Second Cousin
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Second Cousin

Commonly "cousin" refers to a "first cousin", a relative whose most recent common ancestor with the subject is a grandparent.[1]. More generally, in the lineal kinship system used in the English-speaking world, a cousin is a type of familial relationship in which two relatives are two or more familial generations away from their most recent common ancestor.

Degrees and removals are used to more precisely describe the relationship between cousins. Degree measures the separation, in generations, from the most recent common ancestor to the closest of the cousins, while removal measures the difference between the generations the cousins are from. To illustrate usage, a "second cousin" is a cousin with a degree of two. When the degree is not specified first cousin is assumed. A cousin that is "once removed" is a cousin with one removal. When the removal is not specified no removal is assumed.[2][3] This definition distinguishes a cousin from an ancestor, descendant, sibling, aunt, uncle, niece, or nephew.[]

Various governmental entities have established systems for legal use that can precisely specify kinship with common ancestors any number of generations in the past, for example, in medicine and law, a first cousin is a type of third-degree relative.[]

Basic definitions

Basic family tree
JasonBeatrice
JamesHelenEugeneMary
NancyJosephJulieRoger
GordonLauraChristinaMatt
Sam{{{Blk}}}Lyla
The relationship between every solid shaded box and a similar one on the other branch of the tree is that of a cousin. The removal is the number of rows they are separated by. The degree of the relationship is that of the cousin with the lightest shading, the lightest shading represents a degree of one and increases with darkness. The rules are the same for cousin-in-laws, except they exist between shaded solid lines and shaded dotted lines.

People are related with a type of cousin relationship if they share a common ancestor, and the most recent common ancestor is two or more generations away from both people. This means neither person is an ancestor of the other, they do not share a parent (siblings), and neither is a sibling of a common ancestor (aunts/uncles and nieces/nephews).[3] In the English system the cousin relationship is further detailed by the concepts of degree and removal.

The degree is the number of generations subsequent to the common ancestor before a parent of one of the cousins is found. This means that the degree is the removal of the cousin from the common ancestor less one and that if the cousins aren't removed from the common ancestor by the same number of generations, the cousin with the smallest removal is used to determine the degree.[2] The removal is the difference between the number of generations from each cousin to the common ancestor.[2] Two people can be removed but be around the same age due to differences in birth dates of parents children and other relevant ancestors.[2][4][5]

To illustrate these concepts the following table is provided. This table identifies the degree and removal of cousin relationship between two people using their most recent common ancestor as the reference point and demonstrates it in the example family tree.

Removal is measured in number of generations from the most recent common ancestor
Relative's removal

Relative's relationship to the most recent common ancestor

Relationship

Example from Basic family tree ?

2

Grandparent

3

Great-grandparent

4

Great-great-grandparent

generations
Degree, Removal
Subject's removal

Subject's relationship to the most recent common ancestor

2

Grandparent

1st cousin

Joseph & Julie

1st cousin once removed

Joseph & Matt

1st cousin twice removed

Joseph & Lyla

1, (R - 2)
3

Great-grandparent

1st cousin once removed

Gordon & Julie

2nd cousin

Gordon & Matt

2nd cousin once removed

Gordon & Lyla

2, (R - 3)
4

Great-great-grandparent

1st cousin twice removed

Sam & Julie

2nd cousin once removed

Sam & Matt

3rd cousin

Sam & Lyla

3, (R - 4)
Subject's
removal
generations Degree, 1, (S - 2) 2, (S - 3) 3, (S - 4) (min(R, S) - 1), ||
Removal

Additional terms

The following is a list of less common cousin terms.

  • The terms full cousin[6] and cousin-german are used to specify a first cousin with no removals.[7]
  • The terms cousin uncle/aunt and cousin niece/nephew or second uncle/aunt/nephew/niece are sometimes used to describe the direction of the removal of the relationship in Mennonite families. This term relates to a first cousin once removed. For additional removals grand/great is applied to the niece/nephews/uncle/aunt relationship.[8] For example a second granduncle is a male first cousin twice removed that comes from a more primary (older) generation.

Gender-based distinctions

A maternal cousin is a cousin that is related to the mother's side of the family, while a paternal cousin is a cousin that is related to the father's side of the family. This relationship is not necessarily reciprocal, as the maternal cousin of one person could be the paternal cousin of the other. In the example Basic family tree Julie is Joseph's maternal cousin and Joseph is Julie's paternal cousin.

