Toril is home to a multitude of races that are present in numerous spheres throughout the Multiverse. Learned sages of modern Faerun maintain that many races; such as the sarrukh, batrachi, dragons, humans originate on Toril and other races such as elves, dwarves, and giants migrated here at several points in history. Scholars on other spheres such as Krynn and Oerth maintain that humans and a variety of other races originated on their own planet, logic dictates that only one can be right.
The most popular theory across the Multiverse is that all races originated in a single sphere and migrated through portals to other spheres, no one knows where this progenitor sphere is (or was). Snippets of documents signed by a being known only as the Metatext speak of how the Multiverse was originally one Universe that was fractured and each catastrophe fractures the Multiverse yet again into an infinite number of imperfect copies. Each of these copies tries to replicate the original and so humans as a race originate on Toril and Oerth and Krynn all at once as did many other races, however, beings and sometimes groups of beings also migrate between the spheres as the elves and dwarves did to Toril.
Humans are believed to be one of the native races of Toril; having long served as slaves of the sarrukh before the elves arrived and noted their primitive existence, although many subraces of human have migrated to Toril over the millennia to give rise to one of the most numerous and successful races on the planet.
Humans can be found in every corner of Toril and almost always rise to dominate wherever they are found. They are short lived when compared to most other races, possess little or no distinguishing features or abilities, and always seem to enter into conflict with any other races nearby. Many other races regard humans as little better than goblins or orcs (fast breeding pests), however, unlike the goblinoid races, humans are willing to cooperate and coexist with other races such that most have chosen to use humans at some point as a buffer against the goblinoid plague.