Kinship System refers to the way in which a society defines the relationships of persons interrelated by blood, marriage, or adoption. Descent is the sociological affiliation of children to their parents. A rule of descent affiliates an individual with a particular group of kin through known or presumed common ancestry. Descent rules determine group membership, inheritance of property, and succession to titles and offices. A rule of descent affiliates an individual with a particular group of kin with whom he is especially intimate, and to whom he is privileged to turn first for certain kinds of services including support and help that he cannot demand of other kin. This explains the relationship between family, lineage, descent and property. Family is the smallest descent group. Various families link together in different patterns to generate what is termed as hierarchy of descent groups. Firstly, a lineage is a kin group that consists of members who are the unilineal descendants of a common ancestor whose identity is traceable. A lineage, generally, does not include members belonging to more than five generations. Lineages cannot expand indefinitely in a single locality and often segment into smaller, more manageable and economically viable sub-lineage segments. A number of lineages combine to form clans. A clan is a kin group that consists of members who are the unilineal descendants of a common ancestor, whose identity is forgotten, and hence remains fictitious. A clan is thus a larger kin group than the lineage and includes members belonging to many generations. A Phratry is a very large kin group which consists of some linked clans, and which appears in a combination of more than two such equivalent groups in a society. When a society is divided only into two equal halves, each half is called a moiety (i.e. there is a presence of only two phtrataries). Each moiety consists of several linked clans and lineages. Such a division of society into two halves is usually known as Dual Organization. The Dani clans are grouped into larger patrimoieties, Wida and Waija that run through the whole of Dani society. Wida men are forbidden to marry women from their moiety and must take wives from Waija and visa versa. The Yanomano also have a moiety system. In their case, the participating units are small-localized lineages, which settle, in small villages along with members of a matched moiety. Marriages are usually arranged with members of the opposite moiety within the settlement.

All these groups are based on certain different principles of reckoning descent, which include particular relatives in a lineage, clan etc. For example in patrilineal system, patrilineages and patri-clans get formed including relations only on the male line. These principles are culture specific. World over these descent systems are broadly divided as Unilineal or Non-Unilineal.  

The Unilineal Descent Systems may be further classified into

Simple structures        

Comprising of Patrilineal and Matrilineal structures

Complex structures

Comprising of Double Descent Groups and Bilinear Kin Groups

The Non-Unilineal or Cognatic Descent Systems may either be

Ambilineal 

Bilateral

Unilineal descent systems

Unilineal Descent are the most common of all descent systems. These are generally named discrete and bounded. Membership in a UDG is usually obtained involuntarily by virtue of birth. In a UDG, the inheritance of property, rank and status, succession to titles and officers etc all follow a determinate lineal pattern. UDGs function as corporate groups exercising control over property, rights, obligations, privileges etc. UDGs have a formalized structure of authority, generally based on generation and age differences. On a higher plane, UDGs may serve as the locus for political power. Each UDG is exogamous thereby regulating marriage.         

Simple Unilineal Structure

Patrilineal Descent affiliates an individual with a group of kin who are related to him through his father alone. Thus, in Patrilineal systems, the children in each generation belong to the descent group of their father; their father, in turn, belongs to the descent group of his father; and so on. It is important to note that, although a man’s sons and daughters are all members of the same descent group, only the sons transmit affiliation to that group. The term Agnatic is often used for referring to transmission of descent in the male line.

Matrilineal Descent affiliates an individual with a group of kin who are related to her through her mother alone. Thus, in matrilineal systems, the children in each generation belong to the descent group of their mother; their mother, in turn, belongs to the descent group of her mother; and so on. It is important to note that, although a woman’s sons and daughters are all members of the same descent group, only the daughters transmit affiliation to that group. The term Uterine is often used for referring to transmission of descent in the female line

Both Patrilineal and Matrilineal rules of descent are unilineal rules; because an individual reckons descent through linkages with members of exclusively one sex only - either males only or females only. In a society with unilineal descent, the people refer themselves as belonging to a particular unilineal descent group because they believe all the members of that particular group to be related by virtue of common descent.

Differences between Patrilineal and Matrilineal Descent Systems

Although both Patrilineal and Matrilineal Systems are wings of the same unilineal structure, they are not mirror images of one another.

1.         Patrilineal systems combine the locus of authority and the channel for replacement in one source itself, i.e., men. By contrast, in matrilineal systems, while the locus of authority is in the hands of men, women are the channels for replacement.

2.         Patrilineal systems are principally interested in men while matrilineal systems are interested both in women and men.

3.         When we consider the role of men in the two systems, we find that in Patrilineal systems the ‘father’ have authoritative control while in Matrilineal systems the ‘brothers’ have control.

4.         When we consider the role of women in the two systems, we find that in patrilineal systems, it is the sisters of men who do it.

5.         In a Patrilineal system a man gains rights over the sexual, domestic and reproductive services of his wife while in a matrilineal system, he may gain rights over the first two but he cannot gain rights over the last because this right is vested with her matrilineages.

