Unilateral descent is a system of kinship in which descent is one can trace one’s ancestors through only one gender, either the male or the female. Based on this we can divide between the patrilineal or matrilineal line of descent. When descent is traced through the father it is called patrilineal descent. Here, the father’s family, his parents, and siblings are considered as the kin group and not the mother’s. On the other hand, when the descent is traced through the female line, it is known as matrilineal descent. There are also societies in which descent can be traced either through the father or the mother. It is called ambilineal descent.
In societies with patrilineal structure, only the males in the family take forward the family surname. Due to this, males are attributed to greater prestige and are considered the permanent members of the family. People descending by male links are known as agnates whereas they are cognates if they are the Descendents by female links. Most societies are based on the patrilineal system of kinship. However, in societies like that of the Nayars, a person traces his/her ancestors through the female line. In societies like this, there is an emphasis on unilateral descent through females, known as uterine descent. In such matrilineal societies, family ties and inheritance, all trace to women. Again, ambilineal societies are mostly present in Southeast Asian countries where parents can choose to associate their children’s kinship with the mother’s kin group or to the father’s kin group.
One important way in which unilateral principle may be used is in the formation of recognized lineage groups as a part of the social structure. A lineage group consists of all the members of a lineage alive at a given time. An agnatic lineage consists of a male ancestor, and all his descendents through males of three, four, five, or ‘n’ generation. Here, a woman belongs to her father’s lineage but her children do not.
A feature of the unilateral descent group is a corporate group which means it shapes a person’s identity, decides who he/she can marry, how property needs to be divided or distributed. It at times, also forms a political unit. It is often seen that unilateral descent group helps to define and sanction the personal field of social relations for every individual. Marriage amongst the same lineage is forbidden on the grounds that individuals are blood relatives. This system generally organizes the members of a generation into two groups; cross cousins and parallel cousins. Parallel cousins are the children of the siblings of same-sex while cross cousins are the children of siblings of the opposite sex. In many societies, it is the marriage between cross cousins which is preferred or considered ideal. Another feature is that the lineage exists in perpetuity. It never dies. It remains irrespective of births and deaths of persons. Unilateral descent also helps in the development of social relationships. It not only deals with blood relations but a social relations.