The creation legends of all demihuman races stress the bargain made by the gods of humanity and those of their own races in allocating living space within the worlds created. Out of time, when the ancient and greatest of gods created the worlds, Moradin the Soul Forger took the mountains for the dwarves; Corellon chose the forest and woodlands for the elves; Garl Glittergold took the flinty and rocky hills for the gnomes; and Yondalla took the meadows and fertile valleys for the halflings. The protean humans were allowed to live wherever they could find sustenance and reward. The gods agreed, and it was good.
The coming of strife to the world is almost always held to have begun with the violence of Gruumsh, the orcish god, and with fell creatures which emerged from the darkness of the Underdark and the lands below the surface. The elves spea of the driving of evil ones from their midst into those dark subterranean realms (the origins of the Drow) and the dwarves likewise tell tales of a similar banishment of brethren turned to evil (the duergar and derro). These two races admit the growth of corruption within the hearts of foolish and over-proud members of their own races, and a consequent driving-down of banished offenders into a deep darkness (both spiritually and literally). But gnomes, for example, have a different set of myths relating to the underworld, for they feel a strong kindred spirit with their deep-gnome bretheren, the svirfnebli. They hold Callarduran Smoothhands, the god of svirfnebli, to be a benign explorer of the deeper lands below the surface world, a light-bringer rather than an evil repressed.
So, while the racial creation myths are similar from world to world and from race to race, the demi-humans certainly have their own tales and histories to tell.