Growling came about as music got more extreme. It's just a way or making music harder. Beautiful high pitched operatic vocals are no way as extreme as gutteral growls, so for certain genres, the growling fits.
I reckon it started with Motorhead, Venom took it further and added Satanic themes, then Thrash Metal came about, still melodic growls though.... Thrash evolved into a harder sound, and thus the vocals got harder and less melodic, Possessed started it I would agree, and then the Floridian Death Metal Scene came about and all the bands adopted it.
It was just evolution really, all metal follows some sort of line and you can see where things were derived from... except for numetal I would say though, that sorta just popped up on its own...