Cousin chart: Encyclopedia - Cousin chart

Cousin chart

A cousin chart is the common name for a Table of Consanguinity. It identifies the correct name for the relationship between two people using their closest common ancestor as a reference point. This chart uses formal English relationship terms. For a general overview of kinship terminology, see the appropriate section in the article Family.

The term cousin typically refers to the child of one's parent's sibling (i.e. one's aunt or uncle). This is more precisely termed a "first cousin".

More generally, "cousins" are any relatives that are neither siblings nor direct descendents/ancestors. Ordinal numbers (first, second, third, etc) are used to quantify in which preceding generation the common direct ancestor is located. The term is then completed with a number removed, which indicates how many generations separate the relatives in question.

Thus, if one of John's great-great-grandparents is also one of Mary's great-great-great-great-grandparents, John and Mary are "third cousins twice removed". In purely mathematical terms, a sibling could be defined as a "zeroth cousin", and a niece/nephew–aunt/uncle relationship could be described as "zeroth cousins once removed"; however such terms are never used.

The chart below helps explain cousin relationships. Note that in informal usage, a granduncle is often called a great uncle and a grandaunt is often called a great aunt.

^* Here, "grandniece" is used as an abbreviation to indicate that they are each other's "grandniece/grandnephew & grandaunt/granduncle"

Cousin chart - Mathematical definitions

The family relationship between two individuals a and b, where G_a and G_b respectively are the number of generations between each individual and their nearest common ancestor, can be calculated by the following:

• If x=0 and y=0 then they are the same person.
• If x=0 and y=1 then they are parent and child.
• If x=0 and y=2 then they are grandparent and grandchild.
• If x=0 and y>2 then they are great ... great-grandparent and great ... great-grandchild, with y−2 greats.

• If x=1 and y=0 then they are siblings (brothers or sisters).
• If x=1 and y=1 then they are uncle/aunt and nephew/niece.
• If x=1 and y>1 then they are great ... great uncle/aunt and great ... great nephew/niece, with y−1 greats.

• If x>1 and y=0 then they are (x−1)^th cousins.
• If x>1 and y>0 then they are (x−1)^th cousins y times removed.

So two people sharing a pair of grandparents have x=2 and y=0 and are described as being first cousins.

If x>0 and they only share one nearest common ancestor rather than two, then the word "half" is sometimes added at the beginning of the relationship.

Cousin chart - Half cousins and double cousins

It should be noted that the above chart is inadequate to explain the relationships which result when two people are both descended from a single common ancestor, but each from a different partner of that common ancestor. Half-siblings are a familiar concept to most people. But it can also be extrapolated out in the same manner as other cousin relationships. For example, if one of John's parents and one of Mary's parents are half-siblings, then John and Mary are half-cousins. The half sibling of each of their respective parents would be their half-aunt or half-uncle.

It is also of note that two people can be related in more than one way. For example, if John and Mary are a couple, and John's brother Jake and Mary's sister Melinda are also a couple, then the children of the two respective unions would be double cousins. Jake and Melinda would be the double uncle and double aunt, respectively, to John and Mary's children. Note that no incest has occured in this scenario to create these unusual and close kinships. If Mary and Melinda are identical twins and John and Jake are identical twins, the double cousins would be genetically indistinguishable from biological siblings.

See also

• Consanguinity
• Family

Category: Kinship and descent

Adapted from the Wikipedia article "Cousin chart", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki