There's quite a bit here about orcs being related to humans, so I figured I'd throw mine in too :p

Orcs are a species of gorilla, and are typically far far hairier than in other worlds. So much so that Orc "fashion" involves the dying of patches of fur in patterns(like temporary tattoos).

As an added fun; Orcs were one of the two races to initially domesticate the rust monster. This happened during their evolution, and they used then as a kind of defence against metal-armed already-elvenoid invaders. These days, "rusties" serve a similar purpose in orc society as dogs in human society.

Additional implication; because rust monsters eat metal, orc society didn't go through a metalworking phase. Instead they manually and magically bred speciality trees (just as ironwood and dark wood) to fulfill the role for them