Cousin

 ( Family ) 

The degree is the number of generations subsequent to the common ancestor before a parent of one of the cousins is found. This means the degree is the separation of the cousin from the common ancestor less one. Also, if the cousins are not separated from the common ancestor by the same number of generations, the cousin with the smallest separation is used to determine the degree. The removal is the difference between the number of generations from each cousin to the common ancestor. Two people can be removed but be around the same age due to differences in birth dates of parents, children, and other relevant ancestors.

• The terms full cousin and are used to specify a first cousin with no removals.
• The terms cousin-uncle/aunt and cousin-niece/nephew are sometimes used to describe the direction of the removal of the relationship, especially in Mennonite, Indian, and Pakistani families. Adding uncle/aunt refers to an older generation while niece/nephew refers to younger ones. Another approach is to use the terms up and down to indicate direction of removal. For example, in the Basic family tree above, George would be a cousin-nephew of David, or a first cousin once removed down. David would be George's cousin-uncle, or cousin once-removed up. For additional removals, grand/great are applied to these relationships.
  Harry Loewen (1988). 083613463X, Herald Press. 083613463X
  Thus, David is a cousin-granduncle from Ingeborg's perspective, or a cousin twice removed that comes from an older generation, also known as a cousin twice removed up. Similarly, Ingeborg is a cousin-grandniece, or a female first cousin twice removed down, to David.
• The term is sometimes used for the grandchild of a first cousin, or the first cousin of a grandparent: a first cousin twice removed.
• The term kissing cousin is sometimes used for a distant relative who is familiar enough to be greeted with a kiss.

On the other hand, parallel and cross cousins are reciprocal relationships. Parallel cousins are descended from same-sex siblings. A parallel first cousin relationship exists when both the subject and relative are maternal cousins, or both are paternal cousins. Cross cousins are descendants from opposite-sex siblings. A cross first cousin relationship exists when the subject and the relative are maternal cousin and paternal cousin to each other. In the basic family tree example, David and Emma are cross cousins.

Double cousins are relatives who are cousins from two different branches of the family tree. This occurs when , respectively, reproduce with different siblings from another family. This may also be referred to as "cousins on both sides". The resulting children are related to each other through both their and are thus doubly related. Double first cousins share both sets of .

Half cousins are descended from half siblings and would share one grandparent. The children of two half siblings are first half cousins. If half siblings have children with another pair of half siblings, the resulting children would be double half first cousins and would share one grandparent on each side.

While there is no agreed upon term, it is possible for cousins to share three grandparents if a pair of half siblings had children with a pair of full siblings.

Step-cousins are either stepchildren of an individual's aunt or uncle, nieces and nephews of one's step-parent, or the children of one's parent's step-sibling. A cousin-in-law is the cousin of one's spouse or the spouse of one's cousin.

Between first cousins, there are two shared ancestors each with four generations of separation, up and down the family tree: $\backslash left(\backslash tfrac\{1\}\{2\}\backslash right)^4\; +\; \backslash left(\backslash tfrac\{1\}\{2\}\backslash right)^4$; their consanguinity is one-eighth. For each additional removal of the cousin relationship, consanguinity is reduced by half, as the generations of separation increase by one. For each additional degree of the cousin relationship, consanguinity is reduced by a quarter as the generations of separation increase by one on both sides.

Half cousins have half the consanguinity of ordinary cousins as they have half the common ancestors (i.e. one vs two). Double cousins have twice the consanguinity of ordinary cousins as they have twice the number of common ancestors (i.e. four vs two). Double first cousins share the same consanguinity as half-siblings. Likewise, double half cousins share the same consanguinity as first cousins as they both have two common ancestors. If there are half-siblings on one side and full siblings on the other, they would have three-halves the consanguinity of ordinary first cousins.

In a scenario where two monozygotic (identical) twins have children with another pair of monozygotic twins, the resulting double cousins would test as genetically similar as siblings.

Currently about 10% and historically as high as 80% of all marriages are between first or second cousins. Cousin marriages are often arranged. Anthropologists believe it is used as a tool to strengthen the family, conserve its wealth, protect its cultural heritage, and retain the power structure of the family and its place in the community. Some groups encourage cousin marriage while others attach a strong social stigma to it. In some regions in the Middle East, more than half of all marriages are between first or second cousins (in some of the countries in this region, this may exceed 70%). Just outside this region, it is often legal but infrequent. Many cultures have encouraged specifically cross-cousin marriages.