Nobody quite knows where Humans originated from, or how they came to be spread across a million worlds..
Biology and Appearance
Although there are many planets in the galaxy which are generally populated only by humanoids, such as the Corellians and the Alderaanians, there are no biological differences between them. In general appearance, humans are bipedal and have two arms ending in hands with five fingers on each. Human skin tones range from nearly white, through shades of tan and brown, to nearly black. Human hair can range from a complete lack of hair through any shade and any style.
Society and Culture
Humans have always played a prominent part in the development of the galaxy and in galactic politics, not least because of the Empire's hatred of non-human races. They can be found anywhere, engaged in many different pursuits: Mercenaries, pilots, smugglers, merchants, Imperial recruits, assassins, farmers, crime lords, labourers and many others.
Humans are also naturally attuned to the Force, turning out more Force sensitive and Force users than any other species, with the possible exception of the Gand. Many famous Jedi, both of the Old Republic and under the Empire and the Alliance, were Human.