In 1984, Giles-Sims and  David Finkelhor  categorized and evaluated five possible hypotheses that could explain the Cinderella effect: "social-evolutionary theory," "normative theory," "stress theory," "selection factors," and "resource theory." The social-evolutionary theory is based on the proposal that non-genetically related parents will invest less in costly parental duties, due to the fact that their genes are not being passed on by that individual. The normative theory proposes that, due to genetic repercussions, incest among genetically related individuals is a widespread taboo and would thus be less common among biological relatives. They propose that incest among step families would be less taboo, since there is no risk of genetic degradation. The stress theory proposes that increased stressors, which are inherently more common among stepfamilies, cause an increased risk of abuse. The selection factors theory proposes that individuals who are likely to be stepparents (divorcees) are likely to be inherently more violent due to emotional disturbances, aggressive impulses, and self-esteem issues. Due to this, stepparents as a group would have a higher proportion of individuals with violent-prone characteristics, which would suggest that the abuse is happening due to personality factors, rather than the step-parental relationship directly. Finally, according to resource theory, individuals who contribute resources are granted authority, while individuals who lack resources are denied authority and more likely to resort to violence to obtain authority. It is therefore hypothesized that stepparents who are able to contribute resources to a family and have those resources be accepted by the family are less likely to be abusive. However, this hypothesis had yet to be tested directly on step families. [ 43 ]


Discussing the implications of this line of research, Australian psychologist Greg Tooley, author of a 2006 study confirming the existence of the effect, [ 28 ]  confessed that "it is certainly difficult to talk about because it is such a hot issue". [ 44 ]


Recognized


A  civil union  (also known as a  civil partnership ) is a legally recognized arrangement similar to  marriage , created primarily as a mean to provide recognition in law for  same-sex couples . Civil unions grant some or all of the rights of marriage (with  child adoption  being a common exception).


Civil unions have been established by law in several, mostly  developed , countries in order to provide legal recognition of relationships formed by same-sex couples and to afford them rights, benefits, tax breaks, and responsibilities. In 1989,  Denmark  was the first country to legalise civil unions; however, most other developed democracies did not begin establishing them until the 1990s and early 2000s. In  Brazil , civil unions were first created for opposite-sex couples in 2002, and then expanded to include same-sex couples in 2011. In the majority of countries that established same-sex civil unions, they have since been either supplemented or replaced by  same-sex marriage . Civil unions are viewed by  LGBT rights  campaigners as a "first step" towards establishing same-sex marriage, as civil unions are viewed by supporters of LGBT rights as a " separate but equal " status.


Many jurisdictions with civil unions recognize foreign unions if those are essentially equivalent to their own; for example, the  United Kingdom  lists equivalent unions in the  Civil Partnership Act 2004 Schedule 20 . The marriages of same-sex couples performed abroad may be recognized as civil unions in jurisdictions that only have the latter.


The terms used to designate civil unions are not standardised and vary widely from country to country.  Government-sanctioned relationships that may be similar or equivalent to civil unions include  civil partnerships ,  registered partnerships ,  domestic partnerships ,  significant relationships ,  reciprocal beneficiary relationships ,  common-law marriage ,  adult interdependent relationships ,  life partnerships ,  stable unions ,  civil solidarity pacts , and so on. The exact level of rights, benefits, obligations, and responsibilities also varies, depending on the laws of a particular country. Some jurisdictions allow same-sex couples to adopt, while others forbid them to do so, or allow adoption only in specified circumstances.


In the  United States , the term  civil union  was introduced in the state of  Vermont  in 2000 to connote a status equivalent to marriage for same-sex couples; it was chosen by the state's legislators in preference to phrases such as  "domestic partner relationship" or "civil accord". [ 2 ]


Domestic partnership , offered by some states, counties, cities, and employers since as early as 1985, [ 3 ]  has generally connoted a lesser status with fewer benefits. [ 4 ]   However, the legislatures of the  West Coast  states of  California ,  Oregon  and  Washington  have preferred the term  domestic partnership  for enactments similar or equivalent to civil union laws in  East Coast  states.


Civil unions are not seen as a replacement for marriage by many in the LGBT community. "Marriage in the United States is a civil union; but a civil union, as it has come to be called, is not marriage", said  Evan Wolfson  of  Freedom to Marry . [ 5 ]   "It is a proposed hypothetical legal mechanism, since it doesn't exist in most places, to give some of the protections but also withhold something precious from gay people. There's no good reason to do that."  However, some opponents of same-sex marriage claim that civil unions rob marriage of its unique status; Randy Thomasson, executive director of the Campaign for California Families, calls civil unions "homosexual marriage by another name" and contends that civil unions provide same-sex couples "all the rights of marriage available under state law". [ 6 ]   The California Supreme Court, in the  In Re Marriage Cases  decision, noted nine differences [ 7 ]  in state law.


Civil unions are commonly criticised as being ' separate but equal '; critics such as former  New Zealand  MP and feminist  Marilyn Waring  note that same-sex couples remain excluded from the right to marry and are forced to use a separate institution. [ 8 ]  Supporters of same-sex marriage contend that treating same-sex couples differently from other couples under the law allows for inferior treatment and that if civil unions were the same as marriage there would be no reason for two separate laws. A New Jersey commission which reviewed the state's civil union law reported that the law "invites and encourages unequal treatment of same-sex couples and their children". [ 9 ]  Some have suggested that creating civil unions which are open to opposite-sex couples would avoid the accusations of apartheid. [ 10 ]


Proponents of civil unions say that they provide practical equality for same-sex couples and solve the problems over areas such as hospital visitation rights and transfer of property caused by lack of legal recognition. [ 11 ]  Proponents also say that creating civil unions is a more pragmatic way to ensure that same-sex couples have legal rights as it avoids the more controversial issues surrounding marriage and the claim that the term has a religious source.


