Animals should be neutral, like in Beyond Divinity. Once you attack one, the whole spezies will be hostile. but when you ge too deep in for example wolf territory, the chance that they attack you will get higher. But if you befriend them lioke doing quests for them, they could become friendly and maybe even help you in combat when they are close enough. It could be like a faction system. I dont think that this would be take too long to implement that.
