In Soldak games orcs are a result of a no-name Necromancer using his magic on not quite dead Elves, which transformed them into brutes that proceeded to rip him to shreds. They are tribal, not that advanced and aren't much of a problem compared to something like demons or dark elves.

By Zombasite though they "evolve" because they are hit by the namesake of the game, which is a giga nigga magical zombie virus. Dunno if any "pure" tribes remain but the virus makes them mutate into 3 main different strains: Zombielords (actually got zombified and now have the intelligence of elves, strength of a champion giga nigga magical zombie and unbound malice), dark orcs (orcs but more dangerous and ferocious) and the Mutated (which actually resemble their Elven ancestors a lot both in appearance and character but suffer/benefit from random mutations).