Many supporters of same-sex marriage state that the word 'marriage' matters and that the term 'civil union' (and its equivalents) do not convey the emotional meaning or bring the respect that comes with marriage. [ 9 ] [ 12 ]  Former US Solicitor General and attorney in the  Perry v. Schwarzenegger  case  Theodore Olsen  said that recognizing same-sex couples under the term 'domestic partnership' stigmatizes gay people's relationships, treating them as if they were "something akin to a commercial venture, not a loving union". [ 13 ]  Many also contend that the fact that civil unions are often not understood can cause difficulty for same-sex couples in emergency situations. [ 14 ]


As of July 18, 2024, the states that provide civil unions but not marriage for same-sex couples are:


In  Israel , no national domestic authority performs same-sex marriage, though couples may marry abroad. In addition, same-sex couples may be considered to have a  common-law marriage , which affords "most" of the rights of marriage. [ 15 ]


The following is a list of countries and other jurisdictions which have established civil unions for same-sex couples or opposite-sex couples, categorized by continent, with the year in which the law establishing civil unions in the listed country or other jurisdiction came into effect in brackets:


Several countries used to offer civil unions only for same-sex couples. The laws that allowed civil unions were repealed when same-sex marriage was legalized. The following is a list of countries and other jurisdictions that used to offer civil unions for same-sex couples with the years in which they were available in brackets:


Since 2003, the Argentine province of  Río Negro  and the city of  Buenos Aires  allow domestic partnerships. The City of  Villa Carlos Paz  (Córdoba) allowed it from 2007. Since 2009, the city of  Río Cuarto  (Córdoba) allows Civil Unions.


All levels of Australian Governments under nearly all Australian statutes do recognise same-sex couples as de facto couples as unregistered co-habitation or de facto status since 2009. [ 118 ]  From 1 July 2009 Centrelink recognised same-sex couples equally regarding social security – under the common-law marriage, de facto status or unregistered cohabitation. [ 119 ]


Registered relationship recognition in state Governments:


Registered relationship  recognition in 5 local government areas within Australia:


Cohabitation grants 112 benefits as family entities in Brazil since 2002. It is known as  união estável  when both parts are legally authorized to marry, and as  concubinato  when at least one party is legally prohibited from doing so. [ 125 ]  Cohabitation grants all rights marriage confers, with the exception of automatic opt-in for one of four systems of property share married couples have access to, and automatic right to inheritance. Potential confusion might arise regarding terminology, given how when Brazilian Portuguese refers to the term  união civil , it tends to be short for  casamento civil , or civil marriage.


Couples that have at least one child registered as a descendant of both parties might also have access to  união estável  or  concubinato  rights.


Same-sex stable cohabitation in Brazil is legally recognized nationwide since May 5, 2011. Brazil's Supreme Court voted 10–0 with one abstention to allow  same-sex couples  the same legal rights as married couples, following pointed recognition of such relationships that dates as far back as 2004. The ruling gave same-sex couples in such relationships the same financial and social rights enjoyed by those in mixed-sex ones. [ 126 ]


A union between two women and one man was reported in August 2012, though its legality was doubted. [ 127 ]


In  Canada :


were extended to same-sex couples before the enactment of the federal  Civil Marriage Act  which legalized  same-sex marriage in Canada  nationally.


The 1994 proposed  Equality Rights Statute Amendment Act  in  Ontario  was a notable early attempt to introduce a status similar to civil unions. It was supported by the provincial government but was defeated in the legislature.


Some provinces and territories amended their family law to extend statutory benefits to same-sex couples that were equivalent to those granted to unmarried cohabiting opposite-sex couples without establishing a specific name for the partnership. For example, Ontario was required to amend its family law legislation in 1999 in response to the  Supreme Court of Canada 's ruling in  M v H .


In 2007,  Colombia  came close to passing a law granting legal recognition to same-sex couples, but the bill failed on final passage in one house of the national legislature. However, a court decision in October 2007 extended social security and health insurance rights to same-sex couples. [ 128 ]  On January 29, 2009, the Constitutional Court ruled that cohabitating same-sex couples must be given all rights offered to unmarried heterosexual couples, [ 129 ]  making Colombia the first Latin American country to fully grant this right to all its citizens. Couples can claim these rights after living together for two years. Colombia has since approved same-sex marriage.


The  Legislative Assembly of Costa Rica  passed a bill in early July 2013 that "confers social rights and benefits of a civil union, free from discrimination", language inserted by lawmaker  José María Villalta Florez-Estrada  of the  Broad Front  party. After the bill passed, several media outlets reported that conservative lawmakers realized the bill's implications for same-sex unions and urged President  Laura Chinchilla , who is set to face Villalta in the 2014 presidential election, to use her  veto  power to stop the bill from becoming law. Chinchilla, who has suggested the courts should determine the legality of same-sex unions in Costa Rica, refused and signed the bill into law on 4 July. A gay couple has filed an appeal with the  Supreme Court of Justice of Costa Rica  asking that their union be recognized under the new law. [ 130 ]  Gay rights activists reacting to the law said it needs to survive a constitutional challenge in court. [ 131 ] [ 132 ]  Some constitutional lawyers stated that same-sex couples will "still lack legal capacity" to formalize their unions, despite passage of the bill. [ 133 ]


The  2008 Constitution of Ecuador  enacted civil unions between two people without regard to gender, giving same-sex couples the same rights as legally married heterosexual couples except for the right to adopt. [ 134 ]


In Europe:


In 2018, Minister of Justice Josef Moser announced that both marriage and registered partnership would be open to homosexuals and heterosexuals. This occurred because Helga Ratzenböck and Martin Seydl have been appealing for years [ timeframe? ]  in court for a registered civil partnership in Austria. At the  European Court of Human Rights  in Strasbourg they attempted to sue Austria for discrimination against their sexuality, [ when? ]  because they were a heterosexual couple and were excluded from the benefits of registered partnership, but this failed. [ 135 ] [ 136 ]  Only when the Constitutional Court of Austria opened up marriage to homosexuals in December 2018 registered partnerships also become possible for heterosexuals. After 35 years of living together, the two entered into a registered partnership in 2019. [ 137 ]


Civil unions were introduced in  Denmark  by law on 7 June 1989, the world's first such law, and came into effect on 1 October 1989. On 7 June 2012, the law was replaced by a new same-sex marriage law, which came into effect on 15 June 2012. [ 138 ]


Registered partnership was by civil ceremony only, but the  Church of Denmark  allowed priests to perform blessings of same-sex couples, as it stated that the church blesses people, not institutions. The new law makes same-sex marriages in churches possible, but allows vicars to decline marriages of same-sex couples in their church. [ 138 ]


On 17 March 2009, the  Folketing  introduced a bill that gave same-sex couples in registered partnerships the right to  adopt jointly . [ 139 ]  This bill was approved on 4 May 2010 and took effect on 1 July 2010. [ 140 ]


The  French  law providing benefits to same-sex couples also applies to opposite-sex couples who choose this form of partnership over marriage.  Known as the "Pacte civil de solidarité" (PACS), it is more easily dissolved than the divorce process applying to marriage.  Tax benefits accrue immediately (only from 2007 on [ citation needed ] ), while immigration benefits accrue only after the contract has been in effect for one year. The partners are required to have a common address, making it difficult for foreigners to use this law as a means to a residence permit, and difficult for French citizens to gain the right to live with a foreign partner – especially since the contract does not automatically give immigration rights, as marriage does. [ 141 ]


