You might have heard or seen this one before.
I'm imagining a world where you see humans, dragons, shapeshifters, and more living on one planet in harmony. Do you really think it's possible? Can more than one sentient species can share their dominance with others?
There are pros and cons of this scenario since I am making a world with multiple species, do we have any knowledge of something similar happening in history that we could compare this to?
No, historically speaking.
So Homo Sapiens have been around for (and potentially drove to) extinctions for at least two other almost-certainly-sentient human subspecies, Denesovians and Neanderthals. Both these groups are known too have used tools, and both (though the evidence is less definitive for Denesovians) did things like bury their dead with ceremony and make clothing. Humans co-existed on the same planet as these guys for 100,000ish years. However we also seem to have been pushing both these groups (again, the proof is much better for Neaderthals than Denesovians) into smaller and smaller territories once we spread out of africa enough to encounter them. So while you can say "hey we inhabited the same planet at the same time" you can also say "we warred with our only sentient competitors from the moment we met them until we drove them to extinction." Sure there's a little Neanderthal and Denesovian DNA in humans nowadays, (a % or 2 neo in europeans, a % or 2 denesovian in asians, to paint with a VERY broad and still argued-about brush.) but that doesn't disguise the fact that we seem to have driven them to extinction. A % or two could easily be an artifact of "kill every man, child, and old woman in the clan, make the surviving women slaves" which isn't what you'd call "peaceful coexistence!"
There are a couple other species on the planet arguably sentient, elephants, dolphins, a species or two of great apes, and pigs being the most famous. We are.... not really friendly with any of those either. Of the four, pigs are enslaved foodstock, great apes and elephants are a fading fragments, and dolphins are only recently protected. You'll note that it's only the one that doesn't actively compete with us and is hard to get at (dolphins) that seems "free" from direct human abuse.
Ravens and Grey Parrots are also species that some people argue are "sentinet." I discount parrots because "the smart ones are as smart as a 4 year old" is the intelligence ratio I see bandied about for them, and that doesn't strike me as "truly sentient." Ravens use tools, talk to each other, and seem to mourn death from time to time. If we grant Ravens are sentient then they're the only such species we have anything approaching a healthy relationship with. Probably because they're able to escape us easily, aren't much of a threat, and benefit from us being around.
So what does that mean? To me, it means that a planet with multiple sentient species needs to either A: have them separated geographically for thousands of years of social development. (Columbus discovers dino-people instead of native humans) or B: The species are mutually beneficial (the Faries and humans coexist because human grain stores attract things Faries eat) or C: operate in near-totally mutually exclusive environments. (Merpeople and humans). Of these, Option B seems most likely to produce "harmony." Option A is just begging for the Other Species to take on the role of demon inferior/witch-aligned devils and xenocidal war breaking out the second they meet unless you got REAL lucky. After all, genocide is a well-warn trope for different groups of the same species meeting for the first time! Option C could result in a live-and-let-live, but just as easily devolve into warfare as one side encroaches on the other's habitat (classc fisherman-overfish merpeople land) or raid for items rare in their own environment or that are hard for them to produce (bird-people raiding human territory for metal goods.)
ADDENDUM: I should point out that this "murder the thing that's competing with me" (and all sentient beings on the same planet would, to some extent) is a common trope throughout nature. Ants war with other ants AND termites. Humming birds stab other humming bird species to death with their beaks, the various apex predators in africa all murder each other's young for sport, etc and soforth. So, "yeah HUMANS do that, but other species might" while technically possible, doesn't seem to be borne out by example in nature.
We technically already do that.
Sure the difference is a lot smaller then the one between dragons and humans, but the different "human tribes" are also forced to share their domain/resources. (Think of cultural, religious and racial differences that set us apart)
Pro's are only there when the differences are enough. Why? Because the most important aspect would be the way in thinking in terms of technology. For example an aquatic species they would develop better engineering concerning water (perhaps things like algae's as energy source). But seeing you have no information on the species that are dominant this question is one you need to answer yourself. You can do this by setting up a series of tests/problems and think about how each species would solve the problem. Some would have the same solution, while others will opt for different ones. This way you can build there culture/technology around this. Such technology can be shared/stolen to improve each other.
This would also work by just having the same species far apart, if you look at how much Asia and Europe learned from each other when they first started trade routes. The reason for this is because people often see the mission as completed when there is a solution and stop looking for different/better solutions. A culture facing the same problem without this solution might find something else.
