Most Humans are natives of Innworld. Some Humans have been summoned from Earth: It is not known if the so called Earthworlders are somehow different from Innworlders, although there are no indications towards that.
They are the overwhelmingly dominant race of Terandria and Northern Izril, where only white Humans live (those who would be called "Caucasian" on Earth). As the majority, Humans put considerable pressure on the Half-Elven and Dwarven minorities.
Their race is also dominant in Chandrar, where they compete with String People and in some places Garudas. On this southern Continent, "darker" skin colors have been reported with Humans, although it has not been confirmed how bronzed or dark their skin tones may get.
The only places where Humans are rather uncommon, are southern Izril and the House of Minos.
Humans of Innworld have a tendency to form Nobility to rule their kind. Terandria, Rhir and Chandrar are well-known for their Human Kingdoms; while Baleros and Southern Izril don't have such.
Humans have a reputation among other races to have stronger criminal tendencies. Especially among Drakes and Gnolls they are easily associated with common theft, which may stem from the cultural memory of the Humans stealing Northern Izril from them.
Predominantly Human cities have less effective [Guards] than Drake cities. Apprehending criminals of higher levels is a job given to Adventurers instead of City Watches which are generally of lower level and not seeking out conflict.
It is well-known among most races, that Humans are not always averse to breeding with other races, which is facilitated by fertility magic and potions. The result of those dalliances may result in Half-Trolls or Half-Giants, but also in Humans that have Scales (interbreeding with Lizardfolk or Drakes). Given that all other races also enjoy inter-species marriages and mixed children, the tendency of Humans to "mate with everything" may be overstated, especially since some Humans don't entertain the thought of having sex with other species.
So far, the exact relation of Centaurs, Fraerlings, Minotaurs and Beastkin to the Human race have not been revealed. Given that all these races share humanoid attributes, they may originate from magically altered Humans.
Conversely, all known [Nobles] of Terandria participate in a breeding program that results in bright (e.g. red, green, blue and blonde) hair colors, which is how pureblood Humans are easy to recognize.