I've got a planet similar to Earth, with three species rising from prehistoric nomadic life to sedentary civilizations at the same time and learning speed, but in three different living environments:

  • One is similar to humans, living on the ground, outside, and colonizing continents surface.
  • Another is living underwater, on shallow waters of seas and oceans, so mainly on continent coasts. It will extend to deeper waters as its technology evolve.
  • The last one is digging caves and tunnels in order to live underground, under continents surface. As time will pass, their population and technology would evolve too, and they will be able to dig deeper and deeper, eventually under the deepest abyss at some point.

They all omnivorous creatures, and have enough food on their respective living environment, and anyway would get few - but still a little bit of - food from another living environment. Their environment fit quite good for their respective natural liver, but they wouldn't be able to live in another. (As humans wouldn't have any reason to prefer to live underwater rather than on ground) So they basically don't have any good reason to colonize another living environment.
They have all the same aggressiveness and imperialism level: the one of human kind.

My question is: as none of them is a direct threat for the others, at least not for territory quest, what their relations would be ? Would one of their kind seek more wars with themselves or with one of the two other civilization ?

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    $\begingroup$ Just checking... each is a distinct species with no cross-breeding potential and each one can gather or harvest enough food crops from their environment to feed their growing populations. Right? $\endgroup$ Aug 19, 2016 at 12:51
  • $\begingroup$ You may find some of the answers to my recent question How can humans coexist with an intelligent carnivorous species? useful, even though the scenario in your question is different. $\endgroup$
    – user
    Aug 19, 2016 at 12:52
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    $\begingroup$ A few more questions... Are all three species omnivorous? carnivorous? How hospitable is each of their chosen environments? Are they each the apex predator of their environment or are the creatures which eat them? What does each have that the others might need? $\endgroup$ Aug 19, 2016 at 13:01
  • $\begingroup$ "what their relations would be ?" it is all up to you. Making one of them threatful or not, peaceful or not, more imperialist, aggressive ... Is up to you. Find in my answer potential reasons for both war and cooperation. $\endgroup$ Aug 19, 2016 at 13:10
  • $\begingroup$ @HenryTaylor I added - late, I agree - details that you asked. $\endgroup$
    – Aracthor
    Aug 19, 2016 at 14:10

6 Answers 6


About war potential

Your digging population will, sooner or later, disturb the land one. Digging everywhere to extend their civilization will probably raise landshifts and land modifications at the surface. Some buildings could crumble because they dig near the surface or something.

The sea civilization will maybe be disturbed by the land civilization. If they extend on continents, they will probably have some fishing areas, where there will be contacts with sea people. You only knows if this is possible.

Finally, nothing stops sea people from digging, too, for their structure and foundations, in which case they may fall in digging people's roads, dug just right under their nose or something.

About relation potential

Land people maybe will need some materials found deep underground. Digging people will have to breathe, so they will need some kind of air supply from the surface. Sea people won't be able to build anything without materials, and the best materials should be found either underground, or on the land.

You have a lot of commercial potential there. Selling minerals between Dig and Land, or exchanging it for air entry from the land. Sea people could trade their fishes and food against materials to build their construction, or utilities. Digging people could be interested in a water provider, in the name of Sea people. They may give others what they have compared to them, and make some useful trades-off to be able to survive.

Once again, you're the one deciding whether sea people need materials, digging people need air or land people need fish. Those are just potential interactions between them, as asked.


About your edit, you shall specify something: are they curious ? If they have the same level of imperialism and aggressiveness, they shall, after a while, be curious about what does the others could do for them. Humans have a slight tendency to think about itself and taking everything in reach without really thinking about what it takes.

Sea people could maybe realize that they have the upper hand on digging dwellers, and may try to flood them in order to gain territory underground. Flooded tunnels may be a nice extend.

Land dwellers could be curious and try to see what's underground, or construct devices to probe in seas. They would later realize that sea people are way better fishers that land people, so they would try to make them fish for them, returning pretty much nothing.

Digging people may take air entries by force, because they can basically destroy any land building with ease. By polluting waters, they could also threaten the sea people

Be careful about human behavior, really. If one of your three species realize that it can take the upper hand on the others in order to improve their lifestyle or technological advance, they will obviously do it. That's how humans work.


Those are only hypothesis. Once again, you're the only one deciding which one of the paths (hyper aggressive, aggressive, passive, neutral curious, "good-way" curious) each one of your species take.