Parallel and cross cousins on the other hand are reciprocal relationships. Parallel cousins are descended from same-sex siblings. Cousins that are related to same-sex siblings of their most recent common ancestor are parallel cousins.[9] A parallel first cousin relationship exist 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 exist when the subject and the relative are maternal cousins and paternal cousin to each other. In the example Basic family tree Joseph and Julie are both cross cousins.

Multiplicities

GaryGlenda
JasonBeatrice
JamesHelenEugeneMary
Joseph{{{Blk}}}Julie
Joseph and Julie are double first cousins as they are cousins through both parents. They are cousins through the siblings James and Mary as well as the siblings Helen and Eugene.

Double cousins are relatives that are cousins on their maternal side and cousins on their paternal side. This occurs when siblings, respectively, reproduce with different siblings from another family.[10] This may also be referred to as 'cousins on both sides.' The resulting children are related to each other through both of their parents and are thus doubly related. Double first cousins share both sets of grandparents.

JasonBeatriceAnthony
JamesHelenCharlesJanet
JosephLilian
Joseph and Lilian are half cousins because their parents (Helen and Charles) are half-siblings, their grandmother (Beatrice) having remarried.

Half cousins are descended from half siblings and would share 1 grandparent.[11] 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.

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.[12][13]

Non-blood relations

JasonBeatrice
JamesHelenEugeneCorindaColin
Joseph{{{Blk}}}{{{Blk}}}Rachel
Joseph and Rachel are step-cousins because Joseph's uncle (Eugene) has become Rachel's stepfather as a result of Rachel's mother (Corinda) having remarried Eugene.

Step-cousins are either stepchildren of an individual's aunt or uncle, nieces and nephews of one's stepparent, or the children of one's parent's stepsibling.[] Cousin-in-laws are the cousins of a person's spouse or the spouse of a person's cousin.[14] Neither of these relationships has consanguinity. In the Basic family tree example Joseph and Roger are both Cousin-in-laws.

Consanguinity

Consanguinity is a measure of how closely individuals are related to each other. It is measured by the coefficient of relationship. Below, when discussing the coefficient of relationship, we assume the subject and the relative are only related through the kinship term. A coefficient of one represents the relationship you have with yourself. Consanguinity decreases by half for every generations of separation from the most recent common ancestor, as there are two parents for each child. When there is more than one common ancestor the consanguinity between each ancestor is added together to get the final result.[15]

Between first cousins there are two shared ancestors each with four generations of separation, up and down the family tree (), therefore their consanguinity is one-eighth. When the removal of the cousins relationship increases consanguinity is reduced by half, as the generations of separation increase by one. When the degree of the cousins relationship increases consanguinity is reduced by a quarter, as the generations of separation increase by one on both sides.[15]

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 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.[15]

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

Reproduction

Couples that possess higher than normal consanguinity, shared identical DNA and genetic material, have an increased chance of sharing genes for recessive traits.[16] Therefore, children of high consanguinity parents may have an increased risk of genetic disorders, particularly if their parents both carry a harmful recessive mutation. See inbreeding for more information.

Scientists through multiple studies have established a substantial and consistent positive correlation between the kinship of couples and the number of children and grandchildren they have. The 2008 deCODE study results show that couples related at the level of third cousins have the greatest number of offspring, with the greatest reproductive success observed for couples related at the level of third and fourth cousins.[17] This study provides the most comprehensive answer yet to the longstanding question of how kinship affects human fertility. The study result was somewhat counterintuitive from an evolutionary perspective because closely related parents have a higher probability of having offspring homozygous for deleterious recessive mutations, although closer parental kinship can also decrease the likelihood of immunological incompatibility between mother and offspring, for example in rhesus factor blood type.[18] The study confirmed that the offspring of first and second cousins died younger and reproduced less.[19]

Cousin marriage

Cousin marriage is important in several anthropological theories which often differentiate between matriarchal and patriarchal parallel and cross cousins.