Between 2000 and 2010, the number of marriages decreased while the number of PACS strongly increased. In 2010, there were 3 PACS for every 4 marriages celebrated in France. [ 142 ]  Especially amongst heterosexual couples PACS is very popular, with 96 out of 100 PACS couples being heterosexual in the year 2019. [ 143 ]


Civil unions in  Germany  began in 2001. [ citation needed ]


In 2017, registered life partnership was replaced with marriage, with any couple regardless of sex allowed to marry. [ 144 ]


Greek parliament voted in favor of a Cohabitation Pact ( Greek : Σύμφωνο Συμβίωσης) giving almost the same rights as marriage to couples regardless of their sex. The draft was approved in the relevant Greek parliament committee [ when? ]  and during voting on 22 December 2015, the law was passed with 194 positive votes (out of 300). [ 145 ]


Civil unions in  Hungary  began in 2009. [ citation needed ]


Iceland  does not have a comprehensive legal act on civil unions ( Icelandic :  óvígð sambúð ). Instead, various laws deal with civil unions and their meaning. When Iceland legalised same-sex marriages in 2010, the Act on Registered Partnerships (87/1996) was abolished. Registered partnerships ( Icelandic :  staðfest samvist ) had been the principal legal unions for same-sex partners since the law was passed in 1996. [ 146 ]


In 2010, the lower house of the Irish Parliament  Dáil Éireann  passed the  bill on Civil Partnerships  unanimously. This bill allows civil partnerships of same-sex couples, and establishes an extensive package of rights, obligations and protections for same-sex couples who register as civil partners. [ 147 ]  The bill passed all stages of in both Houses of the Oireachtas, [ 148 ]  and came into effect on 1 January 2011.  The first partnership between two men was registered on 7 February 2011. [ 149 ]


Same-sex marriage has been  legal in Ireland  since 2015 following a  referendum . [ citation needed ]


Civil unions in  Italy  began in 2016. [ citation needed ]


Civil unions in  Liechtenstein  began in 2011. [ 150 ]


Civil unions in  Monaco  began in 2020. [ citation needed ]


Civil unions in  Montenegro  began in 2020. [ citation needed ]


In 2001, the  Netherlands  passed a law allowing same-sex couples to marry, in addition to its 1998 "registered partnership" law (civil union) for both same-sex and opposite-sex couples. [ 151 ] [ 152 ]


In 2004, Senator  Maria Szyszkowska  proposed a bill which would legalize same-sex civil unions in Poland. The project was approved by the  Senate  but was never voted upon by the  Sejm , as  Włodzimierz Cimoszewicz  (then the Marshal of the Sejm) did not bring it for the deliberation. [ This paragraph needs citation(s) ]


In 2008, when asked about same-sex civil unions,  First Cabinet of Donald Tusk  spokeswoman Agnieszka Liszka answered: " Council of Ministers  did not and would not take care of that matter." [ 153 ]


On January 25, 2013, Sejm voted upon three separate bills regarding same-sex civil unions in Poland: by the centre-left  Democratic Left Alliance , liberal  Palikot's Movement  and centre-right  Civic Platform . The first bill had 283 against, 137 for, 30 abstaining. The second had 276 against, 150 for, 23 abstaining. The third had 228 against, 211 for, 10 abstaining. All three were rejected, mainly with the votes of centre-right, right-wing and conservative parties:  Polish People's Party ,  Law and Justice  and  United Poland . A majority of deputies from the ruling centre-right  Civic Platform  also voted against the first two bills. [ 154 ] [ 155 ] [ 156 ]  The  Roman Catholic Church  in Poland,  Polish Orthodox Church  and  Polish Muslims  opposed all three bills.


In March 2013, Prime Minister Donald Tusk officially stated that a new project of civil unions bill would be presented to the parliament "in two months time" (in May 2013), but as of April 2014 [update] [ needs update ]  no such initiatives took place.


In a 2013 opinion poll conducted by  CBOS , 68% of Poles were against gays and lesbians publicly showing their way of life, 65% of Poles were against same-sex  civil unions , 72% were against same-sex marriage and 88% were against adoption by same-sex couples. [ 157 ]


In December 2014, the Sejm refused to deal with a civil partnership bill proposed by  Your Movement , with 235 MPs voting against debating the bill, and 185 MPs voting for. [ 158 ]


In May 2015, the Sejm again refused to deal with the topic, with 215 MPs voting against and only 146 for. The Prime Minister,  Ewa Kopacz , said that civil partnerships are an issue for the next parliament to deal with. [ 159 ]


The  Canton of Geneva  has a law on the cantonal level, the Partenariat cantonal (the Cantonal Domestic Partnership), since 2001. It grants  unmarried couples , whether same-sex or opposite-sex, many of the rights, responsibilities and protections that  married couples  have. However, it does not allow benefits in taxation, social security, or health insurance premiums (unlike the federal law). Geneva was the first Canton to recognise same-sex couples through this law.


On September 22, 2002, voters in the  Swiss  canton of  Zurich  voted to extend a number of marriage rights to same-sex partners, including tax, inheritance, and social security benefits. [ 160 ]  The law is limited to same-sex couples, and both partners must have lived in the canton for six months and formally commit to running a household together and supporting and aiding each another.


On November 12, 2003, the  Constituent assembly  of the  Canton of Fribourg  granted Registered Partnership as a constitutional right under the Article 14.


On January 27, 2004, the  Canton of Neuchâtel  voted for a law on the cantonal level, the Partenariat enregistré (the Cantonal Registered Partnership). It grants  unmarried couples , whether same-sex or opposite-sex, the same rights as married couple for cantonal matters such as responsibilities and protections, benefits in taxation, social security, or health insurance premiums.


On June 5, 2005, voters extended this right to the whole of Switzerland through a federal referendum. This was the first time that the civil union laws were affirmed in a nationwide referendum in any country. The Federal Domestic Partnership Law, reserved for same-sex couples, came into force on January 1, 2007. It grants the same rights as marriage, but full joint adoption rights, facilitated naturalization and medically assisted procreation are explicitly forbidden for same-sex domestic partners. [ 161 ]


In 2017, the Federal Councilor  Simonetta Sommaruga  addressed the issue that civil union is not open yet for heterosexual couples, in collaboration with experts at the University of Bern. In Geneva and Neuchâtel a type of civil union called cantonal PACS is available to opposite-sex and same-sex couples. [ 162 ]  The cantonal PACS effects are limited to cantonal law. The cantonal PACS, however, has no impact on civil status and inheritance, which are regulated by federal law. [ 163 ]


On September 26, 2021, the people of Switzerland approved on national referendum the initiative "Marriage for all", which would grant marriage and adoption rights for same-sex couples. This initiative would be made effective on July 1, 2022.


