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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 one of the cousins (whichever is closest), while removal measures the difference in generations between the cousins themselves. 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]

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.[ citation needed ]

Basic definitions

Basic family tree
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 the relatives are separated by. The degree of the relationship is that of the relative with the lowest order. 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 are separated from their most recent common ancestor by two or more generations. This means neither person is an ancestor of the other, they do not share a parent (are not 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 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. [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.

Relationship between subject/relative and example from Basic family tree given the relationship to their most resent common ancestor
Separation in generations to ancestor R→234
S↓Relationship to ancestor Grandparent Great-grandparentGreat-great-grandparent
2 Grandparent 1st cousin1st cousin once removed1st cousin twice removed
David & EmmaDavid & GeorgeDavid & Imogen
3Great-grandparent1st cousin once removed2nd cousin2nd cousin once removed
Frank & EmmaFrank & GeorgeFrank & Imogen
4Great-great-grandparent1st cousin twice removed2nd cousin once removed3rd cousin
Harry & EmmaHarry & GeorgeHarry & Imogen
For cousins (R & S ≥ 2): Degree, Removal = (min(R, S) − 1), |R − S| where R and S is the separation

Additional terms

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 Emma is David's maternal cousin and David is Emma'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. [10] 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 cousins and paternal cousin to each other. In the example Basic family tree David and Emma are both cross cousins.


Ewan and Fannie are double first cousins because they share both sets of grandparents as they are cousins through both parents. They are cousins through the siblings Claude and Darrell as well as the siblings Colleen and Dorothea.

Double cousins are relatives that are cousins from two different branches of the family tree. This occurs when siblings, respectively, reproduce with different siblings from another family. [11] This may also be referred to as "cousins on both sides". The resulting children are related to each other through both their parents and are thus doubly related. Double first cousins share both sets of grandparents.

David and Esme are half cousins as they share only one grandparent (Agatha) because they are related through half-siblings (Betty and Cyrus).

Half cousins are descended from half siblings and would share one grandparent. [12] 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. [13] [14]

Non-blood relations

David and Evangeline are step-cousins because David's uncle (Charles) is now Evangeline's stepfather, Evangeline's mother (Corinda) having married Charles.

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. [15] A cousin-in-law is the cousin of a person's spouse or the spouse of a person's cousin. [16] In the Basic family tree example David and Edward are both cousins-in-law. None of these relationships have 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 related only 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. [17]

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. [17]

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. [17]

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.


Offspring of first and second cousins die younger and reproduce less. [18] Couples that are closely related have an increased chance of sharing genes, including mutations that occurred in their family tree. If the mutation is a recessive trait it will not reveal itself unless both father and mother share it. [19] Due to the risk that the trait is harmful, children of high consanguinity parents have an increased risk of recessive genetic disorders. See inbreeding for more information.

Closely related couples have more children. Couples related with consanguinity equivalent to that of third cousins have the greatest reproductive success. [20] This seems counter-intuitive as closely related parents have a higher probability of having offspring that are unfit, yet closer kinship can also decrease the likelihood of immunological incompatibility during pregnancy. [21]

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. [22] [23] Cousin marriages are often arranged. [22] [23] [24] [25] [26] 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 and second cousins. In some of the countries in this region this may exceed 70%. [27] Just outside this region it is often legal but infrequent. Many cultures have encouraged specifically cross-cousin marriages. [28] In other places it is legally prohibited and culturally equivalent to incest. [29] [30] Supporters of cousin marriage often view the prohibition as discrimination, [31] [32] while opponents cite the potential immorality [33] and the increased rate of birth defects in children of cousin marriages.

See also

Related Research Articles

Incest is human sexual activity between family members or close relatives. This typically includes sexual activity between people in consanguinity, and sometimes those related by affinity, adoption, clan, or lineage.

Inbreeding Production of offspring from the mating of individuals of a breed who are more closely related than the average members of the breed.

Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity.

An incest taboo is any cultural rule or norm that prohibits sexual relations between certain members of the same family, mainly between individuals related by blood. All human cultures have norms that exclude certain close relatives from those considered suitable or permissible sexual or marriage partners, making such relationships taboo. However, different norms exist among cultures as to which blood relations are permissible as sexual partners and which are not. Sexual relations between related persons which are subject to the taboo are called incestuous relationships.

Kinship Human relationship term; web of social relationships that form an important part of the lives of most humans in most societies; form of social connection

In anthropology, kinship is the web of social relationships that form an important part of the lives of all humans in all societies, although its exact meanings even within this discipline are often debated. Anthropologist Robin Fox states that "the study of kinship is the study of what man does with these basic facts of life – mating, gestation, parenthood, socialization, siblingship etc." Human society is unique, he argues, in that we are "working with the same raw material as exists in the animal world, but [we] can conceptualize and categorize it to serve social ends." These social ends include the socialization of children and the formation of basic economic, political and religious groups.

