No Other Animals Do That

In this article I want to examine a really bad kind of argument. You’ve probably heard it before. For some reason, this style of argument is especially popular when it comes to drinking milk. People will say things like, “You don’t see gorillas drinking cow’s milk” or “Did you know that humans are the only animals on earth that drink milk beyond infancy?” The implication is that these (supposed) facts about the behavior of other animals give us some reason to think that we humans shouldn’t drink milk. For now, I’m not actually concerned with whether the biological claims are true. What I’m concerned with is why someone would think—supposing the biological claims were true—they would have implications for how humans ought to live.

Though this style of argument is most popular when it comes to milk, it can be applied to other kinds of behaviors. The general form of the argument is:

1. No species on Earth, besides humans, engages in behavior type B.
2. If no other species engage in B, then humans shouldn’t engage in B.
3. Therefore, humans should not engage in B.

I’m puzzled by the popularity of this form of argument. It is valid. That is, the conclusion follows if the premises are true. However, it strikes me as an obviously unsound argument. That is, one or more of the premises is not true. I’m granting premise (1), though in many cases it too is likely false. I’m willing to ignore that premise, because the more general problem is that (2) is almost certainly false.

One sees this exact same style of argument from certain religious conservatives who say things like, “You don’t see homosexuality in nature.” Again, for now I’m not actually concerned with whether there is any truth to this biological claim. (I’m pretty skeptical, for the record.) What’s puzzling to me is that anyone would think — supposing it were true — that a biological fact like this has the slightest bit of relevance to what human beings ought to do. What other animals do seems irrelevant to questions like: “What would be good for me to do?” and “How should I live?” In philosophical jargon, facts about the behavior of other species are “normatively irrelevant” when it comes to our own lives. Considerations like that just don’t have any bearing on what one ought to do.

The other problem, as suggested by the last example, is that arguments like this prove too much. The majority of human activities are things that no other animals do. No other species on Earth makes and wears clothes, or drives cars, or builds skyscrapers, or uses spoken or written language, or does science or philosophy, or… So, if the argument schema above were any good, it would indict almost everything that we do — and certainly the most interesting things that we do.

Indeed, there is a long tradition of thought, going back at least to Aristotle, according to which the humanly unique traits and behaviors are good things. For Aristotle, the capacity to reason is the key distinguishing feature of humankind. Our rationality, he thought, is what’s so special and great about our species. This line of thought was continued by Medieval Christian thinkers, who thought that what distinguishes humans from mere beasts is that we have a soul. Regardless of what one thinks of such claims, humans are very different from other animals. And it’s quite implausible that the things we do differently are necessarily, or even probably, defects or mistakes.

So, if “no other animals do that” arguments are so bad, then why do people like them? In my more charitable moods, I’m inclined to think that there must be a decent argument in the neighborhood of this one, which somehow lends credibility to this bad neighbor. I’ll suggest one contender below. But I don’t think I’ve found a sound counterpart. Perhaps readers can help me out with that.

As I said above, what other species do seems to be normatively irrelevant. Biological facts about the behavior of other species have no weight in human practical deliberation. But, perhaps what other species do has some epistemic weight. That is to say, maybe we should consider the (putative) fact that no other animals engage in B to be a reason to reevaluate why we think it’s good or acceptable to engage in B. So the new argument would be:

1. No species on Earth, besides humans, engages in behavior type B.
2. If no other species engage in B, then humans should carefully evaluate the merits of engaging in B.
3. Therefore, humans should carefully evaluate the merits of engaging in B.

The idea here is that premise (1) should lead us to ask whether there is a good reason why other animals don’t engage in B. So, we should look for that reason and see if it applies to humans as well. This thought might be motivated by a sense that, if animals don’t do B, then B must be evolutionarily maladaptive, or some such thing. This sounds reasonable. But, it’s also trivial. We should evaluate the merits of all of our activities. To do otherwise would be to live mindlessly and unreflectively. (I feel compelled to cite Socrates’ most famous line: “the unexamined life is not worth living”.) So, we ought to carefully consider the merits of B, regardless of how many other animals engage in B.

As much as I prefer to interpret people charitably, I frankly don’t see how to produce a good argument here. I take it that the underlying intuition is that, if other animals don’t engage in B, then B is unnatural. The problem is that this claim is incredibly vague. It’s not at all clear what it means for something to be unnatural, or why unnaturalness is a bad thing. Unless we’re able to spell out this notion in a way that shows why it’s normatively relevant, I just don’t see how “other animals don’t do that” arguments are ever going to get off the ground.