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    $\begingroup$ "You only knows" I see what you did there $\endgroup$
    – Tin Wizard
    Aug 19, 2016 at 18:08

Drinking water will probably be their first encroachment into each other's welfare.

If the ground-dwellers casually pollute an underground river while fertilizing their crops, the under-dwellers may take offense. Then when that contaminated water reaches the coast, the ocean-dwellers might also face challenges. Especially if their spawning grounds have to be in shallow waters near fresh water river openings.

From an alternative direction, the mole people might accidentally destroy an artesian well or drain a lake during their tunneling. They might also loosen salt and mineral deposits into underground rivers, poisoning them for downstream and outlet to ocean usage.

The ocean dwellers have the most opportunity for isolation, but they will be held accountable for all that comes from their ocean domain. If a hurricane demolishes a land-dweller village or a tsunami floods an under-dweller complex, the survivors will may blame it on magic, cast by the mighty mer-folk.

Each species is probably more likely to encroach on the welfare and autonomy of other groups of their own kind, than they are to cause damage across species lines. The opportunity for conflict is higher among peoples of similar wants and needs. But the potential for inter-species ware still out there waiting, and as our neanderthal forebears sadly discovered, such wars are horrible things.

Historically, all that we have ever needed as cause to wage war, was a little bit of difference; a method of differentiating "us" from "them". These three species will have a wellspring of difference to draw on. So eventually... inevitably... there will be war.


This is a really difficult question to answer with only the information provided. Removing the competition for living space and resources means that wars would be fought for reasons such as religion, politics etc. If one of the groups suddenly develops a religion that states that all other intelligent life was created by an evil god and must be destroyed? That might end badly. Same if the mole people accidentally cause a surface city to collapse into a hole.

Because of the difficulty in even fighting a war when they live in a completely different environment (how is a land based soldier going to fight in the ocean? or a fish on land?) It's pretty safe to assume that there wouldn't be much of a threat to eachother until tech increased to the point where such fights could happen, even trade will be awkward before a point.

Then we run into the cold war. Once tech reaches a certain point and everyone has weapons that scare the others the relations will become tense, especially since relations prior would have been infrequent due to the different environments making tourism infrequent. Either the tension comes to an end and everyone reaches a truce or bad things happen.

My thoughts are that before tech improves to a point where they can do anything to eachother there won't be any problems but the barriers to understanding eachother means that when that point is hit? Sudden tensions and possible global war.



Lets look at some of the basic setups here:

Sea Dwellers and Land Dwellers

Chances are, the sea dwellers will spread out on the coast.

Surface dwellers like coastal land, because it is some of the best land.

So they will be in close contact. They will have some overlap of interests (which can be a source of competition or cooperation).

Sea Dwellers and Underground Dwellers

Underground dwellers won't really have any major relations with sea-dwellers. They can't dig too close to the sea anyway and there is little overlap in interest.

Land Dwellers and Underground Dwellers

Land dwellers can probably make tunnels (even if there isn't much food for them down there), and underground dwellers can probably live on the surface (even if there isn't much food for them up there). Indeed, to some extent it is probably necessary for either of these races to do just tthat if they were alone (for example humans often need tunnels to mine). But underground dwellers are a lot better at tunnels than land-dwellers are, and land-dwellers are a lot better at completing tasks on the surface. So, there is a possibility for them to help each other out a fair amount. However, note that surface dwellers rarely need to mine deeply, and underground dwellers probably rarely need to complete any task on the surface. So while they can definitely help each other, they also definitely don't need each other.


Beyond this point... Assuming all of these races are a bit like humans... It's pretty much all up to politics.

I could envision coastal city-states rising up that include sea-dwellers and coastal surface-dwellers under one banner, fishing, farming, and trading well. I suspect that such a society would be uncommonly prosperous, and it's a lot harder to hold deep resentments when everything is going well. This means that the two species, at least in the locality of such a city-state, would be coexisting successfully.

I could also envision a large land-dwelling nation with some of their boarder on the coast being seriously annoyed that this stretch is largely claimed by sea-dwellers, and building warships and harpoons so that they can use their coast normally. In this case the warships would probably get sunk and the large centralized land nation would keep being annoyed. Full scale conflict would be difficult, because either A) they don't have sufficient technology to stand a chance in the enemy's home turf or B) they have enough technology that they reach the mutually assured destruction problem, and full scale conflict is still impossible.