In 2003, the  British  government announced plans to introduce civil partnerships which would allow same-sex couples the rights and responsibilities resulting from marriage. The  Civil Partnership Bill  was introduced into the  House of Lords  on 30 March 2004. After considering amendments made by the  House of Commons , it was passed by the House of Lords, its final legislative hurdle, [ colloquialism ]  on 17 November 2004, and received  royal assent  on 18 November. The Act came into force on 5 December 2005, and same-sex, but not opposite-sex, couples were able to form the civil partnerships from 19 December 2005 in  Northern Ireland , 20 December 2005 in  Scotland  and 21 December 2005 in  England  and  Wales . [ 164 ]  Separate provisions were included in the first Finance Act 2005 to allow regulations to be made to amend tax laws to give the same tax advantages and disadvantages to couples in civil partnerships as apply to married couples. At that time, the  Church of England , the  state church  in England, permitted clergy to enter into same-sex civil partnerships. [ 165 ]


Aside from the manner in which couples register and the non-use of the word "marriage", civil partnerships grant most of the same legal rights as marriage and generally operate under the same constrictions (one difference being that marriage requires dissolution by divorce while a civil union does not). It is not legal to be in both a civil partnership and a marriage at the same time. Nevertheless, some of those in favour of legal same-sex marriage object that civil partnerships do not grant full equality.


Both same-sex marriages and civil unions of other nations will be automatically considered civil partnerships under UK law providing they came within Section 20 of the Act. This means, in some cases, non-Britons from nations with civil unions will have greater rights in the UK than in their native countries. For example, a Vermont civil union would have legal standing in the UK; however, in cases where one partner was American and the other British, the Vermont civil union would not provide the Briton with right of abode in Vermont (or any other US state or territory), whereas it would provide the American with right of abode in the UK.


In September 2011, the succeeding  coalition government  announced its intention to legalise same-sex marriage in England and Wales by 2015 at the latest. [ 166 ]  The future status of civil partnerships is unclear. The  Scottish Government , which has devolved responsibility for such legislation, held a consultation concerning both civil and religious same sex marriage in the autumn of 2011. [ when? ]  Legislation to allow same-sex marriage in England and Wales was passed by the Parliament of the United Kingdom in July 2013 and came into force on 13 March 2014, and the first same-sex marriages took place on 29 March 2014. The first same-sex marriages in Scotland took place in December 2014.


In June 2018, the Supreme Court ruled that restricting civil partnerships to same-sex couples was discriminatory. [ 167 ]  In response, the Prime Minister announced in October 2018 that civil partnerships would be opened to heterosexual couples. [ 168 ]  In autumn 2018 Theresa May announced that she would open up the "Civil Partnership" to heterosexual couples in England. [ 169 ]  As of 31st December 2019 it is possible for both same-sex and heterosexual couples to enter into a civil partnership in England. [ 170 ]


On 9 November 2006,  Mexico City 's  unicameral   Legislative Assembly  passed and approved (43–17) a bill legalizing  same-sex civil unions , under the name  Ley de Sociedades de Convivencia  (Law for Co-existence Partnerships), which became effective on 16 March 2007. [ 171 ]  The law gives  property  and  inheritance  rights to same-sex couples. On 11 January 2007, the northern state of  Coahuila , which borders Texas, passed a similar bill (20–13), under the name  Pacto Civil de Solidaridad  (Civil Pact of Solidarity). [ 172 ]  Unlike Mexico City's law, once same-sex couples have registered in Coahuila, the state protects their rights no matter where they live in the country. [ 172 ]  Twenty days after the law had passed, [ when? ]  the country's first same-sex civil union took place in  Saltillo, Coahuila . [ 173 ]  Civil unions have been proposed in at least six states since 2006. [ 174 ]


In  Colima ,  governor   Mario Anguiano Moreno  has agreed to discuss the legalization of civil unions and adoption by same-sex couples. [ 175 ] [ when? ]  In  Jalisco , local congress approved on 31 October 2013 the Free Coexistence Act, which allows the performance of civil unions in the state. [ 176 ]


On 9 December 2004 the  New Zealand   Parliament  passed the Civil Union Bill, establishing civil unions for same-sex and opposite-sex couples. The debate over Civil Unions was highly divisive in New Zealand, inspiring great public emotion both for and against the passing. A companion bill, the Relationships (Statutory References) Bill was passed shortly thereafter to remove discriminatory provisions on the basis of relationship status from a range of statutes and regulations. As a result of these bills, all couples in New Zealand, whether married, in a civil union, or in a de facto partnership, now generally enjoy the same rights and undertake the same obligations. These rights extend to immigration, next-of-kin status, social welfare, matrimonial property and other areas.


The  Civil Union Act 2004  came into effect on 26 April 2005 with the first unions able to occur from Friday 29 April 2005.


In  South Africa , a "civil union" is either a marriage or a civil partnership, although the term "civil union" is commonly used when "civil partnership" is meant. Same-sex and opposite-sex couples may register their unions either as  marriages  or as civil partnerships. In laws where "marriage" is mentioned, its definition now retroactively includes civil partnerships. [ This paragraph needs citation(s) ]


The first civil unions in the United States were offered by the state of  Vermont  in 2000. The  federal government  does not recognize these unions. By the end of 2006,  Connecticut  and New Jersey had also enacted civil union laws;  New Hampshire  followed in 2007. Furthermore, California's domestic partnership law had been expanded to the point that it became practically a civil union law as well. The same might be said [ by whom? ]  for domestic partnership in the District of Columbia, domestic partnership in Washington, and domestic partnership in Oregon.


Jurisdictions in the U.S. that offer civil unions or domestic partnerships granting nearly all of the state-recognized rights of marriage to same-sex couples include:


States in the U.S. with domestic partnerships or similar status granting some of the rights of marriage include:


Since October 2014, all states that provide for civil unions, domestic partnerships, or similar arrangements between same-sex partners also allow same-sex partners to legally wed.


