11
$\begingroup$

In this story, set sometime in the future, most farm animals have gone extinct due to diseases. I remember reading somewhere that the average human has around 100 thousand calories, meaning that one human could last for about 50 days.

In a world where humans die very quickly so a lot of humans are born to compensate, could eating dead humans be sustainable for a population of about 5 billion? If not, what other items on such a planet would help support humans?

$\endgroup$
11
  • 9
    $\begingroup$ This seems (as phrased) to break physics, i.e. it takes more energy than 100,000 Cal to make a human, the population wouldn't be sustainable as-is. Do you mean to ask about dietary deficiencies from a "long-pig" diet? $\endgroup$ Commented Mar 10, 2022 at 22:16
  • 2
    $\begingroup$ Well @EveninginGethsemane not really physically sustainable I agree, but for some special occasions it may be appropriate to have a sustainable tradition.. suppose you get married.. you could decide to have a celebration ritual to serve your mother in law for dinner :p $\endgroup$
    – Goodies
    Commented Mar 10, 2022 at 22:20
  • 1
    $\begingroup$ @Tortliena oop, ok thanks :D $\endgroup$ Commented Mar 10, 2022 at 22:53
  • 1
    $\begingroup$ Alright thank you; was about to ask the reason for the rollback $\endgroup$ Commented Mar 11, 2022 at 0:47
  • 1
    $\begingroup$ Of course, Randall Munroe has already tackled this question in his XKCD page: what-if.xkcd.com/105 $\endgroup$
    – Vorbis
    Commented Mar 13, 2022 at 18:29

11 Answers 11

43
$\begingroup$

No.

What you're trying to accomplish is a perpetual motion machine, just with cannibalism. Over the course of their lifetime, a human will consume 50-100 million calories. As noted, their corpse will only give about 100,000 back, meaning that 98+% of the energy is lost. Even with a shorter lifespan, humans will not break even. Energy is lost through heat and action, and that's energy that cannot be recovered.

Oh, and biomass loss. Humans constantly exhale carbon dioxide, losing carbon that used to be biomass. That lost biomass can no longer be used. If you took as a whole the mass of humans, it would have to shrink if they fed on themselves. Sweat, urine, and feces would be other sources of biomass loss.

So what should they actually eat?

Plants and mushrooms. Plants need to be involved in any stable food chain. They are really the only way to efficiently add energy into a food chain. They convert carbon and other inorganic materials into biomass for consumers, as well. Mushrooms will do similar.

$\endgroup$
9
  • 6
    $\begingroup$ 99.8%, not 98%. $\endgroup$
    – benrg
    Commented Mar 10, 2022 at 22:26
  • 1
    $\begingroup$ +1 for a good succinct argument. I still find it grimly hilarious that the Breatharians claim that the carbon dioxide exhalation argument is invalid. $\endgroup$ Commented Mar 10, 2022 at 22:28
  • 8
    $\begingroup$ The question says "farm animals" went extinct. As per Demolition Man, there are other fine meats on the menu. :) $\endgroup$ Commented Mar 10, 2022 at 22:34
  • 2
    $\begingroup$ Eww, mushrooms are gross! $\endgroup$
    – Tom
    Commented Mar 10, 2022 at 22:34
  • 5
    $\begingroup$ @U.Windl: Mushrooms are less efficient than direct consumption if humans could eat what the mushrooms are feeding on. But a lot of what mushrooms are feeding on is inedible (or at least unpalatable) to humans (e.g. wood, leaf litter, manure/feces, straw, cardboard, coffee grounds). If the original substance was toxic or had little/no human-digestible nutrients, and the mushroom can convert even a few percent of the stored energy to human food, it's worth it. Large-scale plant farming will produce tons of inedible by-products (e.g. raise grain, get straw), so the mushroom food is "free". $\endgroup$ Commented Mar 11, 2022 at 14:20
10
$\begingroup$

This works for most livestock because you can feed a cow (or just about anything else) food that wouldn't be nutritious/palatable for a human.

If you have to feed your livestock humans something to fatten them up (and wow, it takes up to 20 years before they're ready for slaughter!), then you could just feed that directly to the non-livestock humans and save the trouble.

Compare this to cattle, where you can feed them grass and other plants with zero (human) nutritional value. Chickens can literally peck around eating bugs and what not. Pigs will eat very nearly anything (table scraps, offal, murder victim corpses you want to dispose of).

Though we often do feed these animals with stuff that humans could also eat, this only speaks to how abundant food is today in the 21st century, that we can spare that to fatten up livestock more quickly.

Cannibalism economics only works when you've got a high population that you want to make smaller, and only for the duration of the "thinning of the herd". Perhaps afterward, if some have developed a taste for human flesh, they might keep human-livestock at great expense... but it will have stopped making economic sense long before that.

Counterpoint: Such people (not sure that's the right word here, bear with me) might go so far as to genetically engineer or breed human-livestock that was more economical, but such a project would require long term effort.

