The following is from The Dragons of Eden by Carl Sagan....
If chimpanzees have consciousness, if they are capable of abstractions, do they not have what until now has been described as "human rights"? How smart does a chimpanzee have to be before killing him constitutes murder? What further properties must he show before religious missionaries must consider him worthy of attempts at conversion?
I recently was escorted through a large primate research laboratory by its director. We approached a long corridor lined, to the vanishing point as in a perspective drawing, with caged chimpanzees. They were one, two or three to a cage, and I am 80 percent sure the accommodations were exemplary as far as such institutions (or for that matter traditional zoos) go. As we approached the nearest cage, its two inmates bared their teeth and with incredible accuracy let fly great sweeping arcs of spittle, fairly drenching the lightweight suit of the facility's director. They then uttered a staccato of short shrieks, which echoed down the corridor to be repeated and amplified by other caged chimps, who had certainly not seen us, until the corridor fairly shook with the screeching and banging and rattling of bars. The director informed me that not only spit is apt to fly in such a situation; and at his urging we retreated. I was powerfully reminded of those American motion pictures of the 1930s and 40s, set in some vast and dehumanized state or federal penitentiary, in which the prisoners banged their eating utensils against the bars at the appearance of the tyrannical warden. These chimps are healthy and well-fed. If they are "only" animals, if they are beasts which abstract not, then my comparison is a piece of sentimental foolishness. But chimpanzees can abstract. Like other mammals, they are capable of strong emotions. They have certainly committed no crimes. I do not claim to have the answer, but I think it is certainly worthwhile to raise the question: Why, exactly, all over the civilized world, in virtually every major city, are apes in prison?
For all we know, occasional viable crosses between humans and chimpanzees are possible.* The natural experiment must have been tried very infrequently, at least recently. If such off-spring are ever produced, what will their legal status be? The cognitive abilities of chimpanzees force us, I think, to raise searching questions about the boundaries of the community of beings to which special ethical considerations are due, and can, I hope, help to extend our ethical perspectives downward through the taxa on Earth and upwards to extraterrestrial organisms, if they exist.