Cousin

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For other uses, see Cousin (disambiguation).

"Nephew" redirects here. For the Danish band, see Nephew (band).

In genealogy, a cousin is  a relative, other than an  ancestor or  descendant, who shares a common ancestor. The term cousin is  often used more  specifically, to refer to a first cousin, the child of one's aunt or  uncle. Even when the more  general sense is  used, the term is  rarely applied to siblings, siblings of ancestors, or  descendants of siblings, because more  common terms are  in use for such relations (e.g., brother, sister, aunt, uncle, nephew, niece).

A cousin chart, or  table of consanguinity, is  a chart that identifies cousin relationships using a most recent common ancestor as a reference point. In principle, any two individuals with a common ancestor have  a cousin relationship — except if one of the individuals' parents is  a common ancestor, in which case a different set of terminology — mother, niece, uncle, brother and  so on — is  used. Note that this chart implicitly ranks relationships based on shared ancestry, a ranking that might not apply to all cultures. Some cultures draw a strong distinction between adoptive and  biological parents, or  between older and  younger siblings; neither distinction is  reflected here, though even in English such complexities can be conveyed using clarifying adjectives and  other modifiers. Conversely, some cultures do not distinguish between blood relations and  relations by marriage; this chart does not even include the latter.

Contents 1 Family tree 2 Determining cousin type 3 Double cousins and  half cousins 4 Chart 4.1 Chart relationships as sentences 5 Mathematical definitions 6 Alternative Canon Law Charts 7 References 8 See also 9 External links

[edit] Family tree

The family tree at right shows the relationship of each person to the orange person, with cousins colored in green. When referring to someone as a cousin, additional modifying words are  used to clarify the exact relationship between the two people. First and  second cousins for instance, use ordinal numbers to specify the number of generations between individuals and  a common ancestor. Examples of additional modifying phrases include "first cousins once removed", "double cousins", and  "half cousins".

[edit] Determining cousin type

The name of the cousinship is  not determined by oneself, but rather is  always determined by the generational level of the individual most closely related to the ancestor in common. Cousinship is  actually a description of three individual's relationships with each other. Oneself, the cousin, and  the ancestor in common. The following assumes there are  no double cousins:

Step 1: To work out if two people are  first, second, or  third cousins, count back the generations to their common ancestor. For example, if the common ancestor is  one's grandmother, that is  two generations. If it  is one's great-grandmother, that is  three generations.

Step 2: Take the closest descendant of the common ancestor. For example, if one of the cousins is  a great-great-grandchild (four generations) and  the other is  a grandchild, just consider the grandchild for now.

Step 3: If the closest descendant of the common ancestor is  a grandchild (two generations), the cousins are  first cousins; if three generations, second cousins, and  so on.

Step 4: If the cousins are  both separated from the common ancestor by the same number of generations, there is  no "removed". If the number of generations from the common ancestor is  different, that difference is  the number of "removed"s.

For example, if one is  a grandchild of (2 generations from) the common ancestor, and  one's cousin is  a great-great-grandchild of (4 generations from) the common ancestor, then one and  one's cousin are  first cousins twice removed.

Note that the above system is  symmetric; if person A is  person B's second cousin once removed, then person B is  person A's second cousin once removed as well, even though the relationship between them is  not symmetric (since the two are  not from the same generation).

Also note that much of this terminology is  variable; for example, many dictionaries give "a child of one's first cousin" as a secondary sense for the term second cousin (the primary sense being "a child of a first cousin of one's parent").

[ and  half cousins">edit] Double cousins and  half cousins

Generally, one's cousinship to another is  determined by a connection through only one parent to an  individual in that parent's biological family. But an  individual's cousinship to another individual may be determined by a connection through both parents. These cousins are  biologically connected to both the maternal and  paternal family trees and  that cousinship is  termed a double cousin. Another term is  cousins on both sides.

If a pair of siblings from one family each form a couple with a pair of siblings from another family, then the children of these two couples will be double first cousins to one another. They would already automatically be first cousins due to the fact that they are  children of one of their parent's siblings, but in this case the children of their mother's sibling, are  also the children of their father's sibling, and  thus they are  double first cousins.

Whether the first family siblings are  brother and  sister forming a coupling with a sister and  brother of the second family, or  whether the first family sibling pair are  brothers forming a coupling with a pair of sisters from the second family, whenever two siblings from one family each form a couple with two siblings from another family, the offspring of these two couples will be double first cousins to one another. Instead of the 12.5% consanguinity that first cousins share with each other, double first cousins share a 25% consanguinity with each other. If identical twins form a coupling with a corresponding member of another set of identical twins, the children of these two couples, though legally (double)first-cousins to one another would genetically be as closely related to each other as full siblings of a non-twin set of parents would be to each other.

Sometimes the children of these unions would be called cousin-siblings, cousin-brothers, or  cousin-sisters.

Note that no incest has occurred to create these close kinships.

