In the study of kinship the lineage was quickly discovered to be a social group with great organizational potential. Through belonging to a lineage, one might gain access to property, land, offices etc. A lineage is a group of people descended in direct line from a common ancestor or ancestress. In patrilinearly organized societies inheritance is transfered from father to son; in matrilinear systems inheritance is transfered from mother's brother, via mother, to sister's son. Bilateral systems (also called cognatic - not to be confused with cognitive) permit inheritance along both the mother's and the father's line. There is wide agreement that none of these types exists in pure form in any sociaty; all real societies are mixed forms. "Segmentary lineages" are a special type, in which close kin in principle always unite in alliances against more distant kin. Non-members of the group are considered non-kin, and therefore the entire group automatically allies itself against them. Segmentary lineages received such a lot of attention, e.g. because they provided extensive possibilities for understanding how egalitarian societies without kings or other formal powerholders could still organize themselves very effectively.