This isn’t pretty. But it is fact. The annals of exploration are full of gruesome tales of cannibalism.

In naval circles it was well known that if a ship ran aground on a deserted island, the custom of drawing lots and killing and eating each other one by one was the norm. A 1536 English expedition landed on the Labrador coast with their main ship badly foundering. Unable to hunt, gather enough nutrition, or navigate home, they killed and ate each other. A few centuries later, and probably most famously, the ship The Essex was sunk by a giant whale that rammed it. The survivors resorted to eating each other. The whale-ramming part of this story you know, from Moby-Dick, though Melville’s 1851 novel focuses on the man vs. whale yarn and entirely skips the ignoble man-eating-man bits.

But you can’t keep such horrors buried forever, and at exactly the same time Sir John Franklin’s search for the Northwest Passage ended in an ice-bound disaster on an island in the Polar Sea. Nobody knows for certain how Franklin’s expedition fell apart, but an 1854 rescue party came back from the wreckage reporting evidence of cannibalism. It sent shockwaves through proper British society, with Charles Dickens trying desperately to save face by propagating an alternate theory that the Inuit had attacked and eaten the men instead of them eating each other.

You get the point. We need to eat to survive. And time and again, we’ve eaten each other to do so.

Which is why we’re taking a look at the worst-case scenario coldly and rationally. If you had no other choice, how should you go about it? What should you eat first? What shouldn’t you eat, and why?

One presumption: This should be obvious, but the most important thing is that you’re starving. We’re not going to suggest you go Hannibal Lector. The idea is that if you were on a polar, desert, mountain, sea or otherwise journey and all the hunting and gathering you could muster wasn’t sufficiently staving off starvation, and one or more of your posse dies (maybe you get “lucky” and he runs off a cliff chasing after a very tasty looking rabbit), shouldn’t you then consider that now-dead person as food? Yes, it goes against all cultural norms, but setting emotions and morality aside, the human body is comprised of minerals, vitamins, fat, carbohydrates, and protein, and that makes them potential food.

So now what? Let’s start with the what-to-eat business.

You know how in zombie movies they’re always opining about the yumminess of human brains? Turns out, zombies are smarter than you think. That is, you want to eat the brains first, according to Dr. Jeffrey Schwartz, an evolutionary biologist at the University of Pittsburgh who knows his brains from his heart — and he knows the history of cannibalism as well, both ancient and recent.

Schwartz says that among tribes that preyed on people and then ate them, tribal leaders were always given the brains and livers. You might think you’d eat your enemy’s heart, but that’s a Hollywood invention — and while cannibalism may have been largely symbolic, food is still food. “The brain is all fat,” Schwartz explains, noting that whether you’re a member of an ancient society always fearing starvation or a modern human about to starve to death, fat is a must for survival.

He cautions that by eating brains you’re risking BSE (“mad cow” disease) but the math here is on surviving until tomorrow, not into old age, and you need fat immediately to convert to carbohydrates and sugars. And you’d get fat from the liver, as well as vitamin A, which you’re bound to be deficient in if you’re starving to death. Vitamin A is critical for vision, bone strength, nerve function, disease resistance, and (ironic when you’re starving) digestion of other nutrients. You can O.D. on liver, leading to a Vitamin A overdose that causes all sorts of other issues, but we’re hoping that you don’t have to rely on eating people brains and people livers like a gorging zombie, okay? Good.

Next, you’d go for other internal organs, because they’d be the best sources of any residual fats in a starving person, as well as minerals, and along with sheer calories you’re looking for nutrients that will restore you. Schwartz cautions that you want to avoid the intestines and the colon because they’re full of toxins, but the rest of the innards are prime sources of energy.

Why not the torso? The gut at least is likely to retain a little fat, right?

Schwartz explains that it takes a lot of energy to break down protein, and we’re presuming that everyone’s been deprived of Tostitos and guac for quite some time, so the calories to break down muscle have to first be obtained by eating up the fat stored in your dead former friend. Yes, the “domesticated” human has advantages over eating the lean muscle of a deer; for one thing, there’s no fur, and skinning a human, disgusting as it would be, wouldn’t be as much work or take as much energy, which is good because remember you haven’t got a calorie to spare.

The bad news is that while the average couch potato would be chock full of body fat, they tend not to find themselves at the ends of the earth on an expedition — or even on a hiking trip gone very wrong. So the best-case-scenario in our worst-case scenario is that your rabbit-chasing bro does stumble off a cliff because that’s good for the remaining folks, since his organs and muscles haven’t wasted away entirely from lack of eating, and what you want most of all is his fat.

Are we done here, please? Not quite.

There’s the matter of preparation. To cook or not to cook. Believe it or not, it may not be necessary, depending on where you’re stuck. Human organs are sterile and as long as whatever tools you used to open a person up weren’t massively laden with bacteria, you’d be fine eating someone’s innards entirely raw. Schwartz says that even the meat, the muscle, wouldn’t necessarily rot. Innuit would bury whale and seal meat in the tundra where it would freeze and desiccate and that the same thing would happen in a dry, desert environment. In a humid climate you would have to fear putrefaction, but if the initial point is to gain the nutrition to live another day, building a fire isn’t necessary. It wasn’t for survivors of The Essex, nor for members of the Uruguayan rugby team stranded in the Andes after a 1972 plane crash killed most of their party. They were able to eat their killed compadres raw, who were preserved by the cold.

Yes, now we’re done, if not done for. Bon appetite!