Cousin chart

From Wikipedia, the free encyclopedia.

A cousin chart identifies the correct name for the relationship between two people with a common ancestor. 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. 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.

If one person's →		Parent	Grandparent	Great Grandparent	Great Great Grandparent	Great Great Great Grandparent	Great Great Great Great Grandparent	Great Great Great Great Great Grandparent
is the other person's ↓	then they're ↘
Parent		Siblings	Niece/Nephew & Aunt/Uncle	Grandniece*	Great Grandniece*	Great Great Grandniece*	Great Great Great Grandniece*	Great Great Great Great Grandniece*
Grandparent		Niece/Nephew & Aunt/Uncle	First Cousins	First Cousins Once Removed	First Cousins Twice Removed	First Cousins Thrice Removed	First Cousins Four Times Removed	First Cousins Five Times Removed
Great Grandparent		Grandniece*	First Cousins Once Removed	Second Cousins	Second Cousins Once Removed	Second Cousins Twice Removed	Second Cousins Thrice Removed	Second Cousins Four Times Removed
Great Great Grandparent		Great Grandniece*	First Cousins Twice Removed	Second Cousins Once Removed	Third Cousins	Third Cousins Once Removed	Third Cousins Twice Removed	Third Cousins Thrice Removed
Great Great Great Grandparent		Great Great Grandniece*	First Cousins Thrice Removed	Second Cousins Twice Removed	Third Cousins Once Removed	Fourth Cousins	Fourth Cousins Once Removed	Fourth Cousins Twice Removed
Great Great Great Great Grandparent		Great Great Great Grandniece*	First Cousins Four Times Removed	Second Cousins Thrice Removed	Third Cousins Twice Removed	Fourth Cousins Once Removed	Fifth Cousins	Fifth Cousins Once Removed
Great Great Great Great Great Grandparent		Great Great Great Great Grandniece*	First Cousins Five Times Removed	Second Cousins Four Times Removed	Third Cousins Thrice Removed	Fourth Cousins Twice Removed	Fifth Cousins Once Removed	Sixth Cousins

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

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:

x = min (G_a,G_b)

y = |G_a-G_b|

• 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.

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 senario to create these unusual and close kinships.

See also

• Family
• Consanguinity