Question: Are there are any serious biological or evolutionary plausibility issues with separating the energy storage/production function from the production of structural/regulatory biomass?

Background: In terrestrial life biomass is initially produced by plants which produce carbohydrates and related molecules (like lipids) from photsythesis. The carbs (and related sugars, lipids etc) fulfil structural and energetic functions.

My alien life on the other hand takes the same carb-based approach for biomass which is not related to energetics, but uses alternative molecule species for energy storage/generation.

Why? My alien lives on a planet with 70% H2 atmosphere on a super earth large enough to have retained such an atmosphere. My plants generate standard carb based biomass using photosynthesis which imports methane and sunlight and exports hydrogen. See my previous question here for details. Creation of this biomass is very efficient (4-5x) in the H2 atmosphere compared to terrestrial photosynthesis for reasons I won't go into here (but see the link if interested) but the downside is that 'burning' this biomass in the H2 atmosphere produces 4-5x less than oxidising it in an O2 based atmosphere.


So my alien animals don't use carbs for energy, they use an alternative molecular species (which for now I'll call a 'pharb') which unlike carbs, produce a good amount of energy when reduced with hydrogen (e.g. the reverse of oxidation).

The 'pharb' is still carbon-based. We are not talking about non carbon metabolism here.


I have two classes of plants:

  • primary plants which are the least complex type of autotrophic life which use carbs for energy storage/generation. They grow prolifically.
  • secondary plants (call them 'phlants') which either unilaterally or in symbiosis with something else( e.g. fungi) can produce the more energy rich (in the reducing H2 atmosphere) pharbs. These secondary phlants are not all pharb, they use carbs for structure since this is efficient. Parts of their anatomy may be where the pharbs are stored (think of pharb based fruits, nuts, saps etc). Phlant biomass is approx 10 times rarer, or more, than plant based biomass.
  • primary heterotrophs (animals) which feed on the primary plants. These must be very simple creatures with slow metabolisms since they have access to only 20% of the energy terrestrial oxidising life has access to.
  • secondary heterotrophs (phanimals) which feed on the secondary 'phlants'. Thanks to their diet being pharb based, they have access to similar energy as terrestrial animals. They can digest primary plant carb based biomass, but cannot use this biomass for access to energy. The structural elements of their bodies are carb based but the muscle and energy storage/generation pathways are pharb based. Phanimal biomass is approx 100 times rarer than animal biomass.
  • my sapient aliens are phanimals.

Other details:

Surface gravity and temperatures are earth-like. Surface area is much higher because its a super earth.

Insolation levels at wavelengths suitable for the described photosynthesis process are earth-like.

There is plenty of open water, seas etc. All my lifeforms need water same as terrestrial life.

The methane which is required as the primary input into the primary plant photosynthesis cycle (analogous to CO2 on earth) is regenerated reliably within the ecosphere.

All in all, its a great place for life; as long as the heterotroph energy source problem is solved by use of pharbs.

Question restatement:

  • Assuming such 'pharb' molecules exist*, are there any scientific problems with constructing a rich setting for a sapient civilisation at tech levels similar to 1000-2000AD on this plant?

  • What are the most obvious differences with the earths ecosystem going to be?

  • $\begingroup$ I am not enterely sure of what are you asking, but animals in Earth work with an "energy producing cycle" (en.wikipedia.org/wiki/Citric_acid_cycle) that produces ATP out of ADP, phosphor and energy. When energy is needed by other cellular functions, it is extracted out of the ATP to ADP breakup. So you could say that they are two separated (to some extent) processes. $\endgroup$
    – SJuan76
    Commented Oct 4, 2015 at 23:19
  • $\begingroup$ This question is well out of my ballpark. But I will say that evolution seems to have assembled humanity as a collection of whatever was available that didn't react violently with water - and even then there are exceptions for small quantities of sodium and magnesium. We are bags of water suspended on a mineral frame with bits of things not unlike plants growing from our scalps and fingers, powered by simple critters in the lower gut that make big food into little food. The sheer impossibility of it seems to say 'just don't violate thermodynamics'. $\endgroup$
    – user8827
    Commented Oct 5, 2015 at 8:01
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    $\begingroup$ Don't snails do what you are referring to here? They manufacture shells out of (mostly) calcium carbonate, something which they cannot use an an energy source. Also although cellulose can be broken down and eaten by bacteria and fungi, the wood in the trunk of a tree is not available to that tree itself as an emergency energy store. In fact, typically a mature tree becomes cylindrical. Fungi eat the core, while the outside of the tree continues to thrive. $\endgroup$
    – nigel222
    Commented Oct 5, 2015 at 10:52
  • $\begingroup$ @sean, I agree - but I was hoping for some elucidation how people might see this two tier system developing over the longer run. $\endgroup$
    – rumguff
    Commented Oct 5, 2015 at 20:23
  • $\begingroup$ @Sjuan, terrestrial metabolism uses carbs for all of: structure, energy storage/production, metabolic signalling. A system that employs significantly different biochemistry for these functions ought to feel substantively different to earths but I'm not sure exactly how. $\endgroup$
    – rumguff
    Commented Oct 5, 2015 at 20:25

4 Answers 4


All the phanimals will be highly flammable.

