There are barbarians who seize this dog, who so greatly surpasses man in fidelity and friendship, and nail him down to a table and dissect him alive, to show you the mesaraic veins! You discover in him all the same organs of feeling as in yourself. Answer me, mechanist, has Nature arranged all the springs of feeling in this animal to the end that he might not feel?
Voltaire (Dictionnaire philosophique portatif, 1764)
The mechanist Voltaire mentions is actually a reference to the idea that all things, including living things can be understood solely by understanding the laws of nature and some initial set of conditions. Life under this view is no more than a complex machine that could be broken down into component parts and better understood. This reductionism is very much essential to science, and everything we know does suggest that nature abides by its own laws. Rene Descartes was a proponent of mechanism in most cases, but struggled with the idea that the human mind and consciousness that he experienced could be explained simply by natural interactions. Descartes posited that in the case of humans we must posses some “mental substance” that was not material to explain all the sensations we feel in our lives, but that non-human animals did not have this additional mental component and thus could not feel pain. This argument was used to justify immensely cruel acts in the 17th and 18th centuries and it was in the context of these cruel acts that Voltaire raised his challenging question. Clearly there is no logical reason why we should find the mechanisms for feeling in non-human animals if they are not to feel; nonetheless, this Cartesian argument is still one we hear commonly raised today.
Another way to do it would be to hybridize humans and chimpanzees, produce an actual hybrid, and the point of the novel would be to explore the implications. What effect would that have on society? What effect would that have on moral philosophy? What effect would that have on religion?
Richard Dawkins (Point of Inquiry, Dec. 7 2007)
At present our legal system has not defined the place a human chimpanzee hybrid would inhabit. Should it be granted the same freedoms we enjoy ourselves? Should it be subjected to the same confinement and experimentation we would subject chimpanzees to? What about a 3/4 or a 1/4 human version? Perhaps this blurring of our own species line might finally make clear that species should not be the morally relevant characteristic that determines whether a being deserves consideration for its interests.
But if the experimenter claims that the experiment is important enough to justify inflicting suffering on animals, why is it not important enough to justify inflicting suffering on humans at the same mental level?
Peter Singer (Animal Liberation, 2002, p.83)
People who try to justify rights for only humans often do so on the basis that humans have some exceptional mental characteristic. There are certainly a number of things we see humans doing that we do not see amongst other animals, but these things aren't things done by all humans. When we use these rules to justify differential treatment for human and non-human animals we need to acknowledge that humans who do not meet the requirements for these rules do not receive the protections from these rules.
The day has been, I grieve to say in many places it is not yet past, in which the greater part of the species, under the denomination of slaves, have been treated by the law exactly upon the same footing, as, in England for example, the inferior races of animals are still. The day may come when the rest of the animal creation may acquire those rights which never could have been witholden from them but by the hand of tyranny. The French have already discovered that the blackness of the skin is no reason a human being should be abandoned without redress to the caprice of a tormentor. It may one day come to be recognized that the number of the legs, the villosity of the skin, or the termination of the os sacrum are reasons equally insufficient for abandoning a sensitive being to the same fate. What else is it that should trace the insuperable line? Is it the faculty of reason or perhaps the faculty of discourse? But a full-grown horse or dog, is beyond comparison a more rational, as well as a more conversable animal, than an infant of a day or a week or even a month, old. But suppose the case were otherwise, what would it avail?
Jeremy Bentham (Introduction to the Principles of Morals and Legislation, 1789)
Perhaps you don't speak quite the same way as Bentham did in 1789, but those who treat human and non-human animals by different sets of standards ought to be able to answer what it is that traces the insuperable line. Bentham also makes the excellent point that even if humans are more reasonable than non-human animals this doesn't mean non-human animals should be subjected without redress to the caprice of a tormentor. Bentham answers the question of the insuperable line for himself suggesting that the ability to suffer is what traces the line.
But if we should ask these profound expositors of God’s intentions, How about those man-eating animals - lions, tigers, alligators - which smack their lips over raw man? Or about those myriads of noxious insects that destroy labor and drink his blood? Doubtless man was intended for food and drink for all these? […] Now, it never seems to occur to these far- seeing teachers that Nature’s object in making animals and plants might possibly be first of all the happiness of each one of them, not the creation of all for the happiness of one. Why should man value himself as more than a small part of the one great unit of creation?
John Muir (A Thousand-Mile Walk to the Gulf, 1916)
I often hear from omnivores that animals eat each other, therefore that somehow justifies us eating them, strangely with no bother to explain how herbivorous cattle made their way onto our menus. Nevertheless, whenever any animal tries to return the favor upon a member of human-kind the act is universally condemned. How is it people determined that non-human animals were placed here for our consumption, but certainly not us for theirs? We are a much smaller part of this cosmos than could have ever been realized in Muir's time. We should be grateful to enjoy a part in it, but we certainly do not properly appreciate its beauty if we believe the cosmos, in all of its entirety, was created solely for our own purposes.
If a group of beings from another planet were to land on Earth - beings who considered themselves as superior to you as you feel yourself to be to other animals - would you concede them the rights over you that you assume over other animals?
(Possibly)George Bernard Shaw
This quote has been repeated in a number of different forms by a number of different people. I most commonly see it attributed to George Bernard Shaw; although, I was unable to track down the original source in which it appeared, so take that attribution with a grain of salt. The point of this comment, however, is fairly clear. There may very well exist beings in this universe whose intellect and technological prowess far exceeds our own. To them, we may not appear particularly exceptional amongst the numerous beings that inhabit this planet (or region of the universe). Most of us agree that it wouldn't be right for them to treat us as we currently treat non-human animals, but why not?
Consider those unfortunate mentally impaired people who have much less capacity to solve problems, to care for themselves, to communicate, to engage in social relationships and to feel pain, than do apes. What is the logic that forbids medical experiments on those people, but not on apes?
Jared Diamond (The Rise and Fall of the Third Chimpanzee, 1991)
Perhaps these severely mentally impaired humans have less impaired humans who deeply care about them and would be hurt by their loss, but it is not out of the question to find severely mentally impaired orphans whose disappearance would not particularly concern anyone. I suspect many of us would still find it wrong to subject them to excruciating experiments or to keep them confined and lonely without social interaction. Yet many great apes capable of enjoying life at a seemingly much higher level are subjected to these sorts of conditions regularly. Why do we allow this to happen, but forbid the experiments on much less deserving humans?
When nonvegetarians say that “human problems come first” I cannot help wondering what exactly it is they are doing for human beings that compels them to continue to support the wasteful, ruthless exploitation of farm animals.
Peter Singer (Animal Liberation, 2002, p.221)
I understand that this is not an actual question, but I have chosen to include it since it can easily be reworded as such. I can easily see people believing that they are personally more equipped to deal with issues pertaining to humans than non-humans, but even so, there is no reason to continue to support the exploitation of non-human animals just because you have put human issues as your primary concern.
Why should species, genus, and family be relevant to the assignment of legal rights?
Steven M. Wise (Drawing the Line: Science and the Case for Animal Rights, p.24)
Steven Wise is an excellent animal rights author, and makes an important point early on in his book. Linnaean categorizations should not be what determines whether a being is deserving of rights. Only the characteristics of each individual should be relevant to determining the consideration each receives.