Con's Discrimination/tension. A problem we still haven't solved (As evident in France currently) is that changes divide is and often causes a level of distrust. this could escalate to higher conflicts negatively impacting all groups involved.
Theoretically this can be solved in two ways.
If the species share the exact same domains, i.e. have identical or very similar abilities, needs and preferred climates, then war is inevitable and will eventually (possibly only over millennia of time) lead to the extinction of one of the species. Or complete enslavement of one by another, to the level of turning them into domesticated animals. As we humans did on Earth, except being the same species we only killed or assimilated cultures and territory, basically turning the enemy into ourselves rather than wiping them out. (usually)
If the species have very different domains, for example seadwelling dolphin-octopi and landwalking erect apes, then active cooperation is very likely. Or maybe they just completely ignore each other. There is no means nor motivation to fight the others.
If their domains overlap somewhat, but not completely, is where it becomes interesting. There will be some cooperation, and some competition. The oddcasional pogrom and genocide. Wars for resources, trade federations for mutual benefit.
Say one species of Avians live in the mountains in the desert, but also hunt in the grasslands. Another species of Centaurs lives in the forest but also farms the grasslands. This would lead to huge conflict between the two species, but due to their utterly different means of locomotion they would be unable to engage each other in their homelands. The Grasslands would be the site of many conflicts though. But even if, say, the Centaurs develop archery technology that can give them complete military superiority in the grasslands, they would be unable to exterminate the Avians. Quadruped Centaurs would simply have no way to attack the Avians at home, not would denying them the grasslands starve them sufficiently to kill them all.
Yes, multiple sentients on the same planet is possible, the only impediment is that they develop at more-or-less the same time, to the same sort of level.
in my opinion especially if it has human, probably human goes full genocide as the same thing to what happen to our prehistoric primate cousin if it taken place since beginning or prehistoric time even more so if they are a treat, unless this other sentient/intelligent species submit to us and dumbed down to be loyal from the selective breeding or they simply look or act cute/funny.
besides looking at human, it already hard to live harmoniously with each other especially in multiculture nation, simply because the person has slight difference either skin or different opinion or mindset etc.
it may be possible for harmony for different species, if human is out of this though, assuming this human behave like our human.
I point out that among mammals alone there are about a hundred existing species of primates, proboscideans, and cetaceans which might possibly be considered to be, like Homo sapiens, semi sentient or even fully sentient by objective outside observes.
And I believe that large brained species of proboscideans and cetaceans have existed for about ten or twenty million years. Thus it is perfectly possible that there has been a continuous condition of several species of intelligent beings sharing the planet Earth, peacefully or otherwise, for ten or twenty million years.
And it is possible that other species of intelligent beings have existed much longer ago, and sometimes shared the planet with other species of intelligent beings for long spans of time. Posssibly Chephalopod species might sometimes develope sentience.
And there is a suggestion from 2011 that about 220 million years ago a giant cephalopod arrainged the bones of ichthyosaurs in a pattern resembling tenticles in a sort of an "octopuses garden in the sea". So there may possibly have been semi sentient or fully sentient species of cephalopods for hundreds of millions of years.
https://www.npr.org/2011/10/14/141356526/seeing-a-cephalopod-in-ancient-bones[1]
So possibly Earth is an example for the peaceful or otherwise coexistance of several species of intelligent beings.
Added 11-03-2020 One series which is very optimistic about widely different intelligent beings living together mostly in peace is the Disney Company's Mickey Mouse Universe and Donald Duck Universe. The people of that setting appear to belong to humanoid versions of many different species of Earth life, and often unintelligent versions in natural size of some of those species are seen.
Whatever the actual number of separate intelligent beings in that fictional universe, the fact that most varieties of people largely resemble actual separate species of non intelligent animals would seem to give anyone racist a lot of things to sterotype other groups with.
Oooh I love this question! I read recently that some of the Great Apes are progressing into their own version of the Stone Age (http://www.bbc.com/earth/story/20150818-chimps-living-in-the-stone-age)
Add to this the fact they can communicate with us (and have for some time) (https://www.youtube.com/watch?v=FqJf1mB5PjQ), have experienced war amongst their own (https://en.wikipedia.org/wiki/Gombe_Chimpanzee_War) (sorry for the wikipedia reference but infinitely easier digest than the scientific papers associated; they are linked in the wikipedia article however so, enjoy)
I'd say we're fairly close to that happening in either case.
Other candidates for this level of sentience would be swine, dolphins and birds, amongst others: https://www.businessinsider.com.au/the-smartest-animals-in-the-world-2014-4?r=US&IR=T