In 2013,  Bisbee  became the first city in Arizona to legalize civil unions for same-sex couples. [ 177 ]  After its passage, the state's Attorney General,  Tom Horne , threatened to challenge the law in court, arguing that it violated the state's constitution. [ 178 ]  However, the Attorney General agreed to withdraw the challenge after Bisbee amended the law, and the civil union ordinance was approved. [ 179 ]


Following Bisbee, also in 2013,  Tucson  became the second municipality to legalize civil unions. [ 180 ]   Jerome  followed in the same year. [ 181 ]  Also in 2013,  Clarkdale  and  Cottonwood  were the next cities in the Verde Valley to pass civil unions. [ 182 ] [ 183 ]  A measure to allow civil unions failed in  Camp Verde  by a split 3–3 vote in the city council making it the only city in the Verde Valley to not have passed the bill. [ 184 ]


Sedona  passed civil unions in September 2013. [ 185 ]  The city of  Tempe  considered legal advice about a civil union ordinance, but it did not pass a bill. [ 186 ]  After the legalization of same-sex marriage in Arizona, civil unions may continue to be registered in the cities that had legalized the ordinances. [ 187 ]


In California, where domestic partnership (DP) has been available to same-sex and certain opposite-sex couples since 2000, a wholesale revision of the law in 2005 made it substantially equivalent to marriage at the state level.  In 2007, the Legislature took a further step when it required same-sex DP couples to file state income taxes jointly.  (Couples must continue to file federal taxes as individuals.)  In the May 2008  In re Marriage Cases  decision, the state supreme court noted nine  differences between Domestic Partnerships and same-sex marriage  in state law, including a cohabitation requirement for domestic partners, access to CalPERS long-term care insurance (but not CalPERS in general), and the lack of an equivalent to California's "confidential marriage" institution. [ 7 ]  The cohabitation requirement was dropped on January 1, 2012, and a "confidential option" for domestic partners became available the same day.


A bill to establish civil unions for same-sex and opposite-sex couples passed both chambers of the Colorado legislature and was signed into law by Governor  John Hickenlooper . Civil unions began on May 1, 2013.


In 2005, the  Connecticut General Assembly  passed a bill to adopt civil unions in Connecticut.  Connecticut's civil unions were identical to marriage and provided all of the same rights and responsibilities except for the title. Connecticut was the first state in the U.S. to voluntarily pass a same-sex civil unions law through the legislature without any immediate court intervention. [ 188 ]  The law was repealed on October 1, 2010, and replaced with a law making marriage gender-neutral.


Delaware Governor  Jack Markell  signed a civil union bill on May 12, 2011, that establishes civil unions in the state effective January 1, 2012. [ 189 ]  The law was repealed on July 1, 2014, and replaced with a law making marriage gender-neutral.


Same-sex marriage in the District of Columbia was legalized on December 18, 2009.  Marriage licenses became available on March 3, 2010, and marriages began on March 9, 2010.  Domestic Partnerships in the District of Columbia  (1992 law implemented, 2002 law came into effect – expanded over time to 2009)


Hawaii legalized civil unions for same-sex and opposite-sex couples on January 1, 2012. Same-sex marriage became legal on December 2, 2013.


On December 1, 2010, the Illinois state senate passed SB1716 – the "Illinois Religious Freedom Protection and Civil Union Act" – in a 32–24–1 vote, just one day after the Illinois House of Representatives did the same in a 61–52–2 vote. On January 31, 2011, Illinois state Governor Pat Quinn signed SB1716 into law, establishing civil unions for same-sex and opposite-sex couples. The new law came into effect on June 1, 2011.  The provision allowing opposite-sex couples to establish a civil union effectively doubles as a tool for widowed seniors to keep  survivor's benefits  from a marriage while gaining marital rights at the state level with another partner. [ 190 ]


Maine legalized domestic partnership for same-sex and opposite-sex couples in 2004. Maine's domestic partnership registry only provides limited rights, most of which are geared toward [ colloquialism ]  protecting couples' security in emergency situations.


On April 26, 2007, the  New Hampshire General Court  (state legislature) passed a civil union bill, and Governor  John Lynch  signed the bill into law on May 31, 2007. [ 191 ]  At the time, New Hampshire was "... the first state to embrace same-sex unions without a court order or the threat of one". [ 192 ]  The New Hampshire civil union legislation became effective on January 1, 2008. [ 193 ]  The law was replaced by the same-sex marriage law on January 1, 2010.


On October 25, 2006, the  Supreme Court of New Jersey  gave  New Jersey lawmakers  180 days to rewrite the state's marriage laws, either including same-sex couples or creating a new system of  civil unions  for them. On December 14 the Legislature passed a bill establishing  civil unions in New Jersey , which was signed into law by  Governor   Jon Corzine  on December 21, 2006.  The first civil unions took place on February 19, 2007. [ 194 ]


There are differences between civil unions and domestic partnerships.  In 2004, the state of  New Jersey  enacted a domestic partnership law, offering certain limited rights and benefits to same-sex and different-sex couples.  In 2006, however, after a  state Supreme Court   ruling  that same-sex couples must be extended all the rights and benefits of marriage, the Legislature passed a civil unions law, effective in 2007, which is an attempt to satisfy the court's ruling.


On May 31, 2009, the Nevada legislature overrode Governor  Jim Gibbons ' veto of a domestic partnership bill. The bill allows registered domestic partners, whether they are a same-sex or opposite-sex couple, to have most of the state level rights and responsibilities afforded to married couples. It does not require any other entity to provide rights or benefits afforded to married individuals. This has left the partnership bill ineffective compared to those of other states. The law took effect on 1 October 2009.


Since 4 February 2008, Oregon offers domestic partnerships which grant nearly all of the state-recognized rights of marriage to same-sex couples.


Civil unions were permitted in Rhode Island since July 1, 2011 until July 1, 2013.


The civil unions law [ 195 ]  that was passed in the  Vermont General Assembly  in 2000 was a response to the  Vermont Supreme Court  ruling in  Baker v. Vermont , requiring that the state grant same-sex couples the same rights and privileges accorded to married couples under the law.


A Vermont civil union is nearly identical to a legal marriage, as far as the rights and responsibilities for which state law, not federal law, is responsible are concerned. [ 195 ]  It grants partners  next-of-kin  rights and other protections that heterosexual married couples also receive.  However, despite the  "full faith and credit" clause  of the  United States Constitution , civil unions are generally not recognized outside Vermont in the absence of specific legislation.  Opponents of the law have supported the  Defense of Marriage Act  and the proposed  Federal Marriage Amendment  in order to prevent obligatory recognition of same-sex couples in other jurisdictions.  This means that many of the advantages of marriage, which fall in the federal jurisdiction (over 1,100 federal laws, such as joint federal income tax returns, visas and work permits for the foreign partner of a U.S. citizen, etc.), are not extended to the partners of a Vermont civil union.


