16

I'm designing a creature that is supposed to be able to eat "basically anything", within the realm of plausibility for what is essentially an organic creature. Its digestive system can be as complicated as necessary, and evolutionary history is not an obstacle, the creature could be either alien or engineered but one way or another it is omnivorous to the extreme.

At the very least, it should be able to break down any organic, energy-storing molecule, ranging from plants and meat to fossil fuels. Any other naturally-occurring chemical with a high energy content should be edible as well, if possible.

Notably though, it is an active, mobile animal so it should only be interested in eating things that have a relatively high energy content. It is possible to get energy by oxidizing metal but probably not enough to sustain a high-energy lifestyle.

How would the creature's digestive system work, in order to give it the ability to digest as many different things as possible?

SRM
  • 25,402
  • 4
  • 43
  • 113
IndigoFenix
  • 29,066
  • 3
  • 69
  • 120
  • 3
    Digestion can be fairly simple and straightforward. The real challenge is not being poisoned by all sorts of foreign proteins or isomers. This thing needs to break everything down and synthesize its own aminos, for instance. But in the meantime it needs to make sure none of the foreign ones come in contact with its own cells... probably some mineral-based lining to its digestive organ (like teeth). – John O Jan 28 '20 at 15:49

6 Answers6

19

At the very least, it should be able to break down any organic, energy-storing molecule, ranging from plants and meat to fossil fuels.

The closest thing we got on Earth are roaches. They will eat anything that they can chew.

Digesting fossil fuels is complicated because of a few factors:

  • Breaking them down within your body could lead to the formation of carbon monoxide, which is terribly poisonous;
  • They are rare enough to find in natura that most creatures had no evolutionary pressure to develop the means to break them.

That does not mean animals do not consume them. Many herbivores, ranging from elephants to deer, and also some omnivore apes will eat charcoal. They consume it not as an energy source, but as a natural antidote for toxins in their diets (the article cites monkeys only, but there is evidence for other animals).

So let's start from our best bet. You could have an evolutionary story where roaches have a symbiosis with these two bacteria:

These bacteria could live in the gut of the roach. In return for giving the roach part of their energy output, they have an environment where they can thrive without competition. Also the roach will provide them with the raw materials they need to live, so they don't need to bother about getting food. A similar process happens with termites and bacteria in their gut - termites don't break down the cellulose they eat, the bacteria in their gut do.

So there you have it. Imagine a world in which roaches could eat plastic and oil. If you had a roach infestation in your house, they could drink your car's gas and then eat the fuel tank as a dessert.

The Square-Cube Law
  • 141,440
  • 29
  • 264
  • 586
  • 1
    Humans do this too; our intestines can only absorb the most basic of nutrients, but they are inhabited by a variety of bacteria that digest complex foods into what we need. In return for this valuable function, we provide them a steady food supply and a nice, safe home. Making more foods edible is just a matter of finding (or engineering) new bacteria that can digest more things for us. – StephenS Jan 29 '20 at 18:59
12

I would suggest giving it multiple stomachs, like cows, however here each stomach has a different function: one for degrading meats, one for fibrous plants, one for fruits, etc. This would probably require a first stomach with some kind of filtering method, or at least something to break down tough foods, so that each subsequent stomach can fulfill its role properly.

It could also be interesting to give this animal a complex internal microbiota. A lot of micro-organisms are much more effective than we are at breaking down energy-storing molecules, and having the appropriate bacteria and fungi in each stomach pouch would give your animal an incredibly wide selection of foods to live off of.

