (3) It tells us that any animal with a score above .70 should be considered a person with legal rights. Elephants score the highest on Wise's continuum and are therefore entitled to legal rights, like people. Other animal-people are parrots, dolphins, gorillas, and bonobos, all of which score higher than .70. Further testing might show that other animals surpass the .70 mark.
It all doesn't really matter to me. Just as long as I can still eat 'em.