Motherboard

Welcome to Evolution Explains, Motherboard’s weekly investigation into the human-animal (humanimal?) condition through the powerful scientific lenses of ecology and evolution. Don’t say you didn’t learn something. Now get to readin’ already.

Did you remember ever seeing a dog eat turds when you were a kid? Damn, that was hilarious. It’s one of the greatest mysteries messing with the minds of child biologists everywhere. But for the most part, people write it off like so: “Scruffy’s eating poop! Ha ha, dumb dog.” But are dogs really dumb for eating poop? I suppose the ‘dumb’ factor is debatable, but dogs aren’t alone in the poo-gobbling sector of the animal universe.

Hell, even humans eat shit. Actual human coprophagia is rare-to-nonexistent, but we do cram what amounts to shit into our bodies all the time. I suppose for legal reasons I must refrain to referring to specific fast food products as literal fecal matter, but you’ve all seen it happen: a woman stuffing processed animal byproducts covered in a secret sauce/chemical cocktail into her face or a guy who’s shoved so many cheese doodles into his body that his nutrient-absorbing intestinal villi are clogged with a neon-orange powder.

The question then is: why eat shit? I mean, we can’t all be eating organic quinoa salads and Purina One (that’s the fancy stuff) all the time. But it does seem weird to have abject cravings for such terrible food all the time. As always, evolution plays a role.

Thanks to the laws of thermodynamics and bioenergetics, no biological system can ever be 100 percent efficient, including digestive tracts. That means that, of all the nutrients that go into something’s mouth, some of those nutrients will come out its rear. In nature, those nutrients amount to a lot. In a classic example, hippopotamuses have long been studied for the amount of phosphorus and potassium they pump into African river systems. Turns out hippo herds pump out tons of high-grade fertilizer every year that help keep their rivers alive.

African rivers would die without hippo poo. These puppies are giant phosphorous machines.

So even gross shit has nutritional value. But why do organisms develop a taste for that and not something a lot better? From an evolutionary standpoint, it’s largely a product of the fact that our taste buds have evolved a lot more slowly than our current feelings about food. The Neolithic agricultural revolution (PDF), during which humans began to switch from being hunter-gatherers to farmers and herders, only occurred around 12,000 ago. Our modern diet has only really been around for at most a couple hundred years, and has fundamentally changed in even the last century, thanks largely to the increase in use of refrigeration systems.

Humans and dogs now have access to a nigh-unlimited stream of food but our physical centers for taste (tongue, brain, etc.) haven’t had much time to evolve beyond our former food-stressed lives. When we were stuck searching for food all day, our omnivore selves ate a lot of leaves and berries because they’re easier to catch than a juicy, meaty creature. Cravings can be a weirdly logical thing, as evidenced by some of the absurd things eaten by pregnant women. It’s like your body says: “The baby needs something found in sauerkraut and Sriracha. EAT A PINT OF BOTH.”

At their core, cravings have been shaped to fit our past food cirumstances. Salt and calorie-dense fat were hard to find but incredibly valuable. When we found some, we pigged out, like we see now in nature when predators stuff themselves silly. It’s a basic concept: if something’s rare and essential, we’ll take it however we can get it, and our tastes will evolve to entice us to do so.

Historians say salt used to be worth its weight in gold. We need salt to live. You want this.

The dog eating his turds most likely doesn’t see it as gross, at least not in our sense of the word. Rather, that poo nugget is a nutrient-dense plate of leftovers. In the wild, that’d be tough to pass up. Of course, this isn’t an across-the-board rule but rather a concept whose degree of application varies across the diverse animal spectrum. For example, you’d never find a zebra eating lion dookie, while entire populations spring up on the ocean floor to feast on fish waste and whale carcasses.

The point is that tastes evolved to demands that some of us animals just don’t have to deal with. It’s the same reflex that causes some dogs to eat everything that’s put in front of them, and even in humans there’s a certain amount of pleasure in stuffing your face. We aren’t beholden to our innate tastes, as evidenced by the multitudes of vegans and dogs who eat nothing but Cesar canned food. There’s also a huge behavioral component that we’ll have to discuss at another time. In essence: if you see your mom eating shit, you’ll probably figure shit’s pretty good for you too.

At the same time, it’s pretty hard to turn down a big hunk of salty, fatty food, especially when it’s processed to fit your exact evolved cravings. In the same way, your dog may just see a steaming pile of dookie in the same way we look at a cheeseburger: a whole bunch of cheap nutrients that our bodies need. These days, we’ve got plenty of other, healthier outlets to find those things, which makes it easier to both avoid and despise them. Despite that, the desire is still there.

Thus, is evolution’s effect on taste the cause, or worse, an excuse, for people eating unhealthily? Hell no. Both canines and us have more access to great food than any other point in history, and there’s no reason to go shoving shit in your mouth. Dogs and people prove every day that we’re more than capable of modifying our behavior to fit our current situations. We’re never fully chained to the bonds of evolution, at least not in a behavioral sense. That doesn’t change the fact that millions of years of living in the wild have shaped our tastes.

The next time you find yourself drooling over some shit, don’t blame yourself. It’s how you’ve evolved.

PREVIOUSLY EVOLUTION EXPLAINED…
The Evolutionary Perfection of Juggalos and Birds-of-Paradise

Photos via 1, 2, 3