Does "Appeal to Nature" Justify Eating Meat?

Perhaps you’ve heard the joke about a woman driving down the highway with moonshine equipment in the back of her flatbed?

A cop pulled her over and said he’d have to arrest her for making liquor.
"But I wasn't making liquor!" said the woman.
"You've got all the equipment for it!" the cop snapped back.
"Yeah, but that doesn't mean I'm making it."
"Well, I have to take you in."
“In that case,” said the woman, “I’ll have to charge you with sexual assault.”
“But I haven’t touched you,” exclaimed the officer.
The woman replied, “You’ve got all the equipment for it.”

Just because we've got the equipment for it doesn't mean we have, or ought, to do it.

We have the equipment for eating meat. We have incisors for biting into meat and a digestive tract that can process and use nutrients from the flesh of other animals.

We evolved to eat meat. But we didn't evolve for there to be seven billion of us. More precisely, evolution equipped us fairly well for survival in the world of a million years ago but not for living sustainably in a world headed toward nine billion humans by 2055 consuming resources at the rate we do. Indeed, because genetic evolution inherently rewards higher reproduction, it is unsuited for the adaptation now required. If we're all going to be fed, and fed sustainably, our social and moral evolution, rather than our genetic evolution, will have to do the adapting. We will have to decide to forgo the resource waste, greenhouse-gas emissions, and pollution of meat production.

The argument that "it's natural for us to eat meat" is a form of the "appeal to nature" fallacy, which takes the form “X is natural; therefore, X is good.” The premise invokes a term, "natural," that is highly ambiguous and equivocal: we don’t have any agreement on how to distinguish “natural” from “unnatural,” and even if we did, nature is in a constant process of producing aberrations, some of which eventually become norms. The natural/unnatural divide is constantly shifting. Moreover, the conclusion simply doesn’t follow: even if we unequivocally agreed that something was “natural” that would tell us nothing about acceptable or unacceptable behavior.

Yet “appeal to nature” arguments do keep popping up. Perhaps this is because -- psychologically, if not logically -- we are attracted to pattern our social and moral reasoning after patterns we (think we) see in nature. Norms play a role, if not a determinative role, in our moral reasoning, and nature, in one way or another, does generate a lot of norms. It will not suffice for vegetarians to simply wave the "fallacy" flag. If we can't help ourselves from looking to nature as a teacher, then let us look more carefully at what nature really teaches.

Appropriating a structure that served one purpose and putting it to a very different purpose is a common maneuver in evolution's playbook. Mammalian forelimbs get turned into bat wings – or dolphin fins. Antennae get turned into mandibles. A jaw bone in dinosaurs, fish, and reptiles got appropriated and made into an auditory bone in mammals. An ancestor of wasps and bees had an ovipositor that got appropriated and made into a stinger.

Before there were land animals, certain fish developed a swim bladder, which they could fill with gas, usually air. This allowed the fish to stay at a given depth without expending energy on swimming. The swim bladder probably was, in some species, also helpful for stability, and maybe also as a resonating chamber to produce or receive sound. The swim bladder evolved into the lung of the earliest lungfish – and from there into the lungs of land animals. Something that evolved for one purpose or set of purposes (buoyancy, stability, sonic resonance) was appropriated for a very different purpose (breathing air). A device for staying at a given depth in water turned into the essential step for moving onto land!

Structures that served one purpose get put to very different purposes. Happens all the time. The fact that we have a given structure does not obligate us to continue the purpose for which that structure evolved. Genetic evolution is under no such constraint; if it were, then swim bladders would never have turned into lungs, and we’d all still be fishes.

As genetic evolution appropriates structures and puts them to new purposes, so, too, can our social and moral evolution. We can choose to put our body's meat-processing apparatus to vegetarian purposes. This is every bit as “natural” as eating meat is. It's also, in fact, healthier.

“Nature” gave us a lot of “equipment.” It’s up to us how, and whether, to use it. It's "natural" for men to sexually assault women: rape occurs in every culture throughout history. That doesn't make it OK. Morality trumps male predisposition toward violently aggressive sexual expression. We would never stand for an appeal to nature argument attempting to justify rape.

Sexuality, of course, can also be used in loving, healing ways. Those ways are often nonreproductive, which further illustrates the point. While our reproductive organs evolved to serve the purpose of reproduction, we use them, with less and less guilt and shame these days, for intimacy and connection in ways that do not lead to reproduction. We appropriate what evolution provided and put it to purposes other than the function for which it evolved. Our reproductive system can reproduce -- but it's just fine if it doesn't. Our digestive system can handle meat -- but it's just fine if it doesn't.

With the fallacious “appeal to nature” out of the way, we are free to use our moral capacity to reflect on the level of suffering, and the level of environmental damage, our dietary choices may inflict.