This is my first post on here, I've looked over all the tour and the help center things, so I hope this is formatted correctly.I've been working on a high fantasy world that includes a lot of the standard fare (orcs, elves, etc), but I've been reworking their biology as I really enjoy speculative biology.

The problem I've been running into specifically regards my orcs, who I've reworked to be a golem-like people with skin of dense layers of rock and softer stones within to create something somewhat analogous to the human muscular system. Two important aspects of them is that their only present sexual dimorphism is that one of the sexes grow radioactive minerals on their skin and that they primarily live within cliff faces / partially underground.

What I'm currently trying to solve is how they would generate energy to move in a way that is analogous to humans- similar to eating / breaking down food for energy. Or alternatively, like plants, like consuming something to get energy. Especially something that would be cost effective and sensical, as it would likely consume more energy to move a body so heavy.

Personally, I'd prefer to not hand wave it away with unexplained magic, and I'd like them to not have to eat standard food. Below are the options I was considering, but I'm open to more concepts:

  • Consumption / internal chemical reactions of radioactive material.
  • Geothermal-like reactions (Give them an internal structure like the inside of the earth. I feel this may make them dangerous to be around other more flammable species.)
  • Solar energy

In theory, what would be the best, most cost-effective source of energy for these guys?

  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Apr 17 at 16:37
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    $\begingroup$ This is a pretty exhaustive list $\endgroup$
    – M S
    Commented Apr 17 at 19:10
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    $\begingroup$ Magic can have constraints, sources, and a need for a regularly repeated resource-consuming maintenance activity. There's no need for a dilemma between "I want biologically plausible room temperature rock people" and "IDK magic lol". Consider vampires: corpses animated by demonic magic, they need fresh human blood (resource) which they drink (maintenance activity) to replenish the false life of the corpse (source). If deprived of blood for a long time they wither, weaken, and fall into a deep comatose state (constraint). $\endgroup$
    – g s
    Commented Apr 17 at 19:17
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    $\begingroup$ As worded, any source of energy is an equally viable solution: chemical, nuclear, solar, the souls of thier enemies, etc. would all make equally useful answers. Please update this question to let us know what criteria a best possible answer would have to meet. $\endgroup$
    – Nosajimiki
    Commented Apr 17 at 20:20

1 Answer 1


Humanoids use far too much energy in movement to be able to physically get that energy from their surface area through solar radiation. More than half of our skin is in shadow at any one time, and our surfaces are smooth to reduce drag and narrow to get mechanical advantage with muscles. We just are not shaped to maximize how much of us faces the sun, we are shaped for efficient movement. Likewise, geothermal only works because the interior of the Earth still has trapped heat from its formation. A humanoid sized creature wouldn't be able to hold anywhere near enough heat from its formation to last its lifetime, especially since its size means it would lose it at a much faster rate than the ground does. For a humanoid species you're pretty much stuck with the chemical approach.

Thankfully much thought has gone into this angle. The classic approach to something like is to say your creatures are silicon-based lifeforms as opposed to carbon-based ones. A lifeform whose chemistry is based on silicon could in theory easily have silicates and other minerals form its exoskeleton. A carbon-based lifeform could just as easily do that (look at diatoms with their quartz and glass shells), but if you are wanting more speculative biology, silicon is a classic.

If we do indeed want to go with that approach, then the most obvious way to chemically produce energy will almost surely be the oxidation of silicon and silicon oxides to silicon dioxide: sand. While we breath in O2 and oxidize complex carbohydrates into H2O and CO2, they could eat pure silicon or other silicates and "breath out" sand. Realistically it would be the case that they wouldn't need to breath at all, and merely excrete sand as a byproduct. They could also crystallize some of that silicon dioxide to create quartz exoskeletons.

Instead of hydrocarbons like fat to store energy in their bodies, they would hydrosilicates, i.e. silicone. So just under their rocky outer skin, they could be quite rubbery and bouncy (not too much unlike our own fat deposits really).

The problem of what they eat really then comes down to you needed something to complete their metabolic cycle. Any humanoid also needs to rely on a large amount of primary producers to ultimately be the source of energy, so your world could probably include "rock plants" which do use photosynthesis to produce pure silicon and silicon oxides which they integrate into their bodies.

  • $\begingroup$ Thank you so much! I really appreciate the concepts and I'll do more research in that direction c: $\endgroup$
    – riznow
    Commented Apr 18 at 0:21

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