On the ethical basis of Animal Rights

Peter Singer: Equal consideration of interests
Peter Singer is a utilitarian, not a rights theorist.

Singer is an act utilitarian, or more specifically a preference utilitarian, meaning that he judges the rightness of an act by its consequences, and specifically by the extent to which it satisfies the preferences of those affected, maximizing pleasure and minimizing pain. (There are other forms of utilitarianism, such as rule utilitarianism, which judges the rightness of an act according to the usual consequences of whichever moral rule the act is an instance of.)

Singer's position is that there are no moral grounds for failing to give equal consideration to the interests of human and non-humans. His principle of equality does not require equal or identical treatment, but equal consideration of interests. A mouse and a man both have an interest in not being kicked down the street, because both would suffer if so kicked, and there are no moral or logical grounds, Singer argues, for failing to accord their interests in not being kicked equal weight.[93] Singer quotes the English philosopher Henry Sidgwick: "The good of any one individual is of no more importance, from the point of view ... of the Universe, than the good of any other."[77] This reflects Jeremy Bentham's position: "[E]ach to count for one, and none for more than one." Unlike the position of a man or a mouse, a stone would not suffer if kicked down the street, and therefore has no interest in avoiding it. Interests, Singer argues, are predicated on the ability to suffer, and nothing more, and once it is established that a being has interests, those interests must be given equal consideration. The issue of the extent to which animals can suffer is therefore key.
[edit] Animal suffering

Singer writes that commentators on all sides of the debate now accept that animals suffer and feel pain, although it was not always so. Bernard Rollin, a philosopher and professor of animal sciences, writes that Descartes' influence continued to be felt until the 1980s. Veterinarians trained in the U.S. before 1989 were taught to ignore pain, he writes, and at least one major veterinary hospital in the 1960s did not stock narcotic analgesics for animal pain control. In his interactions with scientists, he was often asked to "prove" that animals are conscious, and to provide "scientifically acceptable" evidence that they could feel pain.[94]

Singer writes that scientific publications have made it clear over the last two decades that the majority of researchers do believe animals suffer and feel pain, though it continues to be argued that their suffering may be reduced by an inability to experience the same dread of anticipation as humans, or to remember the suffering as vividly.[95] In the most recent edition of Animal Liberation, Singer cites research indicating that animal impulses, emotions, and feelings are located in the diencephalon, pointing out that this region is well developed in mammals and birds.[96] Singer also relies on the work of Richard Sarjeant to support his position. Sarjeant pointed out that non-human animals possess anatomical complexity of the cerebral cortex and neuroanatomy that is nearly identical to that of the human nervous system, arguing that, "[e]very particle of factual evidence supports the contention that the higher mammalian vertebrates experience pain sensations at least as acute as our own. To say that they feel less because they are lower animals is an absurdity; it can easily be shown that many of their senses are far more acute than ours."[97]

The problem of animal suffering, and animal consciousness in general, arises primarily because animals have no language, leading scientists to argue that it is impossible to know when an animal is suffering. This situation may change as increasing numbers of chimps are taught sign language, although skeptics question whether their use of it portrays real understanding. Singer writes that, following the argument that language is needed to communicate pain, it would often be impossible to know when humans are in pain. All we can do is observe pain behavior, he writes, and make a calculated guess based on it. As Ludwig Wittgenstein argued, if someone is screaming, clutching a part of their body, moaning quietly, or apparently unable to function, especially when followed by an event that we believe would cause pain in ourselves, that is in large measure what it means to be in pain.[98] Singer argues that there is no reason to suppose animal pain behavior would have a different meaning.