6.         a man gains complete rights over the possession of his own children in Patrilineal Systems, but he has no rights over them in matrilineal systems.

7.         From the point of view of the roles involved we find that in patrilineal systems, it is the father-son-brother constellation that predominates while in matrilineal systems. It is the mother-daughter-brother-sister constellation that dominates.

8.         When we consider the residential patterns, patrilineal systems are patrilocal but matrilineal systems are not simply matrilocal. Due to the major roles played by brothers and particularly mother’s brothers, avunculocality also occurs.

Robin Fox has very nicely pinpointed the differences and the complexities involved in the two types of unilineal systems. According to him, patrilineal systems do not present any problems because they manage to combine residence, descent and authority very neatly. But matrilineal systems are complicated and vulnerable. He characterizes the three basic kinds of matrilineal societies as follows: That based on the mother-daughter-sister roles and matrilocal residence. Here the burden of control and continuity is to some extent shifted onto the women, and in societies with this basis it is usually the case that women have higher prestige and influence than in the others. That based on the brother-sister-nephew roles, with avunculocal residence preferred, or, failing this, some means whereby the mother’s brother can control his nephews. In this type the status of women is usually lower, as control and continuity are monopolized by the men. That based on the full constellation of consanguine matrilineal roles mother-daughter, brother-sister, mother’s brother-sister’s son. Her control and continuity are primarily in the hands of the men, but the status of the women need not be low. It will perhaps be intermediate between that in 1 and 2.

Complex Unilineal Structures

Double Descent affiliates an individual with a group of kin who are related to him/her at the same time through both his/her father and mother, including only the patrilineal kin of his/her father and the matrilineal kin of his/her mother. A Double Descent System is thus a discrete combination of unilineal affiliation. The people in Double Descent System reckon patrilineal descent for certain purposes and matrilineal descent for certain other purposes. A Double Descent System works on the basis of distribution of rights and responsibilities between the two-unilineal descent groups. Conflict between the two-unilineal descent groups is thus avoided by conferring equal importance to both the groups.

Bilinear Kin Groups are the complex products of the combined operation of Double Descent organization and Dual organization. In consonance with the Double Descent organization, there are patrilineal groups and matrilineal groups. Each of these discrete unilineal descent groups are only two in number according to the moiety organization. The patri-moieties and the Matri-moieties get superimposed on one another to produce Bilinear Kin Groups. They have only four such Bilinear Kin Groups. Bilinear Kin Group organization is most commonly found type of kinship system in Australian societies.

Non-Unilineal Or Cognatic Systems

The Cognatic or Non-Unilineal Systems are of two types:

Ambilineal

In an Ambilineal system the affiliation of an individual to his/her kin is left at the choice of the individual whereby, he/she may reckon descent from a putative ancestor through any form of linkages with males or females or both. Ambilineal descent groups, also termed ramages. However, they also allow for individuals to chose group membership at least at one point in their lives. Reasons for assuming membership in one group or another usually depend on the availability of corporately owned lands, but will, of course, also be influenced by political factors and personal friendships among kin. Membership decisions are further complicated by additional options presented at marriage. People can choose to join husbands' or wives' groups rather than one of those traced through their natal families.

Bilateral

Bilateral kinship organization presents something of a classification problem as all societies recognize and interact with a variety of maternal and paternal kin on a regular basis. Thus, while members of unilineal societies rely exclusively on agnatic or uterine kin in certain formal situations, they also maintain both structured and informal relationships with nonunilineal kin and form bilateral kindreds for a variety of purposes. The universal occurrence of bilateral kinship, often in conjunction with unilineal institutions, has led to a variety of controversies as to whether bilateral structures exist as a general form or whether a specific society is unilineal or bilateral.

Bilateral Descent affiliates an individual with a group of kin who are related to him/her through both his/her father and mother. Thus, these kinsmen may include both the patri and the Matri kin of his/her father as well as both the Matri and the patri kin of his/her mother. Such a Bilateral Kin Group has been designated as Kindred. The term ‘Descent Group’ is generally avoided in this case, because a kindred is merely an ephemeral grouping, which is neither permanent nor a continuing one through generations in any fixed pattern. The reckoning of kindred changes with the individual who reckons his/her circle of relatives. Every individual in a society has kindred, and the kindred of each individual will over and with his her next of kin. No kindred are common for any two individuals besides siblings. A kindred is thus not ancestor - focused but ego - central.

Functions of Descent Groups

Unilineal descent groups tend to be ‘corporate’ in several senses. Their members may often come together for ritual and ceremonial functions, for instance, for collective worship of lineage gods, totems or ancestors.

The descent group will have a built-in authority structure, with power normally exercised by senior males, and it may well own corporate property. An individual’s economic rights and responsibilities will be defined by his or her position in the descent group.

In many societies, unilineal descent groups are also jural units, internally deciding their own disputes, and externally acting as a unified group in relation to other similar groups in the conduct of feud, etc. For this reason, lineage structure is often conterminous with the political structure in societies lacking a centralized state structure.