It is possible that underground-dwellers trade minerals and similar raw materials for crops and wood on the surface. This could happen on the fringes of a large land-nation, or they could be members of the large nation who tend to specialize in things like mining, or they could be completely foreign but occasionally trading (the last one assumes that these underground dwellers more or less don't need any food from the surface, which you hinted is true).

It is also possible that the underground dwellers keep their distance from the land dwellers, and any land dweller who goes into their cave doesn't come out because they don't like visitors. In this case I really don't see full war being common though. Too inconvenient. Unless some event happened that really, really enraged on or both groups, they would pretty much just trade or keep their distance.

In Summary

In summary there are two basic types of relationships species like this are likely to exhibit. Other types of relationship are possible, but they are probably unlikely without some kind of major catalyzing event.

1) A single nation comprised of both of the two species, where both of them belong in society, and the society enjoys some measure of prosperity because members of society are biologically more able to specialize. In such a society, racial tensions are still a very real possibility, but open war between species is impossible because they are all part of one nation (I suppose a civil war can't be ruled out, however, this would only be remotely possible if the two species occupied different geographical areas within the single nation. For a civil war to break out, the opposing sides can't be evenly distributed across the entire nation; there needs to be localities that all support one of the two sides. In my city-state example, civil war is quite unlikely because everyone lives in one city or the surrounding area. I don't recall any time in history where a city state underwent civil war. City-states are prone to competition with each other, but they are too small to sustain an internal, sectionalized conflict.)

2) Two separate nations, one of each species, that remain mostly aloof. Sporadic trade deals and border skirmishes will happen, but neither trade nor border skirmishes are terribly useful to either side so they mostly keep to themselves and expect the other nation to do the same. This option isn't very exciting, but it is a very real possibility.

Chances are, in an entire planet there are some nations or pairs of nations that exhibit the first behavior, and some that exhibit the second. At a given point in time, both possibilities are expressed somewhere.


war between species would be nearly impossible. each species would completely dominate any battle fought in their domain. as such, wars simply wouldn't happen. there might be some skirmishes on the borders, but there is no way that one species could ever conquer another, so full-fledged war is out of the question. however, trade is quite likely. the merfolk would trade fish, the morlocks would trade metals and gems. the surface folk would trade crops and leather. as modern technology appeared, there might be the possibility of warfare since you could poison the entire sea, or cause continuous earthquakes. even then, it seems unlikely that you would gain much from committing genocide.

side note: it is not clear how the morlocks would survive. nearly all life on earth depends on energy from the sun. assuming the morlocks use some sort of radioactive material for energy (therefore food), that could be another item of trade (or combat).

  • $\begingroup$ Yes, I too was wondering about the viability of the underground race, especially if we are to assume that they don't heavily rely on surface resources. I was thinking they might use geothermal heat as their energy source, although radioactivity isn't impossible either, assuming the planet has much more radioactive material than earth does. Also I agree with the assessment that full-scale war is impossible in this case. Technology would enable war to some extent, but assuming each species' technology roughly matches that of the others, war would still be very difficult and impractical. $\endgroup$ Aug 19, 2016 at 19:16
  • $\begingroup$ technically geothermal energy is caused in large part by radioactivity. moreover, radioactive material can be concentrated into a density capable of sustaining life. i think the idea of thorium flower farmers much more compelling than a pre-industrial society somehow harnessing a temperature gradient over several vertical kilometers. $\endgroup$ Aug 19, 2016 at 20:05
  • $\begingroup$ Hm... Perhaps so. If they are pre-industrial, either source would be difficult. But radioactive materials (ideally the kinds that give off mostly alpha radiation) are probably a more attractive source of energy in either case, provided they are sufficiently plentiful. $\endgroup$ Aug 21, 2016 at 1:53

The three civilizations will inevitably clash over resources and the territories where they are found: your continentals will want to fish the waters where the aquatics live; they'll want to dig up metals and aggregate where the subterraneans live; the subterraneans will eventually discover photosynthesis makes for better food and will want farm land; they will also want to secure sources of fresh water; the aquatics will also need to dig for minerals. The aquatics will be on the receiving end of continental and subterranean water pollution too.

Some of this could be mitigated by trade, however. Continentals and aquatics may trade food, continentals and subterraneans could exchange metals/minerals for farm land or fresh water, etc.


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