Even in the smallest unit of a society, a family, the most physically dominant, fearsome family member must enforce order, fairness, etc. Either a patriarch or a matriarch. As multiple families join to become a tribe, the respective family leaders arrive at a consensus as to whom the ultimate leader will be. Said leader's mandate is likely not absolute, but rather is driven by continued competence. It seems to me that as soon as that leader settles a dispute for other members of their tribe, inequality begins increasing until catastrophe returns that society to its most primitive form.