Parallel Cousins vs Cross Cousins
A cross cousin is maternal uncle's child or paternal aunt's child. A cross cousin is from the parent's opposite-sexed sibling. Cross Cousins are Mothers brothers children or fathers sisters children. Parallel Cousins are offspring of siblings of the same sex.
First cousins may either be the children of two brothers (patrilateral decent parallel cousins), of two sisters (matrilateral decent parallel cousins). In the Seri kinship system, cross cousins and parallel cousins are called by the same terms as those used for siblings.
The distinction between cross cousins and parallel cousins is often an extremely important one in traditional societies. In Iroquois system and among Hindus marriage is promoted between cross cousins.
In a patrilineage, parallel cousins are part of the subject's unilineal descent and cross cousins are not part of the subject's unilineal descent. In societies that are matrilineal, parallel cousins are considered to be related to the subject while cross cousins are not.
Cross-cousin marriage is preferred or even obligatory in some cultures, but marriage between parallel cousins often falls under incest and is a taboo. Cross-cousin marriage performed to strengthen alliances between clans. Sociologists and anthropologists have argued that cross-cousin marriage has a profound effect on social relations, in society and also in the family.
In south India it is a common practice for Hindu cross cousins to marry, with matrilateral cross-cousin marriages being usually favored. The Hindu cross-cousin marriages also a common practice in the other states of south India.
LÚvi-Strauss postulated that cross-cousin marriage had the two consequences of setting up classes which automatically delimit the group of possible spouses and of determining a relationship that can decide whether a prospective spouse is to be desired or excluded. Cross-cousin marriage is the only type of preferential union that can function normally and exclusively and still give every man and woman the chance to marry a cross-cousin. Cross-cousin marriage can be a normal form of marriage in a society, but the other systems can only be privileged forms.