Regarding voluntary recognition of the civil union in other jurisdictions,  New York City 's Domestic Partnership Law, passed in 2002, recognizes civil unions formalized in other jurisdictions.  Germany 's international civil law (EGBGB) also accords to Vermont civil unions the same benefits and responsibilities that apply in Vermont, as long as they do not exceed the standard accorded by German law to a German civil union. The law was replaced by the same-sex marriage law on September 1, 2009.


Washington offers domestic partnerships which grant nearly all of the state-recognized rights of marriage to same-sex couples. Washington is the first state to have passed a same-sex civil union bill by a popular vote.


Washington legalized same-sex marriage early in 2012, which provided that a couple in a civil union would have two years to convert their civil union to a marriage. The law was upheld by popular  referendum  in November 2012. [ 196 ]


Civil unions in Uruguay were allowed nationwide from January 1, 2008.


To date, only two countries, Spain and Portugal, have signed onto the  Convention on the Recognition of Registered Partnerships , a draft multilateral agreement on the status of civil, unmarried partnerships. The document is inclusive of rights for both same and opposite sex partnerships.


In  biology , a  cline  is a measurable  gradient  in a single characteristic (or biological trait) of a species across its  geographical range . [ 1 ]  Clines usually have a genetic (e.g.  allele frequency ,  blood type ), or phenotypic (e.g. body size, skin pigmentation) character. They can show either smooth, continuous gradation in a character, or more abrupt changes in the trait from one geographic region to the next. [ 2 ]


A cline is a spatial gradient in a single specific trait, rather than in a collection of traits; [ 3 ]  a single population can therefore have as many clines as it has traits, at least in principle. [ 4 ]  Additionally, as  Julian Huxley  recognised, these multiple independent clines may not act in concordance with each other. For example, it has been observed that in Australia, birds generally become smaller the further towards the north of the country they are found. In contrast, the intensity of their plumage colouration follows a different geographical trajectory, being most vibrant where humidity is highest and becoming less vibrant further into the arid centre of the country. [ 5 ]
Because of this, Huxley described the notion of clines as an "auxiliary taxonomic principle,” meaning that clinal variation in a species is not awarded taxonomic recognition in the way  subspecies  or  species  are. [ 1 ]


The term  cline  was coined by Huxley in 1938 from the  Greek  κλίνειν  klinein , meaning "to lean.” While it and the term  ecotype  are sometimes used interchangeably, they do in fact differ in that  ecotype  refers to a population which differs from other populations in a number of characters, rather than the single character that varies amongst populations in a cline. [ 4 ]


Clines are often cited to be the result of two opposing drivers:  selection  and  gene flow  (also known as migration). [ 5 ]  Selection causes  adaptation  to the local environment, resulting in different genotypes or phenotypes being favoured in different environments. This diversifying force is countered by gene flow, which has a homogenising effect on populations and prevents  speciation  through causing  genetic admixture  and blurring any distinct genetic boundaries. [ 5 ]


Clines are generally thought to arise under one of two conditions: "primary differentiation" (also known as "primary contact" or "primary intergradation"), or "secondary contact" (also known as "secondary introgression", or "secondary intergradation"). [ 2 ] [ 6 ] [ 7 ]


Clines produced through this way are generated by spatial heterogeneity in environmental conditions. The mechanism of selection acting upon organisms is therefore external. Species ranges frequently span environmental gradients (e.g. humidity, rainfall, temperature, or day length) and, according to natural selection, different environments will favour different  genotypes  or  phenotypes . [ 8 ]  In this way, when previously genetically or phenotypically uniform populations spread into novel environments, they will evolve to be uniquely adapted to the local environment, in the process potentially creating a gradient in a genotypic or phenotypic trait.


Such clines in characters can not be maintained through selection alone if much gene flow occurred between populations, as this would tend to swamp out the effects of local adaptation. However, because species usually tend to have a limited dispersal range (e.g. in an  isolation by distance  model), restricted gene flow can serve as a type of barrier which encourages geographic differentiation. [ 9 ]  However, some degree of migration is often required to maintain a cline; without it,  speciation  is likely to eventually occur, as local adaptation can cause reproductive isolation between populations. [ 2 ]


A classic example of the role of environmental gradients in creating clines is that of the peppered moth,  Biston betularia , in the UK. During the 19th century, when the industrial sector gained traction, coal emissions blackened vegetation across northwest England and parts of northern Wales. As a result of this, lighter  morphs  of the moth were more visible to predators against the blackened tree trunks and were therefore more heavily predated relative to the darker morphs. Consequently, the frequency of the more  cryptic  melanic morph of the peppered moth increased drastically in northern England. This cline in morph colour, from a dominance of lighter morphs in the west of England (which did not suffer as heavily from pollution), to the higher frequency of melanic forms in the north, has slowly been degrading since limitations to sooty emissions were introduced in the 1960s. [ 10 ]


Clines generated through this mechanism have arisen through the joining of two formerly isolated populations which differentiated in  allopatry , creating an intermediate zone. This secondary contact scenario may occur, for example, when climatic conditions change, allowing the ranges of populations to expand and meet. [ 6 ]  Because over time the effect of gene flow will tend to eventually swamp out any regional differences and cause one large homogenous population, for a stable cline to be maintained when two populations join there must usually be a selective pressure maintaining a degree of differentiation between the two populations. [ 2 ]


The mechanism of selection maintaining the clines in this scenario is often intrinsic. This means that the fitness of individuals is independent of the external environment, and selection is instead dependent on the genome of the individual. Intrinsic, or endogenous, selection can give rise to clines in characters through a variety of mechanisms. One way it may act is through  heterozygote disadvantage , in which intermediate genotypes have a lower relative fitness than either homozygote genotypes. Because of this disadvantage, one allele will tend to become fixed in a given population, such that populations will consist largely of either  AA  ( homozygous  dominant) or  aa  (homozygous recessive) individuals. [ 11 ]  The cline of hetero zygotes  that is created when these respective populations come into contact is then shaped by the opposing forces of selection and gene flow; even if selection against heterozygotes is great, if there is some degree of gene flow between the two populations, then a steep cline may be able to be maintained. [ 12 ] [ 13 ]
Because instrinsic selection is independent of the external environment, clines generated by selection against hybrids are not fixed to any given geographical area and can move around the geographic landscape. [ 14 ]  Such  hybrid zones  where hybrids are a disadvantage relative to their parental lines (but which are nonetheless maintained through selection being counteracted by gene flow) are known as "tension zones". [ 11 ]