One of the great things about oxygen is that a molecule of O2 effectively has a lot of energy that air breathers can use. It really likes to oxidize things, and as such, we can carry around a supply of relatively low energy oxidizable molecules and count on the atmosphere to supply us with a decent chunk of our needed energy, safely tucked in double–bonded diatomic molecules that don't burst in flames at tropospheric temperatures.

A bond between hydrogen and carbon in, for example, CH4 is much weaker than the bond between, for example, oxygen and hydrogen in H2O.
Oxygen likes oxidizing things. The only element which could oxidize oxygen would be fluorine, but it only forms one bond in most conditions. Your phanimals, therefore, are unlikely to get a lot of their energy from the atmosphere. Luckily, they don't have to.

If you phanimals are high metabolism creatures, all they need to do to make sure they have enough energy is to carry around molecules with lots of energy waiting to be released. Unfortunately, such molecules also enjoy rleasing their energy with little or no provocation. A phanimal, for example, could rely on internal stores of hydrazine, N2H4. Hydrazine has plenty of energy on its own, and doesn't even need to react with atmospheric hydrogen to release energy. Unfortunately, it can easily chain–react with itself, and burns incredibly hot. An animal with internal hydrazine stores could ignite and rapidly combust if it were struck by sparks or heated up too much. Most high energy molecules will be similarly risky, but may offer enough energy compared to hydrogen oxidizing fuels to be worthwhile for animals to produce.

Animals will live fast and die young.

Given the high odds of spontaneous self-immolation, evolution will put a premium on reproducing early. Phanimals will grow quickly, eat a ton, and start reproducing as fast as possible. Evolution will be a tradeoff between being slow and being flammable. Given relatively easy access to food in the form of slower animals and hugely abundant plant life, the need to eat a lot won't be too much of an issue for the phanimals. They also won't need to breathe, which will simplify their internal anatomy somewhat and make the transition between sea dwelling and land dwelling creatures simpler.

How will this affect civilization?

With a highly flammible portion of the biosphere which really doesn't threaten to ignite the rest, given the lack of free oxygen, your creatures will likely develop and harness fire faster than early humans did. Fire will also be much more dangerous, both to the fire-users and to potential enemies. It will quickly be weaponized, and will be far more dangerous than any other simple weapons, such as swords. Bows with flaming arrows, followed by progressively longer ranged fire-shooting weapons, will be a common weapon. Creatures will probably be fairly watery with their hydrazine stored in some form of sealed and protected internal organ, but even so, fire will be incredibly deadly to them, and these won't be standard Earth-variety flaming arrows, but rather arrows tipped with hydrazine, which will continue to burn even inside of a target, since it doesn't need oxygen to do so.

Rocketry, given the abundance of a simple monopropellant, will also develop quickly, and without any need to breathe, space exploration will be significantly simpler for your creatures, who may explore their moons before developing the most basic of computers. Getting to other planets, of course, would be a multi-generation expedition, given their life expectancy of ten years or so.

  • $\begingroup$ Thanks, great answer - especially the bit about rocketry! And some new chemistry to investigate. When you refer to developing fire are you referring to fire using free oxygen from somewhere, or alternative oxidants to react with hydrogen? $\endgroup$
    – rumguff
    Commented Oct 6, 2015 at 22:17
  • $\begingroup$ Something like hydrazine doesn't need either oxygen or hydrogen to burn, just sufficient energy. If such a compound were the energy storage medium for your phanimals, your pheople could either extract it from other animals or from their own dead. A spark from something like flint and steel would be all that would be required to start it burning. $\endgroup$
    – ckersch
    Commented Oct 7, 2015 at 2:54

Assuming such 'pharb' molecules exist*, are there any scientific problems with constructing a rich setting for a sapient civilisation at tech levels similar to 1000-2000AD on this plant?

Should be no problems. We still don't know how every link in the chain works and interrelates perfectly for our Earth, so you can assume that life will adapt in ways you cannot predict. It's always okay to assume gaps in knowledge.

What are the most obvious differences with the earths ecosystem going to be?


Your atmosphere is going to be very weird. Methane and hydrogen normally separate, but you can probably come up with weather systems that would mix them. Even then, concentrations of your primary -trophs and secondary -trophs would depend heavily on elevation; mountains would be hostile to pharbs and phanimals, but valleys and caves would be suffused with methane.

The atmosphere would be explosive anywhere oxygen would be introduced. You've got water oceans, so probably there, or wherever the oxygen came from to make those oceans in the first place. (Underground?) In particular, electrical currents could produce locations of great violence. Consider cloud-to-water lightning—yikes.

You'll want to get oxygen involved somehow, so your civilization can use fire. Unless you can find a reaction that would do the same thing for them as fire did for us. If the oceans pulled their oxygen from the earth's minerals (for example), you could try something with that.