A sibling is a gender neutral word for a relative that shares at least one parent with the subject. A male sibling is a brother and a female sibling is a sister. In most societies throughout the world, siblings often grow up together, thereby facilitating the development of strong emotional bonds. Sometimes, they may grow up apart in foster care. The emotional bond between siblings is often complicated and is influenced by factors such as parental treatment, birth order, personality, and personal experiences outside the family.

The Serbo-Croatian standard languages have one of the more elaborate kinship (srodstvo) systems among European languages. Terminology may differ from place to place. Most words are common to other Slavic languages, though some derive from Turkish. The standardized languages may recognize slightly different pronunciations or dialectical forms; all terms are considered standard in all language standards, unless otherwise marked: [S] (Serbian), [C] (Croatian), [B] (Bosnian) and [M] (Montenegrin) below.

Consanguinity Property of being from the same kinship as another person

Consanguinity is the property of being from the same kinship as another person. In that aspect, consanguinity is the quality of being descended from the same ancestor as another person.

An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or (recursively) the parent of an antecedent. Ancestor is "any person from whom one is descended. In law the person from whom an estate has been inherited."

The coefficient of relationship is a measure of the degree of consanguinity between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, and was derived from his definition of the coefficient of inbreeding of 1921. The measure is most commonly used in genetics and genealogy. A coefficient of inbreeding can be calculated for an individual, and is typically one-half the coefficient of relationship between the parents.

In genealogy, pedigree collapse describes how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree of their offspring to be smaller than it could otherwise be. Robert C. Gunderson coined the term; synonyms include implex and the German Ahnenschwund.

In Catholic canon law, affinity is an impediment to marriage of a couple due to the relationship which either party has as a result of a kinship relationship created by another marriage or as a result of extramarital intercourse. The relationships that give rise to the impediment have varied over time. Marriages and sexual relations between people in an affinity relationship are regarded as incestuous.

A person's next of kin (NOK) is that person's closest living blood relative or relatives. Some countries, such as the United States, have a legal definition of "next of kin". In other countries, such as the United Kingdom, "next of kin" may have no legal definition and may not necessarily refer to blood relatives at all.

In law and in cultural anthropology, affinity is the kinship relationship created or that exists between two people as a result of someone's marriage. It is the relationship which each party to a marriage has to the relations of the other partner to the marriage, but it does not cover the marital relationship itself. Laws, traditions and customs relating to affinity vary considerably, sometimes ceasing with the death of one of the marriage partners through whom affinity is traced, and sometimes with the divorce of the marriage partners. In addition to kinship by marriage, "affinity" can sometimes also include kinship by adoption or a step relationship.

Chinese kinship

The Chinese kinship system is classified as a "Sudanese" or "descriptive" system for the definition of family. Identified by Lewis Henry Morgan in his 1871 work Systems of Consanguinity and Affinity of the Human Family, the Sudanese system is one of the six major kinship systems together with Eskimo, Hawaiian, Iroquois, Crow, and Omaha.

Cousin marriage Marriage between those with common grandparents or other recent ancestors

A cousin marriage is a marriage where the partners are cousins. The practice was common in earlier times, and continues to be common in some societies today, though in some jurisdictions such marriages are prohibited. Worldwide, more than 10% of marriages are between first or second cousins. Cousin marriage is an important topic in anthropology and alliance theory.

In law, a prohibited degree of kinship refers to a degree of consanguinity and sometimes affinity between persons that results in certain actions between them being illegal. Two major examples of prohibited degrees are found in incest and nepotism. Incest refers to sexual relations and marriage between closely related individuals; nepotism is the preference of blood-relations in the distribution of a rank or office.

Kinship terminology is the system used in languages to refer to the persons to whom an individual is related through kinship. Different societies classify kinship relations differently and therefore use different systems of kinship terminology; for example, some languages distinguish between consanguine and affinal uncles, whereas others have only one word to refer to both a father and his brothers. Kinship terminologies include the terms of address used in different languages or communities for different relatives and the terms of reference used to identify the relationship of these relatives to ego or to each other.

Family group of people affiliated by consanguinity, affinity, or co-residence

In human society, family is a group of people related either by consanguinity or affinity. The purpose of families is to maintain the well-being of its members and of society. Ideally, families would offer predictability, structure, and safety as members mature and participate in the community. In most societies, it is within families that children acquire socialization for life outside the family. Additionally, as the basic unit for meeting the basic needs of its members, it provides a sense of boundaries for performing tasks in a safe environment, ideally builds a person into a functional adult, transmits culture, and ensures continuity of humankind with precedents of knowledge.

Laws regarding incest vary considerably between jurisdictions, and depend on the type of sexual activity and the nature of the family relationship of the parties involved, as well as the age and sex of the parties. Besides legal prohibitions, at least some forms of incest are also socially taboo or frowned upon in most cultures around the world.

Sesotho – the language of the Basotho ethnic group of South Africa and Lesotho – has a complex system of kinship terms which may be classified to fall under the Iroquois kinship pattern. The complex terminology rules are necessitated in part by the traditional promotion of certain forms of cousin marriage among the Bantu peoples of sub-Saharan Africa. Most of the terms used have common reconstructed Proto-Bantu roots.


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