Currently about 10% and historically as high as 80% of all marriages are between first or second cousins.[20][21] Cousin marriages are often arranged.[20][21][22][23][24] 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 over half of all marriages are between first and second cousins. In some of the countries in this region this may exceed 70%.[25] Just outside this region it is often legal but infrequent. Many cultures have encouraged specifically cross-cousin marriages.[26] In other places it is legally prohibited and culturally equivalent to incest.[27][28] Supporters of cousin marriage often view the prohibition as discrimination,[29][30] while opponents cite the potential immorality.[31]

See also

References

  1. ^ "Cousin". Brewer's Dictionary of Phrase & Fable. Chambers Harrap Publishers. 2013. 19.
  2. ^ a b c d "A Dictionary of Genetics". A Dictionary of Genetics. Oxford University Press. 2013. 8.
  3. ^ a b "Definition of Cousin by Merriam-Webster". merriam-webster.com. Merriam-Webster.
  4. ^ "What is a First Cousin, Twice Removed?". Genealogy.com. Retrieved 2015.
  5. ^ "Genetic And Quantitative Aspects Of Genealogy - Types Of Collateral Relationships". Genetic-genealogy.co.uk. Retrieved 2014.
  6. ^ "Full cousin definition and meaning | Collins English Dictionary". www.collinsdictionary.com. Retrieved .
  7. ^ "Cousin-german definition and meaning | Collins English Dictionary". www.collinsdictionary.com. Retrieved .
  8. ^ Harry Loewen (1988). Why I am a Mennonite: Essays on Mennonite identity. Herald Press. p. 286. ISBN 083613463X. They seemed to treasure genetic relations in a way I had not encountered before, using such relational designations as "cousin-uncle." They spoke of Mennonite names, Mennonite food, Low German, Russian immigration.
  9. ^ "Overview cross-cousin". Oxford reference. Retrieved 2020.
  10. ^ Dr. Barry Starr (2015-01-13). "Relatedness". Stanford at The Tech: Understanding Genetics.
  11. ^ Jillynne Quinn (2014-01-09). "Relatedness". Stanford at The Tech: Understanding Genetics.
  12. ^ Genetic And Quantitative Aspects Of Genealogy - Classification Of Relationships
  13. ^ part 7 G4BB: World of Tinker-Toys | Deep-Fried Hoodsie Cups
  14. ^ "cousin-in-law". Webster's Dictionary.
  15. ^ a b c "Genetic And Quantitative Aspects Of Genealogy - CALCULATION OF THE COEFFICIENT OF RELATIONSHIP". Genetic-genealogy.co.uk. Retrieved 2014.
  16. ^ The Conversation: What's the genetic disease risk for children of related couples? Date: September 27, 2012. Source: Tiong Tan, Clinical Geneticist at Victorian Clinical Genetics Services and Researcher in Craniofacial Research, Murdoch Children's Research Institute.
  17. ^ PubMed: An association between the kinship and fertility of human couples. Free Full Text. Date: 2008 Feb 8; Source: https://www.decode.com/publications/ deCODE Genetics.
  18. ^ Science Daily: Third Cousins Have Greatest Number Of Offspring, Data From Iceland Shows. Date: February 8, 2008; Source: deCODE genetics.
  19. ^ Nature: When kissing cousins are good for kids - A little inbreeding might boost fertility. By Heidi Ledford. Date: Published online 7 February 2008.
  20. ^ a b Kershaw, Sarah (26 November 2009). "Shaking Off the Shame". The New York Times.
  21. ^ a b "Go Ahead, Kiss Your Cousin - DiscoverMagazine.com".
  22. ^ Bittles, Alan H. (May 2001). A Background Summary of Consanguineous Marriage (PDF) (Technical report). Edith Cowan University.
  23. ^ Bittles 1994, p. 567
  24. ^ Bittles and Black 2009, Section 7
  25. ^ Dr. Alan Bittles; Dr. Michael Black. "Global prevalence". consang.net.
  26. ^ Moore, Alexander (1998). Cultural Anthropology: The Field Study of Human Beings. Rowman & Littlefield. p. 216. ISBN 9780939693481.
  27. ^ "The Surprising Truth About Cousins and Marriage". 14 February 2014.
  28. ^ Paul, Diane B.; Spencer, Hamish G. (23 December 2008). ""It's Ok, We're Not Cousins by Blood": The Cousin Marriage Controversy in Historical Perspective". PLOS Biology. 6 (12): 2627-30. doi:10.1371/journal.pbio.0060320. PMC 2605922. PMID 19108607.
  29. ^ "Final Thoughts". Cousin Couples. Retrieved 2016.
  30. ^ Brandon Keim (23 December 2008). "Cousin Marriage OK by Science". Wired.
  31. ^ Saletan, William (10 April 2002). "The Love That Dare Not Speak Its Surname" – via Slate.

External links


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