About five years ago, I stopped eating anything smarter than my cat. This, I decided, spared all non-rodent mammals, as well as cephalopods—the latter thanks to an 11th-hour magazine piece on octopus ingenuity. Everything else was on the menu.

Friends have quibbled with my sorting. There’s no way a cow is smarter than a cat. Even your cat. I have no grand defense. Mine is a stance honed not by reason but by gut feel—more Citizen Kane vs. The Godfather than Pythagorean theorem. How the hell do I know whether my cat is smarter than a cow? How could anyone?

The problem is that though some animals laze in Chicago apartments, others dwell in rural pastures or factory farms or rainforest canopies or 1,000 feet underwater. Some animals live in small groups, others in solitude, and still others in flocks thousands strong. Just last week I learned that a limiting factor for tool use—the smoking gun of animal intelligence—may well be physical dexterity: the dumb, lucky ability to clamp or poke or push things around with some precision. Ranking the intelligence of animals born into such different environments, family units, and bodies is as futile as it is irresistible.

Nor is it unproblematic that we humans have a complete monopoly on IQ test design and implementation. As the Emory University primatologist Frans de Waal recently described, this has led to a number of anthropocentric mishaps: testing whether elephant-sized elephants could identify their own reflections inside human-sized mirrors, or investigating facial recognition in primates using human faces rather than primate ones. Whoops.

But really, we needn’t look much beyond our own species to determine the absurdity of pitting fruit bats against iguanas. Ravens Progressive Matrices is an IQ test designed to be culturally neutral: participants complete geometric puzzles—no culturally encrusted words required. But the very quality that makes the test culturally universal also limits its interpretability, Sarah Judkins, a clinical psychologist at Gonzaga University, tells me: Just which aspects of intelligence are being tested with a completely nonverbal test? And what, moreover, is culturally neutral about sitting across the room from a psychologist, solving puzzle after puzzle?

Or forget cross-cultural comparisons. Consider comparing children to adults, or young adults to the elderly. Ohio State psychologist Roger Ratcliff has demonstrated again and again that different age groups’ performance on cognitive tasks—even simple things like deciding whether a visual array has few or many asterisks—cannot be easily compared. Over the course of our lives, we have different sensory capabilities, expectations, and strategies.

The truth is, whenever two populations approach a task differently, comparisons should be cautious. When these populations come from two drastically different species, caution may not be enough.

Does this mean we shouldn’t try? No. I see no reason why we shouldn’t embrace the opportunity to understand what animals are capable of—generosity in rats? Cultural transmission among damselfish?—and allow what we learn to shape our own behavior. But we should recognize that whatever ranking system we impose—to live with ourselves and with the havoc we are wreaking on the rest of the animal kingdom—is pure folly. And then we should probably go get something to eat.