$\endgroup$
7
$\begingroup$

Mummies.

mummyvores

source

Your world has a surfeit of human mummies. Maybe the weaponry that caused the demise of these people sterilized the vicinity and they dried out into mummies. Maybe they were frozen by the nuclear winter. Maybe they fell into hypersaline lakes? Or were put there? Maybe the dead were collected and preserved for food.

In any case, they are many. When alive these people were not cannibals - they ate at Wendys and Arbys like people do. Now their mummies preserve some of their caloric value to sustain your people.

It is not a super long term plan. It will be sustainable as long as your mummy supply holds out.

$\endgroup$
3
  • $\begingroup$ +1 fully agree.. mummies are delicious.. you can cut them into cookies etc.. $\endgroup$
    – Goodies
    Commented Mar 10, 2022 at 22:45
  • 8
    $\begingroup$ @Goodies I prefer mummy shaped cookies than cookie shaped mummies. $\endgroup$
    – DKNguyen
    Commented Mar 11, 2022 at 0:20
  • 1
    $\begingroup$ Mummies? More like. . . yummies. . . . $\endgroup$
    – Daron
    Commented Mar 11, 2022 at 17:39
6
$\begingroup$

The Net Energy Doesn't Add Up:

Entropy means everything goes from a high energy state to a low energy state. So as humans are born and live, they consume energy. Without energy inputs, a given mass of humans would only go down in energy, so a source of energy to add to the system is essential. While you could maintain a population for a short while by steadily reducing the number of humans, eventually, the energy would get lost and there would be no more.

So you need a source of external energy (at LEAST a few plants, who can gather energy on their own) to provide the energy fuel needed to keep the energy cycle running. Enough plants to maintain an oxygen cycle would be needed, and someone would need to crunch some numbers about if that is more or less than the number for food production. There would be serious long-term nutrient and prion issues with a predominantly human-flesh-based diet (even if most of the nutrients could be recycled) that would requires some vitamin and mineral inputs to allow more human biomass to be produced. A few genetically engineered yeast might be able to carry out this function.

Long-term, you probably want a simple cycle of food production with people eating plants and fungi/yeast, and using human flesh to provide the fertilizer to grow those organisms. That way, you avoid what would rapidly be a massive spread of prions causing a lot of nasty degenerative diseases.

$\endgroup$
3
  • $\begingroup$ Prions, in particular, are a massive problem even for small-scale cannibalism. To the best of my understanding, there is no known way to decontaminate meat which has been infected with prions, without rendering it totally inedible. Worse, Wikipedia claims that around a million people worldwide are infected with Creutzfeldt-Jakob disease per year, and there is a specific, documented instance of prion transmission between humans via cannibalism. It's not a solvable problem. $\endgroup$
    – Kevin
    Commented Mar 11, 2022 at 7:29
  • 1
    $\begingroup$ @Kevin: In fairness, in the case of Kuru, it happened much more easily because their particular style of cannibalism included consuming the brain, and because it was cyclic; the young cannibalized dead family members (mostly elderly), who in turn were cannibalized by their own descendants. While it's possible for spread to occur from eating other tissues, it's much lower rate. And if you split society into cannibals and the cannibalized, with no role reversals, spread is naturally limited; even if the person being eaten has a prion disease, it stops with the people who eat them. $\endgroup$ Commented Mar 11, 2022 at 18:03
  • $\begingroup$ To be clear, not saying large scale cannibalism is practical. Just saying prion disease problems can be mitigated. It still remains the case that living off dead humans would only provide a tiny fraction of the total caloric needs of humanity (you'd need the population to contract by a factor of 1000 or more per generation, assuming you could preserve all the dead indefinitely for future consumption). $\endgroup$ Commented Mar 11, 2022 at 18:07
2
$\begingroup$

Recycling human flesh for food would reduce, but not eliminate the other food input that the human society would need. So it could be supplementary but you would still need food input from other sources, albeit in reduced quantity.

Which is why some animals eat their young in times of hardship (or if the young die). The young are going to die anyways in times of hardship so better to not let the nutrition go to waste.

Like regenerative braking on a car. You can't run continue to run forever solely with the power reclaimed from regenerative braking, but you can reduce the fuel consumption.

So yes, it provides nutritional value, but not indefinite nutritional value.

$\endgroup$
2
$\begingroup$

I wanted to mention that cannibalism leads to Creutzfeldt-Jakob Disease. I'm not a microbiologist so I'm not fully familiar with the process, but eating meat of one's own species leads to the creation and concentration of 'prions' which cause the disease.

It's what caused the 'mad cow disease' (BSE) crisis in the 90s - farmers were feeding beef and cow bone meal to cows to boost their protein intake.

Instances of CJD also arise in small tribal communities, such as those in Africa, that engage in cannibalism (and yes, cannibalism is still practised in some parts of Africa today, even though it's illegal).

So no. For the long-term health of the population, it is not a good idea.