Another way in which selection can generate clines is through  frequency-dependent selection . Characters that could be maintained by such frequency-dependent selective pressures include warning signals ( aposematism ). For example, aposematic signals in  Heliconius  butterflies sometimes display steep clines between populations, which are maintained through  positive frequency dependence . [ 13 ]  This is because heterozygosity,  mutations  and  recombination  can all produce patterns that deviate from those well-established signals which mark prey as being unpalatable. These individuals are then predated more heavily relative to their counterparts with "normal" markings (i.e. selected against), creating populations dominated by a particular pattern of warning signal. As with heterozygote disadvantage, when these populations join, a narrow cline of intermediate individuals could be produced, maintained by gene flow counteracting selection. [ 13 ] [ 15 ]


Secondary contact could lead to a cline with a steep gradient if heterozygote disadvantage or frequency-dependent selection exists, as intermediates are heavily selected against. Alternatively, steep clines could exist because the populations have only recently established secondary contact, and the character in the original allopatric populations had a large degree of differentiation. As genetic admixture between the population increases with time however, the steepness of the cline is likely to decrease as the difference in character is eroded. However, if the character in the original allopatric populations was not very differentiated to begin with, the cline between the populations need not display a very steep gradient. [ 2 ]  Because both primary differentiation and secondary contact can therefore give rise to similar or identical clinal patterns (e.g. gently sloping clines), distinguishing which of these two processes is responsible for generating a cline is difficult and often impossible. [ 2 ]  However, in some circumstances a cline and a geographic variable (such as humidity) may be very tightly linked, with a change in one corresponding closely to a change in the other. In such cases it may be tentatively concluded that the cline is generated by primary differentiation and therefore moulded by environmental selective pressures. [ 7 ]


While selection can therefore clearly play a key role in creating clines, it is theoretically feasible that they might be generated by  genetic drift  alone. It is unlikely that large-scale clines in genotype or phenotype frequency will be produced solely by drift. However, across smaller geographical scales and in smaller populations, drift could produce temporary clines. [ 16 ]  The fact that drift is a weak force upholding the cline however means that clines produced this way are often random (i.e. uncorrelated with environmental variables) and subject to breakdown or reversal over time. [ 2 ]  Such clines are therefore unstable and sometimes called "transient clines". [ 17 ]


The steepness, or gradient, of a cline reflects the extent of the differentiation in the character across a geographic range. [ 2 ]  For example, a steep cline could indicate large variation in the colour of plumage between adjacent bird populations. It has been previously outlined that such steep clines may be the result of two previously allopatric populations with a large degree of difference in the trait having only recently established gene flow, or where there is strong selection against hybrids. However, it may also reflect a sudden environmental change or boundary. Examples of rapidly changing environmental boundaries like this include abrupt changes in the heavy metal content of soils, and the consequent narrow clines produced between populations of  Agrostis  that are either adapted to these soils with high metal content, or adapted to "normal" soil. [ 2 ] [ 18 ]
Conversely, a shallow cline indicates little geographical variation in the character or trait across a given geographical distance. This may have arisen through weak differential environmental selective pressure, or where two populations established secondary contact a long time ago and gene flow has eroded the large character differentiation between the populations.


The gradient of a cline is related to another commonly referred to property, clinal width. A cline with a steep slope is said to have a small, or narrow, width, while shallower clines have larger widths. [ 7 ]


According to Huxley, clines can be classified into two categories; continuous clines and discontinuous stepped clines. [ 1 ]  These types of clines characterise the way that a genetic or phenotypic trait transforms from one end of its geographical range of the species to the other.


In continuous clines, all populations of the species are able to interbreed and there is gene flow throughout the entire range of the species. In this way, these clines are both biologically (no clear subgroups) and geographically (contiguous distribution) continuous.
Continuous clines can be further sub-divided into smooth and stepped clines.


Unlike in continuous clines, in discontinuous clines the populations of species are allopatric, meaning there is very little or no gene flow amongst populations. The genetic or phenotypic trait in question always shows a steeper gradient between groups than within groups, as in continuous clines. Discontinuous clines follow the same principles as continuous clines by displaying either


It was originally assumed that geographic isolation was a necessary precursor to speciation ( allopatric speciation ). [ 6 ]  The possibility that clines may be a precursor to speciation was therefore ignored, as they were assumed to be evidence of the fact that in contiguous populations gene flow was too strong a force of homogenisation, and selection too weak a force of differentiation, for speciation to take place. [ 2 ]  However, the existence of particular types of clines, such as  ring species , in which populations did not differentiate in allopatry but the terminal ends of the cline nonetheless do not interbreed, cast into doubt whether complete geographical isolation of populations is an absolute requirement for speciation.


Because clines can exist in populations connected by some degree of gene flow, the generation of new species from a previously clinal population is termed  parapatric speciation . Both extrinsic and intrinsic selection can serve to generate varying degrees of  reproductive isolation  and thereby instigate the process of  speciation . For example, through environmental selection acting on populations and favouring particular allele frequencies, large genetic differences between populations may accumulate (this would be reflected in clinal structure by the presence of numerous very steep clines). If the local genetic differences are great enough, it may lead unfavourable combinations of genotypes and therefore to hybrids being at a decreased fitness relative to the parental lines. When this hybrid disadvantage is great enough, natural selection will select for  pre-zygotic  traits in the homozygous parental lines that reduce the likelihood of disadvantageous hybridisation - in other words, natural selection will favour traits that promote assortative mating in the parental lines. [ 14 ]  This is known as  reinforcement  and plays an important role in parapatric and  sympatric speciation . [ 20 ] [ 2 ]


Clines can be portrayed graphically on maps using lines that show the transition in character state from one end of the geographic range to the other. Character states can however additionally be represented using isophenes, defined by Ernst Mayr as "lines of equal expression of a clinally varying character". [ 5 ]  In other words, areas on maps that demonstrate the same biological phenomenon or character will be connected by something that resembles a contour line. When mapping clines therefore, which follow a character gradation from one extreme to the other, isophenes will transect clinal lines at a right angle.


