Unavailability of sex outside marriage. Pre-marital sex leads to marriage. Divorce difficult, remarriage impossible. Legitimate children are privileged relative to illegitimate. B. Males as free agents.
Households consist of mother and children.
Intense competition between men for access to sex. Most people engage in monogamy. A few powerful males are allowed to have multiple wives. Monogamy and patriarchy are connected. Patriarchal privilege is one of the glues used to bind men to marriage as an institution.