Whitehot
  • 2,569
  • 6
  • 21
  • 2
    A stomach full of symbiotic chemoautotrophs for the more stable fuel sources... How wonderfully combustible. – Joe Bloggs Jan 28 '20 at 13:22
  • 1
    @JoeBloggs Tremendous methane outputs! You'd think twice before hunting this beast with a rifle ;-) – Whitehot Jan 28 '20 at 13:24
  • @Whitehot Methane is a fuel source... wouldn't the creature necessarily have to have a way to digest the methane also? I.e., combust the methane and draw energy from it? – SRM Jan 28 '20 at 13:45
  • Multiple stomachs or multiple mouths... it might be easier, rather than a chemical sorting system in Stomach #1, to have the creature ingest the foods using the most appropriate mouth. Then the brain could be involved in making the routing selection. – SRM Jan 28 '20 at 13:47
  • @SRM Good point concerning methane! Although it would probably need to be a microorganism that degrades it, I'm struggling to imagine that an animal intestine would be able to perform such a feat. – Whitehot Jan 28 '20 at 13:58
  • @SRM Even if the beast did have multiple mouths, it would be challenging to separate food categories efficiently if you're a true omnivore. Wouldn't a fish's bones, scales and meat need to be ingested through different mouths? – Whitehot Jan 28 '20 at 13:59
  • 2
    @Whitehot Maybe a fish goes to the same place. But slurping a pool of oil might not. I'm suggesting that some of the more exotic substances might deserve unique orifices. – SRM Jan 28 '20 at 14:04
  • 3
    @SRM: if the methane is routed from multiple stomachs to the dedicated ‘high energy gases’ stomach, then the creature can really digest efficiently. Sorry, did I say digest? I meant explode. – Joe Bloggs Jan 28 '20 at 14:19
  • @joebloggs :-) I recognize the difficulty. But if this is going to be the ultimate omnivore, we should at least consider ways to make the methane digestible. Do we have any questions on WB about powering organic creatures via combustion? Seems like I recall some I’ve asking about that a couple years ago. – SRM Jan 28 '20 at 14:26
  • Maybe it doesn’t need to digest methane, merely use it for locomotion. See design of “jet dragon”: https://worldbuilding.stackexchange.com/questions/9020/is-a-rocket-dragon-possible/9023?r=SearchResults#9023 – SRM Jan 28 '20 at 14:50
  • 1
    Ooo! Check this out: https://worldbuilding.stackexchange.com/questions/154285/ecology-with-methanogenic-respiration/154288?r=SearchResults#154288 – SRM Jan 28 '20 at 14:55
  • @SRM Perhaps our super omnivore also absorbed some alien chloroplasts while it was evolving? https://en.wikipedia.org/wiki/Elysia_chlorotica – Whitehot Jan 28 '20 at 15:24
5

Heat differential engine.

Your creature oxidizes molecules in its "stomach" which is more of a furnace. Anything that can be oxidized is fair game - any reduced carbon, or nitrogen, or metal salt. Oxidation produces heat. The amount of heat produced is controlled by controlling oxygen ingress to the stomach.

Under hot conditions, certain metalloproteins change configuration. The circulation brings these proteins into hot conditions near the stomach and they capture heat energy with the configuration change. When the hot-configured metalloprotein circulates out to the cold exterior (possibly radiator plates or fins) it shifts back to the cold configuration. This conformational shift is linked to an ATPase and generates ATP for the creature to use for its muscles and metabolic processes, as Earth life does.

Willk
  • 304,738
  • 59
  • 504
  • 1,237
  • It sounds like you would need very fine tuning of the heat of your furnace for this to work. Do you know of any animals that can tune their oxygen intake this finely? – Whitehot Jan 28 '20 at 14:39
  • 2
    @Whitehot: I am such an animal and unless you are a robot you are too. Oxygen capture in the lungs and subsequent delivery to tissues is tightly regulated according to metabolic need of those tissues. Oxygen is toxic stuff and you only want the amounts you can use floating around your delicate biology. If you are a robot I guess your secret it not safe with me since I just outed you; sorry. – Willk Jan 28 '20 at 14:46
  • I do understand the transmission of oxygen throughout a metazoa- I mean, my body, but this involves a whole number of very finely tuned enzymes circulating in blood. In my mind the furnace that you propose function with gaseous exchanges, but I may have misunderstood how it functions exactly. Could you describe your stomach-furnace in a little more detail maybe? :) – Whitehot Jan 28 '20 at 15:21
  • I was thinking of using heat, but how efficient is using heat compared to utilizing chemical energy directly? As far as I know, no living organism uses heat differentials as its primary power source, and given how easy it is to produce heat by breaking down organic molecules you'd think that something would make use of it, yet heat production seems to only be used for homeostasis in living things. – IndigoFenix Jan 28 '20 at 15:54
  • @Whitehot: Air control might be like a damper in a steam engine. The firebox of a steam engine has fuel intake and air intake, and you can reduce the air intake using the damper, which reduces the heat. I envision the "firebox" in this creature to work along the lines of the heating of a wet haystack. http://www.todayifoundout.com/index.php/2014/09/moist-baled-stacked-hay-catch-fire/ – Willk Jan 28 '20 at 15:55
  • @IndigoFenix - I do not know of any such organism either. I here assert that this has to do with the difficulty of culturing and studying archaebacteria that live in extreme environments where harnessing a heat differential across a small body would be possible. Pretty much anyplace on earth where there is an energy differential to be harnessed there are prokaryotes harnessing it. – Willk Jan 28 '20 at 16:01
  • In that case the control of oxygen in your furnace is physiological, not biochemical. Very different, and I doubt that it could be anywhere as fine tuned as the oxygen intake is at the cellular level. – Whitehot Jan 28 '20 at 16:05
  • @Whitehot, whitehot… whitehot. If your respiration rate increases and your arteries dilate to supply your muscle with more oxygenated blood in response to their lactic acid production, is that physiological or biochemical? It is both - an integrated system for us and I here assert for this heat eater as well. It is easy to imagine physiologic regulators governed by the circulating relative % of hot and cold isoforms of the above described protein. – Willk Jan 28 '20 at 16:24
  • @whitehot - I am thrilled by the way that this humble scheme has prompted any thinking on the part of you or anyone else! – Willk Jan 28 '20 at 16:36
  • @willk We do use both physiological and biochemical regulation, and this creature could do too. But I'm not quite grasping what medium your furnace contains. Are the reduced carbons in a bath of digestive enzymes? Or are they exposed to air, and burning actively? I am very interested in your proposal, it's a fantastic scenario to imagine, but you're not getting my upvote until I'm thoroughly convinced that this would be viable in vivo ;) – Whitehot Jan 28 '20 at 17:46
  • @Whitehot - take a look at the haystack link. The furnace is like a hot wet haystack. /But if the moisture is in that critical 20 to 50 per cent level, then the temperature will rise... Once it gets to around 80°C, the bacteria themselves will die.. If the haystack.. is big enough so that the outside insulates the inside where the chemical reaction is happening, then the heat is trapped... In this stage, airflow is critical. If there is too much airflow, that will remove the heat. If there's too little airflow, there won't be enough oxygen to keep the chemical reactions going/ – Willk Jan 28 '20 at 17:52
  • @Whitehot: fun thought - acetone steam engine powered by wet haystack flameless boiler. – Willk Jan 28 '20 at 18:01
  • @Willk I'm pretty sure "acetone steam engine powered by wet haystack flameless boiler" deserves its own question ^^ – Whitehot Jan 28 '20 at 21:59
  • @Willk OK, fair enough, the heat bladder seems like it could be viable, although extremely complex to set up. I'm not sure if evolution alone would allow it to exist. There is still the problem of turning the thermal energy of the heat bladder into chemical energy to be used by the body. Although heat could induce protein conformational change, I fail to see how changing back to its "cold" conformation could generate ATP, let alone generate it efficiently enough to power a cell. Protein conformational change usually uses up ATP, and quite a fair bit when heat is involved... – Whitehot Jan 28 '20 at 22:22
4

