I am considering specifically multiple intelligent species that all evolved on the same planet, and whether it is plausible that they will end up in a multi-species society or whether one species will conquer and exterminate all others.

Let intelligence describe the conjunction of these traits:

  1. Tool use
  2. Transfer of information among individual and across generations, allowing the accumulation of knowledge
  3. For the sake of argument, presumable self-awareness

I worry that the coexistence of multiple intelligent species is impossible because of these reasons:

  1. Ancient Homo Sapiens exterminated all other intelligent hominids, suggesting that xenophobia and xenocide amongst intelligent animals is plausible. (Though the extent of intelligence of these other hominids are questionable)
  2. According to the competitive exclusion principle, multiple species competing in the same niche will be eventually culled to one single species. It might be the case that all intelligent species effectively occupy the same, though likely broad niche.
  3. The numerous intelligent species, if developing separately, probably will not do so at the same rate, so that one will be more technologically advance than another when two encounters. An analogue of the American-Indian war may ensue, either exterminating the weaker species or reduce them to a status not unlike zoo animals, maybe literally.

Are there factors that may rescue the fragile coexistence of multiple intelligent species? or perhaps I mistook in my reasoning. If possible, what kind of environmental and historical coincidences may facilitate the coexistence of multiple intelligent species native to the same planet?

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    $\begingroup$ All great apes (orangutans, gorillas, chimpanzees and humans) are hominids by definition. And they are intelligent. They use tools and educate their young. There multiple species on this very Earth which exhibit intelligence. What humans have and they don't have is language, longer attention span and much better manual dexterity. $\endgroup$
    – AlexP
    Jul 1, 2017 at 19:44
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    $\begingroup$ According to your definition we are currently coexisting with a lot of other intelligent species and did this for many million years and might do this for many more. The competitive exclusion principle just says not in the same niche and does not regard free will. And: it might be not possible to proof your claim, even if we exterminate all others, only to proof the opposite when we find a society of coexisting species somewhen somewhere in the universe. $\endgroup$
    – Henning M.
    Jul 1, 2017 at 20:55
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    $\begingroup$ @AlexP No , non-human great ape are only as intelligent as toddlers. Also , Non-human ape may teach their children , but do not aggregate knowledge. $\endgroup$
    – user15036
    Jul 1, 2017 at 23:30
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    $\begingroup$ @TheoclesofSaturn A gorilla that can use sign language is significantly more intelligent than a toddler $\endgroup$
    – Aify
    Jul 2, 2017 at 3:55
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    $\begingroup$ We can barely coexist with our own species and often don't. It is presumed that we'll either eventually get the hang of doing that or kill ourselves off, but some period of conflict between intelligent cultures that are different (including different species) would seem inevitable. $\endgroup$ Jul 3, 2017 at 0:26

3 Answers 3


I have the same answer I have given for similar questions: Intelligent beings can coexist so long as they don't share the same biome.

Homo Sapiens evolved with several other hominid species (the Neanderthal and Denisovians being the two best known, but there may have been other hominid species on Earth between 300,000 and 30,000 years ago). While the exact mechanisms for our cousins becoming extinct is not clear, archeological evidence suggests that Homo Sapiens moved and worked in larger groups and over greater areas than other hominids, and would be at an advantage in terms of exploiting all available resources, and have out competed their cousins.

Species which did not share the same biome as Homo Sapiens would not face the same competitive pressures, nor would Homo Sapiens be inclined to pursue sources in very alien biomes, like the deep ocean. (This example is a bit difficult, since Homo Sapiens can effectively inhabit all land based biomes, and the Ancestors were not the kind of people who let things like mountains, glaciers or deserts get in their way).

If your intelligent species are somewhat more specialized, then they will not be in competition with other intelligent species in different biomes, and will see these beings as the magical or spirit creatures who live in the [insert biome here]. They speak, after a fashion and cam be persuaded to trade strange and wonderful things across the boundaries.

  • $\begingroup$ Good answer, but IMO incomplete. Question asks about tech progression. I'm afraid that when technology of one species progresses enough to let them inhabit different biomes something similar to colonialism (but even uglier, as hard as that is to imagine) is likely to happen. By definition of "first" one species will be the first, and advantage doesn't have to be unimaginably large to have catastrophic effect on disadvantaged species. $\endgroup$
    – M i ech
    Jul 1, 2017 at 22:56

Could easily occur, at least initially, due to differences in physiology. E.g. if you had obligate amphibian vs desert dweller. Man can survive in many climates through technology. (Igloos and sealskins are technology.) Aliens may be more restricted.

A second factor may be differences in diet. Consider a maritime carnivore (otters with hands) Their diet would restrict them to the littoral regions until they had substantial tech to support them away from the coast.

Consider a planet with more tectonic activity such that 25% of the planet was above half the atmosphere. (1/2 atm on earth is about the 18,000 foot level.) Imagine human powered combat at 18,000 feet.

At present we are working at making a substantial amount of the tropics uninhabitable by human beings. Once the wet-bulb temp exceeds 37 C, human beings can't cool themselves by sweating. Animals with higher body temps can.

A friend of mine has speculated what would happen if raccoons had opposable thumbs.

As to the inevitable extinction of a competing species, we have been unable to get rid of rats, coyotes, or raccoons, despite some earnest efforts.


I see three possibilities, where coexistence is the most rational and overall advantageous strategy; none is completely religion-, stupidity- or ambition-proof, as any of these three factors might still lead to choose an irrational, losing strategy of aggression.

Conflict is not really possible, or ruinously expensive, due to environmental incompatibilities.

For example, the two environments are mutually poisonous, or otherwise uninhabitable and unexploitable (the land and the deep sea). Imagine men and very intelligent dolphins, or giant squids.

Each might then have something to contribute that the other could not easily obtain, and this could lead in turn to a reasonably peaceful coexistence.

This is also the case with multiple races evolving on planets not in easy reach of each other, when the same technology and expense that would be necessary to exploit one race could clearly be better used to produce even more riches from uninhabited asteroids, ice moons and comets, and metal-rich planetesimals.

Conflict is possible but at no time one race was able to overwhelm the other.

If not because of environmental segregation, this would require some sort of mutually assured destruction - the two races must be at the same level and evolve at the same speed, otherwise one will become slave to the other.

One far-fetched way of getting here would be for intelligence, even sentience, not to have evolved at all in either race; it was a sort of external infection (see Dark Benediction by Walter M. Miller Jr. (1951), the parasite in The Fugitive Worlds by Bob Shaw, or the one in Larry Niven's Beowulf's Children).

It might even be the case that the intelligent races do not see each others as different races but rather different hosts for the same organism. This might (or might not) allow peaceful coexistence.

This is the case of a "hyperspace universe" where planets are in easy enough reach of each other, but interstellar conflict would likely result with greatly reduced, half-exterminated contenders at the mercy of the first comer.

One of the races is advanced and mature enough to tolerate, perhaps even actually uplift, the other.

Not too stable a situation (individual members of the elder race might still despise or hate the other race's members) but this might still happen with, say, Homo Sapiens Sapiens and chimpanzees, dolphins, orcas, and squids.


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