What I'm actually considering here, because I don't want to include real-life racial modifiers in the game, is this:
Your stats are determined by upbringing and class.
For 'unique' backgrounds such as Savage Child or Homunculi you pay experience for a certain ability or pattern of talents as with the special background in Dark Heresy.
So Savage would be something like a 'homeworld' origin, a tribal upbringing and Savage Child would be more of a Tarzan-style, raised-by-animals background.
You could have Savage, Workhouse, Poverty, Mercantile, Traveller, Bourgeoisie and Gentry, just off the top of my head.