You got humans!

No, seriously - think about this.

We can eat basically anything on this big, weird world of us with proper preparation. What we can't eat right away, we can find ways to cook and make it edible. We already use stuff like coal, petroleum, and even wood. It is just a matter of time before we start making food directly out of carbon via some sort of weird 3D Food-Printer.

We already got the printers, and we aren't that far away from using carbon directly either.

Sure, it isn't directly our delicate stomachs that do this. Instead, we use our brainpower and societal resources to enable ourselves to eat whatever we think might be remotely tasty - emphasis on "remotely".

We usually think of our "digestive system" starting on our mouths, but for some foodstuffs this process happens way, way before it even hit our plates. From taming special bacteria to make cheese to using almost ritualistic processes to prepare meat, we devised thousands upon thousands of ways to make all sorts of things edible - sometimes for far longer than they should be, sometimes even if it tries really hard to kill us.

In that sense, we aren't that much different from the termite that stores special bacteria in its gut to be able to digest cellulose or from the animals that literally spit acid on top of their food to them slurp up the resulting juices. The major difference is that for them, this is the only way they have to eat.

For us, it is different. We're crafty bastards.

We don't eat with our mouths.

We eat with our brains.

So, in the end, what your creature needs isn't a super digestive system that can eat anything - instead, give them the ways to make whatever they want to eat, edible. Don't make them monster eaters. Make them monster cooks.

Mermaker
  • 8,709
  • 1
  • 28
  • 55
  • 2
    This is an oddly insightful answer. We consume all available resources -- not internally, but all in the service of our energy needs. Neat. – SRM Feb 03 '20 at 01:51
  • @SRM Thank you for the kind words, and thank you for the bounty! >.<" – Mermaker Feb 03 '20 at 13:32
0

How about having your creature be in fact a multi-combo symbiote? Maybe it's part-way through the evolutionary process of merging into a single complex being (similar to the mix of prokaryotes into eukaryotes, sort of), or maybe it's like the combo-animals of "A Fire In The Deep". Either way, its component creatures 'share' all food sources as appropriate.

Carl Witthoft
  • 1,847
  • 11
  • 13
0

Its name is "Carl"...with the iron stomach.

The mouth registers what type of "food" is being eaten. This triggers a complex neural message to glands that support the digestive process. A series of acid emitters are engaged to create the right acid mix for what is landing in the "iron gullet" this also triggers any needed mucus increases to protect the stomachs based on the acid strength. For complex or harder materials, there is a holding stomach that is designed for the full power acid and only really bizarre foodstuffs are diverted there where they get softened up before moving down to the regular stomach. For the complex gases associated with certain digestive processes, there is the ability to back-feed "burp" gases from either stomach, and the bowels "farts".

The question is for the really tough meals, is it the creature who suffers the most or those near the creature who get the brunt of the process.