Bilateral forms reflect both structural and functional differences when compared to unilineal descent systems. Matrilineal and patrilineal groupings incorporate people into discrete and exclusive units. Stocks establish a system of multiple membership, since individuals belong to more than one group, minimally to both their mother's and father's, and maximally to as many groups as their have recognized ancestors in any line. Each stock to which a person belongs has a different membership composition from the others. Because people can belong to more than one stock and group memberships overlap, it is impossible to assign exclusive rights such as residence within a bilateral descent system.
Siblings 1 and 2 belong to two stocks, one through their mother's father and another through their father's mother.
They also belong to the stocks of their mother's mother (5) and father's father (6), which are not drawn in the diagram.
Stocks were present in some form in many historical European kinship systems and are especially well exemplified by the Scottish clan system. These groups originated with a named male ancestor and traced their membership through his sons and daughters, grandson and granddaughters, and subsequent descendants of both sexes. Membership in the group involved marked identities through the use of clan names and insignia, such as tartan patterns. It provided people with political support and a limited range of territorial rights. Stocks have also been described in Oceania. (See discussion of the ooi and other cognatic descent structures in the Gilbert Islands.)