Actually, if you bother to look you'll find that tribal societies often have very rich culture and rules around marriage exactly because "worrying about inheritance" is a critical for their very survival. And "worrying about inheritance" is also a substantial part of the reason there is a rich history of marriage that goes beyond one man marrying one woman in these societies.

E.g. many African tribes have traditions for polygamy that are either explicitly intended to deal with men being likely to die earlier (as fighters or hunters) to safeguard the viability of the house-hold and/or to deal with inheritance in societies where women were often not allowed to inherit (a typical case being a social obligation in some tribes for a man to marry his deceased brothers wives in order to ensure she still has somewhere to live).