Here I will talk about the digestive system of my Kepler Bb humanoids.


The teeth are much stronger than bone(Strong enough that they can eat bones no problem). Other than that and all time tooth formation(so a loose adult tooth is no problem for them since another will grow in its place), they are pretty much human in the mouth.



Not much difference here besides length and time it takes for food to go down the esophagus.



This here is where it differs the most. There are actually 2 stomachs connected to each other but they each have different roles.

The first stomach is the one most likely to get infected and is where chemical and mechanical digestion take place.

The second stomach is less likely to get infected and is used as an antinausea defense. If the first stomach is too full, only a little bit of food goes to the second stomach. If the first stomach is infected, all the food goes to the second stomach. Here only chemical digestion takes place.

There is a sphincter that separates the 2 stomachs which I call the gastric sphincter. This is why food doesn't always go into the second stomach. enter image description here

In the second stomach, once it gets full enough it starts pushing the partially digested food into the first stomach which then lets it through bit by bit into the intestines.

The liver, gall bladder, and pancreas are just like the esophagus in that there is little to no difference.


Here there are some differences. For 1, the small intestine has even more absorptive surface area than ours. Second, there are glands in the small intestine that secrete their own digestive juices. The large intestine has a longer appendix that isn't useless at all and won't burst simply from inflammation. So a humanoid can have appendicitis several times in its life without an appendicular rupture(rupture of the appendix). Other than that, the large intestine, rectum, and anus are just like ours except for size.

I will draw the whole digestive system in different states later but don't be surprised if it is a bad drawing. I am horrible at drawing the intestines.

Anyway, is it useful to have this gastric sphincter and second stomach as an antinausea defense and to have the second stomach push stored food into the first stomach instead of pushing it directly into the intestines?


Here are a few pictures of their digestive system(Liver, pancreas, and gall bladder not included):

GI tract StomachBonesDuodenum

You see how bad I am at drawing the intestines? None of these drawings are to scale.

  • 1
    $\begingroup$ Have you looked at the Ruminants, like cows? When exploring alternate physiologies, I find it very helpful to look at prior art from other species. Also, what environmental concerns on Kepler Bb make a single stomach so ineffective that it's worth spending twice the resources to have two of them? $\endgroup$
    – Cort Ammon
    Sep 20, 2016 at 18:15
  • $\begingroup$ It isn't so much the environment as it is genetics. I guess it is partly environmental as well. In prehistoric times, vomiting food was so not useful for them. Those that did starved to death. However some people naturally didn't throw up as much. They still threw up food though. Over time they evolved a second stomach and gastric sphincter to prevent the throwing up of food. At first it was only for this purpose but then later on it became useful for food storage and now this is quite important for morphing powers and is still a good antinausea defense. $\endgroup$
    – Caters
    Sep 20, 2016 at 18:29
  • $\begingroup$ Vomiting happens to eject the toxic substances in the stomach. How does the second stomach improve on this? Does it filter toxins and/or kill bacteria in a way the first stomach can't? $\endgroup$
    – Cyrus
    Sep 20, 2016 at 18:31
  • $\begingroup$ But vomiting food that is useful simply because the stomach is overfull or it is infected to me isn't useful. I mean it works but it also predisposes a human to dehydration and starvation. Having the second stomach there prevents food from being thrown up. However, it doesn't prevent the throwing up of viruses, bacteria, gastric juices, and bile. Those still get thrown up but the food is safely stored in the second stomach where chemical digestion can continue peacefully until the nausea and vomiting stops. $\endgroup$
    – Caters
    Sep 20, 2016 at 18:39
  • $\begingroup$ @Caters Is the environment toxic enough to warrant the costs? Consider the energy costs. Every minute where you're not in the process of vomiting (a very bad behavior... you don't want this to consume many of your minutes), you're lugging around the mass of an extra stomach. Can you find an advantage to the split stomach which benefits the creature in good times? Like how Ruminants use the first stomach to aid in digestion of food they could otherwise not consume. That helps balance out the cost of an organ. $\endgroup$
    – Cort Ammon
    Sep 20, 2016 at 18:43

2 Answers 2


Throwing up is actually a useful biological mechanism, because it expels toxins, bacteria and the like.

Herbivores, like horses often die from colic and if they are poisoned, you actually have to mechanically flush their system. (I grew up on a farm, which is why I have this info).

The fact that horses can't puke is actually a leading cause of death for them.

Things such as drinking alcohol are right out, because the likelihood of being poisoned (it is a toxin after all) goes up very, very much. There are lots of animals that can't vomit Included on this list are small mammals, whose quick metabolism and rapid birth rate mean that they aren't going to live long anyhow, and they would absorb any poison fairly quickly anyway.

