Could a humanoid survive in a communal circulatory system?

Question

The Areans are a human-like species that have become wholly dependent on their technology. Most notably is their circulatory system

They float in a blood-like liquid, and instead of lungs their pulmonary vessels simply take in and excrete this fluid to the environment. The liquids are in constant flow and kept oxygenated, stocked with nutrients, and other functions needed to keep the Areans alive

Could such a communal circulation sustain the Areans? Or are there some unavoidable issues that would make it impossible?

Answer 1

I will have to answer with what @elemtilas predicted: "Could a system like this be made" because you have said that it already happened through handwavium. I will begin with some conceptual issues with the framing of this question, but in the end I hope the underlying problem asked will find an answer. Bear with me.

This question treats human blood as if it only carries oxygen to cells, but this is not true. What your system is missing is, well, a lot. But mostly, it is missing the very concept of circulation, which requires pressure differentials, which require containment. In other words, you can not do away with a closed system and a pump, and still use the word "circulation."

Veins are controlled by the nervous system to target areas of the body which need nutrients, antibodies, oxygen, hormones, etc. They also target areas where excess waste has collected, such as dead cells, carbon dioxide, toxins, etc. If you remove the closed system, you take away the nervous system's only tool for getting these provisions to; and removing these wastes from, the areas of your body which need attention.

The closed system also is the only way the oxygen can possibly reach human body cells, because once open to the air, the oxygen will be taken up and absorbed. Only be being contained in veins can the hemoglobin get oxygen to the cells as oxygen. If you design your fluid so it does not oxidize, then you have also designed it so a human cell can not oxidize with it, and killed all human cells. The thing in the fluid will not be made of human cells.

A circulatory system must be a circuit, which is in the very definition of it. A free-flowing fluid would not sustain any organism which could still be considered "human;" anything adapted to that environment would look, behave, and function in a way that would be unrecognizable as "human."

If the problem in the question is simply one of respiration, as it seems to be, and you do not want to concern the plot with buggering up all the other circulatory functions, then

the fluid you are speaking of has already been found. It is called perfluorocarbon

This is technology we are already using to replace human respiration in people who cannot use their lungs for one reason or another. It seems to fit the technical requirements of your problem, from the perspective of providing oxygen to the body.

Answer 2

Obviously

You've already established two critical facts, namely:

• The Areans are a human-like species that have become wholly dependent on their technology.
• Most notably is their circulatory system

You then tell us what this technology does:

• They float in a blood-like liquid, and instead of lungs their pulmonary vessels simply take in and excrete this fluid to the environment. The liquids are in constant flow and kept oxygenated, stocked with nutrients, and other functions needed to keep the Areans alive

The only logical answer to your query is 'yes' because you just told us that this is how they live! In other words, since this is how they actually live, there are no "unavoidable issues that would make it impossible!"

I think the likely follow-ups might be something like "Could a species with specific attributes X, Y, and Z come up with a viable technology that does M"; and "Given technology M and a species with attributes X, Y, and Z, how does the technology work?"

Answer 3

No. Consider the following points

Germs and Bacteria

The liquid is full of nutrients. So germs and bacteria will grow (like in fruit juice or even in stagnant fresh water).

Sick or Dead Humanoids

Any sick humanoid will secret germs and bacteria thus spreading the disease.

When a humanoid dies, its body will be absorbed by the liquid. If it was already sick, the sickness will spread.

Nutrient requirements

Same nutrients don't benefit everyone. Different nutrients are required

• at different ages
• under different health conditions
• under different working conditions
• at different temperatures

Multiple species

If humanoids could evolve in the liquid, then different other kinds of species may evolve in the same liquid. All different species could contaminate the liquid.

Answer 4

No

The combination of having a human-like species and a communal blood supply are incompatible. The blood a person uses has too many "personalised" components to allow for a one-size-fits-all supply. Nutrients need to be tailored to individual energy and growth requirements that vary radically over time. The nutrient composition of the blood of a new-born baby, a toddler, a youth just hitting puberty and a mature adult will be very different. Even within those groups, the nutrients required by an athlete and an office worker will be very different. You may posit a very enriched nutrient content for everyone and bodies with each individual cell being sufficiently "smart" to only take the nutrients it requires, but a creature like that is not remotely human.

Secondly, a humanoid body pattern does not make sense for a species that need to spend most of their time floating in their blood-like substance. The human body plan is optimised for walking and running long distances, climbing when required, spotting threats and opportunities at a wide range of distances, throwing objects accurately and general tool use. The tool use is the only useful ability for a species living in a (probably opaque) liquid that they can only leave for as long as they can hold their breath. The arms might work, but the legs can definitely be traded in to get a useful tail and the head will need to change considerably to facilitate sonar. (How to generate sounds for communications and sonar in the absence of lungs is left undefined.)

Note 1 - all of these problems disappear if the species simply has single-user devices providing the blood supply. The question is why build all these functions into an external device when the lungs, stomach, intestines and other organs could handle these functions internally.

Note 2 - I have deliberately omitted any discussion of waste removal, filtering and cross-contamination. All the air-breathing animals on Earth breathe a communal atmosphere that we are each expelling waste products, bacteria and viruses into constantly. Similarly, aquatic animals are expelling waste products into communal water including fecal matter. Given this situation, these are clearly solvable (or at least species-survivable) problems even without high technology. A separate excretory system to handle waste without contaminating the "blood" supply would probably be a good idea though.