I am thinking of adding the Eberron Shifters to Golarion, but I can't think of a history for them. Has anyone done this, and if so how does society treat them in your game?
Option 1: Tribe of Kellids, or maybe an old sect of Kellid shamans/druids that through secret rituals infused themselves with animal spirits and created a new part-man, part-beast hybrid race.
Option 2: As above but it were Mwangi witch-doctors and shamans that were responsible.
Option 3: Shifters could be result of Runelord of Transmutation (bleh, PF wiki lists Runelords by favored sin but not their school, and I don't remember which is which) experiments on Varisian/Kellid people and lycanthropy. Or maybe Nex could be resposible. Or Tar-Baphon.
Option 4: Shifters could be result of partial lycanthropy amongst Varisians. Or it could be effect of failed attempt to cure lycanthropy. Or descendants of people actually cured of lycanthropy. Or descendants of mixed lycanthropic bloodlines.
Option 5: Shifters could be favored pets of gnomes that came with them from teh First World and became mortal together with their masters and the price they pay for living in mortal world is their growing bestiality/growing humanity.