And your evidence for that is?
Seems to me humans get along just fine even with non-sapient animals (i.e., cats, dogs, etc.). Sure, we compete with other species, but evolution isn't just about violent competition: there's also other means of competing (reproductive fitness, for one) as well as plenty of examples of cooperation (i.e., symbiosis).
I'd rather not go too far along this topic, because it's a distraction from the main thread, but that seems like a pretty closed-minded view to take, since we've never actually had experience dealing with other races or species we could communicate with before. In any case, elves, dwarves, and the like are closer to sub-species than non-human.
I agree with this as well. We should see cultural variation within any races presented, at least insofar as human show variation within the game (presumably most human settlements will share a great many cultural similarities given the likely scope of the game, but there's likely to still be variation).