$\endgroup$
1
$\begingroup$

This can not be sustained

No math is needed to tell you that anything at all that has any kind of waste, and only eats itself, will reduce to nothing. Consider your people like a swimming pool above the ground. After all, this is just about adding and removing calories. People are like a swimming pool

Let’s assume your people are like us and they use the toilet, and they breathe, and they have body heat. Those are all calories. Calories leave one human, so they leave all humans. Let’s call calories “water” for now so it fits the pool picture. All of humanity on your planet is “the pool,” and the amount of calories in all of humanity is the water in the pool.

OK, like I said. People make heat, they use toilets, and the breathe out. So that happens for billions of people. The number doesn’t matter, but it’s a leak in the pool. It’s calories leaving humanity somewhere. It can be a big leak, or a small leak, it doesn’t matter at all.

OK, so water is coming out of the pool now. Maybe fast, or maybe slowly.

Now let’s feed all your humanity. It doesn’t matter how much or little they eat, they all eat the same thing. They eat the water in the pool: they eat themselves. The calories come from humanity. So now, you are taking water from the pool, and putting it into the pool. You see? The number doesn’t matter. If you take 200 gallons from the pool and “eat it” so 200 gallons go into the pool, you didn’t add anything at all. Try 300 trillion gallons? That’s a lot of water. But that’s fine, because all those people will be eating it up again—all 300 trillion gallons of it. Did the pool get any bigger? Any smaller?

Well, it is getting smaller. You have a leak, and you are adding no water at all from outside. Water goes out, no water goes in, pool empty. Everyone dead. It ends the same with every number.

Is there any nutrition?

There is nutrition. What type depends on what you ate. Some diets will make you have more fat, some more protein, and some will have very little value. There is no difference what livestock you use, you get out what you put in. Human nutrition has the same variety as any other animal. A liver has more iron. Bones have calcium. Etc. There is nothing really unique about a human diet that can’t be done with another animal just as easily. And like any other animal, you can change the nutrition by changing what the animal eats and drinks (clean water is essential).

You will have no scientific justification for eating human flesh, it will need to be some mystical thing like vampires to be believable.

$\endgroup$
4
  • $\begingroup$ I would think that extremely strained food resources would be a scientific justification. $\endgroup$
    – DKNguyen
    Commented Mar 11, 2022 at 0:29
  • 1
    $\begingroup$ @DKNguyen That doesn’t change the way it ends. It will end with one person figuring out how to eat themselves. $\endgroup$
    – Vogon Poet
    Commented Mar 11, 2022 at 0:36
  • $\begingroup$ Are you answering the edit? Your answer came after the edit so I assumed that's what you were answering which doesn't talk about eating only people for food. $\endgroup$
    – DKNguyen
    Commented Mar 11, 2022 at 1:26
  • $\begingroup$ I have no idea, I only looked at it once. $\endgroup$
    – Vogon Poet
    Commented Mar 11, 2022 at 1:41
1
$\begingroup$

You might want to consider the "business proposal" that was floated several times in the early 1900s. The plan was to establish a Cat Ranch and a Rat Ranch adjacent to each other.

“To start with, we will have about one million cats. Each cat will average twelve kittens a year. The skins run from ten cents each for the white ones to seventy-five cents for the pure blacks. This will give us twelve million skins a year to sell at the average of 30 cents apiece, making our revenue about $10,000 a day gross.

“A man can skin fifty cats a day, at two dollars, and as it will take 100 men to operate the ranch, therefore, the net profit will be about nine thousand eight hundred dollars a day.

“We will feed the cats on rats. The rats multiply four times as fast as the cats. If we start with one million rats, we will have, therefore, four per day for each cat.

“The business will be self-supporting and automatic all the way through. The cats will eat the rats, and the rats will eat the cats, and we get the skins. Awaiting your prompt reply, and trusting that you will appreciate this opportunity to get rich very quickly.”

$\endgroup$
1
$\begingroup$

Sometime around 1971, Professor Pat Doyle of the math department at Michigan State University wrote a paper in which he used the standard predator-prey equations, merging the predator and prey variables. The result was a paper with a title something like "An in-eating cannibalistic society could be stable".

Someone in the math department might be able to come up with a copy. It was published in an in-house journal.

He did it as a joke, I think, but the math was serious.

$\endgroup$
0
$\begingroup$

Laputan and Matrix technology

You have more than human flesh to work with. Laputa's finest scientists have developed machines which are capable of reversing the process of digestion...

an operation to reduce human excrement to its original food, by separating the several parts, removing the tincture which it receives from the gall, making the odour exhale, and scumming off the saliva.

Of course, the more astute physicists here have noted you can't have something for nothing. However,

The human body generates more bioelectricity than a 120-volt battery and over 25,000 BTUs of body heat. Combined with a form of fusion, the machines had found all the energy they would ever need.

$\endgroup$
0
$\begingroup$

In terms of food consumption labels, 1 calorie is actually equal to 1 kilocalorie.

The term calorie is defined as the amount of heat generated when a material is burned.

How much of that energy can be converted by the human body depends on the composition.

Fiber has a lot of calories, but null nutritional value, since the digestive tract cannot process it, as does the methane gases in the lower intestine: high calories, zero nutritional value.

The same goes for much of the human body...high calorie, but inedible.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .