Ant 128A: Fox Field Guide (3)
Ch. 1. Diagram 9; p. 47. Cognatic descent
In this case both brothers and sisters bring in spouses and have children who are counted as members of their descent group. This is shown most directly in Diagram 8, not duplicated in this handout. It means that descent is reckoned through both male and female links. This descent system thus is not unilineal. It has the disadvantage that individuals (represented in my drawing by the overlapping, shaded and unshaded triangles or circles) belong to at least two groups -- their father's group (shaded) and their mother's group (unshaded).
This is a cognatic system because it ignores sex in tracing kinship links.