Half-siblings share only one parent. Extrapolating, 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 but these terms though technically correct are  rarely used in practice. While it  would not be unusual to hear of another's half-brother, or  half-sister, so described, in common usage one would rarely hear of another's half-cousins or  half-aunt, so described, and  instead hear them described simply as the other's cousin or  aunt.

[edit] Chart

The chart below helps explain cousin relationships.

The closest relationship prevails - note that cousinship is  not calculated between individuals when one is  descended from the other, for example, two individuals are  not called cousins if they are  any degree of grandparent, parent and  child. Also cousinship is  not calculated between individuals of any degree of aunt/uncle and  nephew/niece relationship to each other.

If one person's →		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 ↘
Grandparent		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		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		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		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		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		first cousins five times removed	Second cousins four times removed	third cousins thrice removed	fourth cousins twice removed	fifth cousins once removed	Sixth cousins

[edit] Chart relationships as sentences

Reminder: the closest relationship prevails - note that cousinship is  not calculated between individuals when one is  descended from the other, for example, two individuals are  not called cousins if they are  any degree of grandparent, parent and  child. Also cousinship is  not calculated between individuals of any degree of aunt/uncle and  nephew/niece relationship to each other.

• If our parents are  siblings we are  first cousins, and  have the same grandparents
• If our grandparents are  siblings we are  second cousins and  have the same great grandparents
• If our great grandparents are  siblings we are  third cousins and  have the same great-great grandparents

• My first cousin's child and  I are  first cousins once removed to each other (one generation difference between us)
• My first cousin's grandchild and  I are  first cousins twice removed to each other (two generations difference between us)

Similarly

• My parent's first cousin and  I are  first cousins once removed to each other (one generation difference between us)
• My grandparent's first cousin and  I are  first cousins twice removed to each other (two generations difference between us)

• My second cousin's child and  I are  second cousins once removed to each other (one generation difference between us)
• My second cousin's grandchild and  I are  second cousins twice removed to each other (two generations difference between us)

Similarly

• My parent's second cousin and  I are  second cousins once removed to each other (one generation difference between us)
• My grandparent's second cousin and  I are  second cousins twice removed to each other (two generations difference between us)

Following this pattern, it  can be determined that xth cousin y-times removed means either of the following:

• The xth cousin of your direct ancestor y generations previously (eg. your great-grandparent's fifth cousin is  your fifth cousin thrice removed); or
• Your xth cousin's direct descendant y generations away (eg. your fifth cousin's great-grandchild is  also your fifth cousin thrice removed)

[edit] 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.

The mathematical definition is  more elegant if you always express consanguinity as the ordered pair of natural numbers (x, y) as defined above. In that case, the relationship one has with oneself is  (0, 0), the relationship between parent and  child is  (0, 1), and  the relationship between grandparent and  grandchild is  (0, 2). The relationship between siblings is  (1, 0); and  between aunt/uncle and  nephew/niece is  (1, 1). First cousins are  (2, 0). The first number expresses how many generations back the two people's most recent common ancestor is, while the second number expresses the generation difference between the two people.

[edit] Alternative Canon Law Charts

Another visual chart used in determining the legal relationship between two people who share a common ancestor (blood) is  based upon a diamond shape, and  is usually referred to as a Canon Law Relationship Chart.

The chart is  used by placing the "Common Progenitor" (the person from which both people are  descended) in the top space within the diamond shaped chart, and  then following each line down the outside edge of the chart. Upon reaching the final place along the opposing outside edge for each person, the relationship is  the determined by following that line inward to the point where the lines intersect. The information contained in the common "intersection" defines the relationship.

For a simple example, in the illustration to the right, if two siblings wanted to use the chart to determine their relationship using the chart to the right, their common parents would be placed in the top most position and  each child assigned the space below and  along the outside of the chart. Then, following the spaces inward, the two would meet in the "brother (sister)" diamond. If their children would want to determine their relationship, they would follow the path established by their parents, but descend an  additional step below along the outside of the chart (showing that they are  grandchildren of the "Common Progenitor"; following their respect lines inward, they would come to rest in the space marked "1st cousin". In cases where one side descends the outside of the diamond further than the other side because of additional generations removed from the "Common Progenitor", following the lines inward shows both the cousin rank (1st cousin, 2nd Cousin) plus the number of times (generations) "removed".

In the example provided at the right, generations one (child) through ten (8th Great Grandchild) from the Common Progenitor are  provided, however the format of the chart can easily be expanded to accommodate any number of generations needed to resolve the question of relationship.

[edit] References

[edit] See also

• Kinship terminology
• Cousin couple
• Consanguinity
• Family
• Most recent common ancestor
• Parallel cousin
• Cross cousin
• Genealogical numbering systems

[edit] External links

• Geneology.com definition of various cousins
• Geneology.com: What makes a cousin?
• Dictionary.com definition of "cousin"
• Dictionary.com definition of "great uncle"