Judging from the structure of the teeth, and that these are going to be intelligent, like humans, this tells me that they are omnivores. There are omnivores with multiple stomachs, but generally, their diets consist of mostly plant matter, with the ability to eat meat if need be.

However, you might want to consider brain development, which is very much supported by a diet consisting of meat. The double stomach implies a diet mostly of plant matter.

I see that you've said throwing up CAN happen and "it doesn't prevent the throwing up of viruses, bacteria, gastric juices, and bile." But, here's the thing, being nauseous is mostly a product of those mechanisms, and things like motion sickness and puking from over-indulging are part of that package. throwing up from over-indulgence and getting dehydrated as a result doesn't happen a lot in our species, and our single stomach can actually stretch an amazing amount.

Now, if stomach #2 is good at filtering out bacteria/infection/poison or releases something needful when that happens--then, ok. We can throw up because the lower esophageal sphincter allows us and a barrier isn't created. If it's a special stomach specifically for bones, it would separate those down. Here's a little something on bone digestion, dealing with the high PH needed and talking about a type of vulture that does, on the regular:

Bone is an extremely indigestible material, being essentially an organic limestone, calcium hydroxyapatite. If you were to eat large bone shards, you’d probably tear your intestinal lining before you extracted much of its nutriment. Very few animals eat bone because few animals have any reason to. Almost alone in the animal kingdom, the Osedax polychaetes, or boneworms, digest the bones of whales that have fallen into the abyss — a phenomenon rare enough to warrant its own term, “whalefall” — scraping out whatever fats they can from between the ossicles; like writhing flowers in long planting boxes, there are gardens of these in the graveyards of the deep. Hyenas will eat bone, but it doesn’t make up a significant part of their diet. Lammergeiers, on the other hand, have a diet that is 90% bone; they will even eat owl pellets, which contain the swallowed bones an owl couldn’t digest. Lammergeiers have solved the problem of bone digestibility by creating incredibly caustic gastric acid. Human gastric acid remains between pH 1 and pH 1.5, while a Lammergeier’s stomach registers around pH 0.7, making it close to pure hydrochloric acid. Add to that an extra-long intestinal tract and a lifestyle of effortless gliding, and you can see how the birds make a living out of eating bone. To get to the rarest and most succulent meat on the cow, a Lammergeier has a stomach that can dissolve almost anything. LINK

I did find a great article on humans and bone digestion, wherein scientists ate a shrew, whole and then sifted through their poop.

I also found something on cavemen and primates and bone digestion. This implies that while we ate bone, finding so many fragments undissolved means that we are not terribly efficient at it.

  • $\begingroup$ isn't bone itself alkaline from all the calcium and phosphorus? So for digestion of something alkaline, wouldn't acid like our gastric acid do a better job than a base and acid + enzymes even better? $\endgroup$
    – Caters
    Sep 21, 2016 at 13:49
  • $\begingroup$ The pH scale is a measure of the hydrogen ion concentration. It spans from 0 to 14 with the middle point (pH 7) being neutral (neither acidic or basic). Any pH number greater than 7 is considered a base and any pH number less than 7 is considered an acid. So the Lammergeir's PH of POINT .7 is less than 0, meaning it's highly acidic. $\endgroup$ Sep 23, 2016 at 3:37

If your species are herbivores, due to difficulty in digestion, two stomachs can be justified. After all leaves and bark contain cellulose which is quite tough to digest. But then it is hard to justify canine teeth and high intelligence. High intellect is a sign of omni or carnivore as herbivores do not need intellect to hunt or find food sources as well as cannot get enough calories to justify an energy hungry brain.

A second option might be some sort of alien food that is hard to digest but high in calories.

The problem with evolution is that every step should be better than previous step or your chances of getting that final case would be minimal. So your animals should recently turned omnivore and obtained high intellect and haven't lost their second stomach yet.

  • $\begingroup$ Why couldn't it be a different way? Couldn't it be that they started off with an energy hungry brain and only 1 stomach but genetics and environment made it so that they had to store food somehow when they were nauseous and then as a result, they evolved a gastric sphincter and a second stomach for that purpose? $\endgroup$
    – Caters
    Sep 20, 2016 at 18:45
  • $\begingroup$ It is easier to store food as fat. More calories and it protects from external damage. $\endgroup$ Sep 20, 2016 at 20:28
  • $\begingroup$ That may be true when it is fully digested but what about when it is still in the process of digestion? $\endgroup$
    – Caters
    Sep 21, 2016 at 1:18
  • $\begingroup$ If your species needs to digest more food at the same time, they could have larger stomachs. If you really want to go this road, I would suggest going with hard to digest high calorie alien food. Something that will break down into fats and sugars but needs work. Say some sort of alien life form made out of complex fat-carbohydrate combination that is quite tough to digest. Make those organisms to hide so that intellect would be a must to have them as food source. $\endgroup$ Sep 21, 2016 at 6:22

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