In Africa's matrilineal cultures, brothers were expected to protect their sisters and sons were expected to protect their mother's brothers as needed.
In a matrilineal society, each member is identified with their maternal lineage.
A lineage is a group of people who track descent from a common ancestor; thus, in a matrilineage, individuals are related as relatives through the female line of descent.
That is why protecting women of the tribes were so important. They played a significant role in that culture as opposed to the patriarchal society.