Plants & phlants

Your plants and phlants won't remain as separate as you describe; there's huge evolutionary benefit in them cooperating, so at the very least they'd start trying to grow around or on each other.

They would more likely integrate, from normal symbiosis to as extreme as mitochondria's bacterial origins. Since they both, presumably, came from single-cell organisms, any species that interlaced with each other at that stage would have a huge evolutionary advantage.

Animals and phlanimals

EDIT: I forgot the largest question. How, exactly, are these animals going to respirate? Are they going to need more surface area than our lungs and gills currently do? If so, animals would probably need to be built around their respiration systems.

Your primary heterotrophs won't resemble animals as we know them; 20% of energy intake is a big downgrade. They would rely on external phenomena as part of their life cycle: reproduction and transportation via wind or water currents, for example. They would probably resemble parasites on your primary autotrophs.

They'd also be terrible at healing, so their defense mechanisms would focus on camouflage, poison, and other strategies that don't require moving and discourage possible predators from eating the guy next to them. I'm thinking water-borne clouds of lazy krill-like animals at best, and creeping molds for land-based. They would not be big on animal reproduction as we know it, instead preferring spores or extremely simple eggs. Maybe some barnacle-like things.

Why would your pharbs bother finding/cultivating the rare phlants when they could just eat the primary heterotrophs? 10 times rarer is worse than the 5 times less energy production. But they're so high up on the food web, you could easily justify their existence with ecosystems that turned out just right, somehow. And hey, biodiversity—where there's a niche, there's a way.

These are just guesses, but reverse-engineering a complex life web is never going to be objective or thorough—too many unknowns. Maybe you found something that tickled your imagination, though.

EDIT EDIT: I did some more quick research, and found some other things that might interest you.

At around 700 to 1100 Celsius, methane and steam react to form hydrogen and carbon monoxide. The early development of this planet probably had that happening a lot. The carbon monoxide then could react with remaining water, and so on and so forth. Where would your atmosphere's mix of chemicals stabilize at? What conditions would provoke instability? Would vinegar feature?

  • $\begingroup$ Thanks, great input. I haven't got an answer to the fire question yet, maybe I'll try and do without it, maybe not. @ckersch's answer suggests fire would be relatively accessible but I have asked him to clarify that part of his answer. $\endgroup$
    – rumguff
    Commented Oct 6, 2015 at 22:21
  • $\begingroup$ Yeah, I'm not entirely sure where his oxygen would come from. If it was too easily available, you probably wouldn't have life at all. $\endgroup$
    – Tigt
    Commented Oct 6, 2015 at 23:08

I think the idea that you will have carbohydrates and something else is a mistake.

When you mix oxygen, hydrogen, and ignition:

  • The oxygen causes the hydrogen to oxidize.
  • The hydrogen causes the oxygen to reduce.

So when your atmosphere is hydrogen based, the energy storage medium might be something that can be reduced. Perhaps something rich in carbon and oxygen, with very little hydrogen.

Having said that, it is possible your "primary" creatures won't exist at all, and your "secondary" will, and won't be too conceptually different from us.

Alternatively... it might go the way of early Earth. Some creatures might discover they could eliminate the competition by dumping poison (oxygen gas) into the atmosphere.


I'd think a compound with lots of oxygen (and carbon if carbon based life) that releases energy when it is hydrogenated is best for reducing atmospheres. something like:

$6CH4 + 6CO2 + photons--> C12O12 + 12H2$

this would work? I chose this because it can be reduced to methane and carbon dioxide gas easily with hydrogen gas. it helps renew methane in the atmosphere as well. I couldnt figure out the enthalpy of the reaction as i couldnt find the enthalpy of formation of c12o12 anywhere ;( so a quick guess is that it is very energy intensive as it tries to liberate o2 from carbon dioxide (which scientists are pewing lasers at, for starters) . you'd get a lot of energy consuming plants and a lot of heterotrophs that can easily yield energy by reducing c12o12 by hydrogen.

Edit: the total energy yieled (and consumed) by this is about 2019 kj/mole, compare this to the energy used by plants: which is about 2801 kj/mole. So this can be utilised, i'd say

This "pharb" would be the storage of the natives on the planet: analogous to glucose on here, except energy is gained through hydrogenation (plenty of which, presumably, is available in the atmosphere). It can also be used to circulate methane and carbon dioxide back into the atmosphere: and replenishing it.

I dont know if they can catenate with themselves, most likely yes (because of the high amount of carbon in them). If yes, then it can function as a structural and as a storage materialThe alt carb looks like this

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    $\begingroup$ Whilst you may be correct, it's difficult to judge because of a lack of detail in the answer. If you are able to edit to supply more, that may avoid the deletion of this answer as low quality. (From review). $\endgroup$ Commented May 4, 2021 at 11:20
  • $\begingroup$ @L.Dutch-ReinstateMonica like a little monster $\endgroup$ Commented May 4, 2021 at 12:12

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