On this planet there are two species of alien humanoids creatures , one group evolved an omnivore based diet and the other has a semen based diet, both groups are bipedal and share a common ancestor.

I'm trying to figure out what type of evolutionary factors and genetic changes could have lead this group of humanoid creatures on this planet to evolve a diet based out of semen. I'm using the vampire bat as an example of creatures that have switched from a solid to a fluid based diet.

one of the obstacles for vampire bats was developing a digestive system that allowed them to excrete large amounts of metals such as iron. Could the same be applied to these humanoid creatures?

what type of biological changes needs to happen for a semen based diet?

How much semifinal fluid would these aliens need to survive?

How will they manage to survive with this diet?

since their primary source of food is fluid based , how would it effect their jaw and teeth?

  • $\begingroup$ A few issues here. First, congratulations on asking the question in an objective, unobjectionable (to me) mannner. However, it is required that there is only one question per post. A good answer is likely to include some of the points relating to your sub-questions, but others, such as "How long did it take them to diverge..." would need to be asked as a separate post. So I would suggest removing all the sub-questions from your answer to avoid this question being closed. $\endgroup$ May 11, 2023 at 0:43
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    $\begingroup$ Is it one species feeding off of the other? For obvious reasons, the species can't feed solely off of itself because at that point there are no outside nutrient inputs and they quickly starve. Large herbivores on Earth produce impressive amounts of ejaculate, and if this were to satisfy nutritional needs, a smaller organism might be able to survive in that manner exclusively. But there is a tight ecological balance to be had, as any aggressive population growth would likely lower the fertility of the species they fed upon to the point of catastrophic extinction. $\endgroup$
    – John O
    May 11, 2023 at 15:08
  • $\begingroup$ Obviously there are some pretty weird restaurants in your story. $\endgroup$
    – Boba Fit
    May 11, 2023 at 15:29
  • $\begingroup$ you may note vampire bats feed on animals many many times larger than themselves to get enough calories from a meal. $\endgroup$
    – John
    May 12, 2023 at 0:02

1 Answer 1


Frame Challenge

My Testicles are sore just contemplating how much ejaculate one would have to produce, in order to provide a substantial meal. If we go for the high-end of Calorie listing for a single 'serving' - that's 25 Calories.

An average Man needs to consume 2,500 Calories a day.

That's 100 'servings' that you would need to feed a Humanoid in a day.

Assuming it's voluntary, that's still not very efficient. Anecdotally, FWIW - after 4 in a short space of time, we are getting into the 'This is no longer fun' zone.

Even a Mosquito type solution where the fluid is drained without knowledge or against the will, it's still a problem of proportions.

Then there is the next pretty significant biological problem:

You are limiting your food source to 50% of the population

You might argue that Mammals do this for their young, requiring Mothers Milk - which is a good argument to start with - the problem is that firstly the amount of production differs vastly and secondly Young mammals are only on the teet for a small percentage of their lives and they are relatively small (meaning, despite growing, they aren't requiring as high a calorific intake as an Adult)

In order to make this viable, you would have to have some species that is constantly secreting this fluid, almost like Sweat and at a rate where it could be harvested non-invasively to provide sustenance.

To make it believable - I would add something like the species that ingests the fluid have a critical role in the reproductive cycle (think how Chilli seeds are deposited by birds)

  • $\begingroup$ Why do you say that they are limiting the food source to 50% of the population? Humanoid does not require that there are equal numbers of each sex, far more likely that this would evolve if ratio of males:females is 10:1 or higher, with females more like queens of insect hives. $\endgroup$ May 12, 2023 at 7:50

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