Most of us believe that eating animals is natural because humans have consumed animals for millennia. And it is true that we have been eating animals as part of an omnivorous diet for at least two million years (though for the majority of this time our diet was still primarily vegan). But to be fair, we must acknowledge that infanticide, murder, rape, and cannibalism are at least as old as eating animals, and are therefore arguably as “natural”—and yet we don't invoke the longevity of these acts as a justification for them. As with other acts of violence, when it comes to eating animals, we must differentiate between natural and justifiable. At three or four stations along the treasure hunt clues are accompanied by sweets and treats.
The way “natural” translates to “justifiable” is through the process of naturalization. Naturalization is natural as normalization is too normal. When an ideology is naturalized, its tenets are believed to be in accordance with the laws of nature (and/or the law of God, depending on whether one's belief system is science- or faith-based, or both). Naturalization reflects a belief in the way things are meant to be; eating animals is seen as simply following the natural order of things. Naturalization maintains an ideology by providing it with a (bio)logical basis.
Like norms, many naturalized behaviors are constructed, and it should come as no surprise that they're constructed by those who place themselves at the top of the “natural hierarchy.” The belief in the biological superiority of certain groups has been used for centuries to justify violence: Africans were “naturally” suited to slavery; Jews were “naturally” evil and would destroy Germany if not eradicated; women were “naturally” designed to be the property of men; animals “naturally” exist to be eaten by humans. Consider, for instance, how we refer to the animals we eat as though nature designed them for this very purpose: we call them “farm” (rather than “farmed”) animals, “broiler chickens,” “dairy cows,” “layer hens,” and “veal calves.” Even the great logician Aristotle invoked biology and bent logic to suit the norms of his era, when he asserted that males were naturally superior to females and slaves were biologically designed to serve free men. And consider one of the central justifications for carnism, the natural order of the so-called food chain. Humans supposedly reside at the “top” of the food chain—yet a chain, by definition, doesn't have a top; and if it did, it would be inhabited by carnivores, not omnivores.
The key disciplines that support naturalization are history, religion, and science. History presents us with a selective historical focus and “facts” that prove the ideology has always existed. The historical lens internalizes the ideology, making it seem as if it always has been, and therefore always will be, the way things are. Religion upholds the ideology as divinely ordained, and science provides the ideology with a biological basis. The importance of religion and science in naturalizing an ideology helps to explain why spirituality and intelligence have been popular criteria by which a group defines itself as naturally superior.
For instance, before animal experimentation was a common scientific practice, the mathematician and philosopher René Descartes nailed the paws of his wife's dog to a board in order to dissect him alive and prove that, unlike humans but like other animals, the dog was a soulless “machine” whose cries of pain were no different from the springs and wheels of a clock automatically reacting when dismantled. And Charles Darwin argued that because males were supposedly born with a greater capacity for reason than females, over the course of evolution men have become superior to women. In short, naturalization makes the ideology historically, divinely, and biologically irrefutable.