Although the term "cline" was first officially coined by Huxley in 1938, gradients and geographic variations in the character states of species have been observed for centuries. Indeed, some gradations have been considered so ubiquitous that they have been labelled  ecological "rules" . One commonly cited example of a gradient in morphology is  Gloger's Rule , named after  Constantin Gloger , who observed in 1833 that environmental factors and the pigmentation of avian  plumage  tend to covary with each other, such that birds found in arid areas near the Equator tend to be much darker than those in less arid areas closer to the Poles.  Since then, this rule has been extended to include many other animals, including flies, butterflies, and wolves. [ 21 ]


Other ecogeographical rules include  Bergmann's Rule , coined by  Carl Bergmann  in 1857, which states that  homeotherms  closer to the Equator tend to be smaller than their more northerly or southerly conspecifics. [ 22 ]  One of the proposed reasons for this cline is that larger animals have a relatively smaller surface area to volume ratio and therefore improved heat conservancy – an important advantage in cold climates. [ 22 ]  The role of the environment in imposing a selective pressure and producing this cline has been heavily implicated due to the fact that Bergmann's Rule has been observed across many independent lineages of species and continents. For example, the  house sparrow , which was introduced in the early 1850s to the eastern United States, evolved a north-south gradient in size soon after its introduction. This gradient reflects the gradient that already existed in the house sparrow's native range in Europe. [ 23 ]


Ring species [ 24 ]  are a distinct type of cline where the geographical distribution in question is circular in shape, so that the two ends of the cline overlap with one another, giving two adjacent populations that rarely  interbreed  due to the cumulative effect of the many changes in phenotype along the cline. The populations elsewhere along the cline interbreed with their geographically adjacent populations as in a standard cline. In the case of  Larus  gulls, the habitats of the end populations even overlap, which introduces questions as to what constitutes a species: nowhere along the cline can a line be drawn between the populations, but they are unable to interbreed.


In humans, clines in the frequency of blood types has allowed scientists to infer past population migrations. For example, the Type B blood group reaches its highest frequency in Asia, but become less frequent further west. From this, it has been possible to infer that some Asian populations migrated towards Europe around 2,000 years ago, causing genetic admixture in an  isolation by distance  model. In contrast to this cline, blood Type A shows the reverse pattern, reaching its highest frequency in Europe and declining in frequency towards Asia. [ 25 ]


The  coefficient of inbreeding  ( COI ) is a number measuring how  inbred  an individual is. Specifically, it is the  probability  that two  alleles  at any  locus  in an individual are identical by descent from a  common ancestor  of the two parents. [ 1 ] [ 2 ] [ 3 ] [ 4 ]  A higher COI will make the traits of the offspring more predictable, but also increases the risk of health issues. In dog breeding, it is recommended to keep the COI less than 5%; however, in some breeds this may not be possible without  outcrossing .  [ 5 ]


An individual is said to be inbred if there is a loop in its  pedigree chart . A loop is defined as a path that runs from an individual up to the  common ancestor  through one parent and back down to the other parent, without going through any individual twice. The number of loops is always the number of common ancestors the parents have. If an individual is inbred, the coefficient of inbreeding is calculated by summing all the probabilities that an individual receives the same allele from its father's side and mother's side. As every individual has a 50% chance of passing on an allele to the next generation, the formula depends on 0.5 raised to the power of however many generations separate the individual from the common ancestor of its parents, on both the father's side and mother's side. This number of generations can be calculated by counting how many individuals lie in the loop defined earlier. Thus, the coefficient of inbreeding (f) of an individual X can be calculated with the following formula: [ 6 ] [ 1 ]


f

 X

 =
 ∑

 0.5

 n
 −
 1

 ⋅
 (
 1
 +

 f

 A

 )

 {\displaystyle f_{X}=\sum 0.5^{n-1}\cdot (1+f_{A})}

where

 n

 {\displaystyle n}

  is the number of individuals in the aforementioned loop, and

 f

 A

 {\displaystyle f_{A}}

  is the coefficient of inbreeding of the common ancestor of X's parents.


To give an example, consider the following pedigree.


In this pedigree chart, G is the progeny of C and F, and C is the biological  uncle  of F. To find the coefficient of inbreeding of G, first locate a loop that leads from G to the  common ancestor  through one parent and back down to the other parent without going through the same individual twice. There are only two such loops in this chart, as there are only 2 common ancestors of C and F. The loops are G - C - A - D - F and G - C - B - D - F, both of which have 5 members.


Because the common ancestors of the parents (A and B) are not inbred themselves,

 f

 A

 =
 0

 {\displaystyle f_{A}=0}

 . Therefore the coefficient of inbreeding of individual G is

 f

 G

 =
 ∑

 0.5

 5
 −
 1

 ⋅
 (
 1
 +
 0
 )
 =

 0.5

 4

 +

 0.5

 4

 =
 12.5
 %

 {\displaystyle f_{G}=\sum 0.5^{5-1}\cdot (1+0)=0.5^{4}+0.5^{4}=12.5\%}

 .


If the parents of an individual are not inbred themselves, the coefficient of inbreeding of the individual is one-half the  coefficient of relationship  between the parents. This can be verified in the previous example, as 12.5% is one-half of 25%, the coefficient of relationship between an uncle and a niece.


^A  At this point the individuals are considered to be part of an  inbred strain , and each individual can effectively be considered to be  clones .


The  coefficient of relationship  is a measure of the degree of  consanguinity  (or biological relationship) 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 general, the higher the level of inbreeding the closer the coefficient of relationship between the parents approaches a value of 1, expressed as a percentage, [ a ]  and approaches a value of 0 for individuals with arbitrarily remote common ancestors.


The coefficient of relationship (

 r

 {\displaystyle r}

 ) between two individuals B and C is obtained by a summation of coefficients calculated for every line by which they are connected to their  common ancestors . Each such line connects the two individuals via a common ancestor, passing through no individual which is not a common ancestor more than once. A path coefficient between an ancestor A and an offspring O separated by

 n

 {\displaystyle n}

  generations is given as:


where

 f

 A

 {\displaystyle f_{A}}

  and

 f

 O

 {\displaystyle f_{O}}

  are the  coefficients of inbreeding  for A and O, respectively.


The coefficient of relationship

 r

 B
 C

 {\displaystyle r_{BC}}

  is now obtained by summing over all path coefficients:


By assuming that the pedigree can be traced back to a sufficiently remote population of perfectly random-bred stock ( f A  = 0 for all  A  in the sum) the definition of  r  may be simplified to


where  p  enumerates all paths connecting B and C with unique common ancestors (i.e. all paths terminate at a common ancestor and may not pass through a common ancestor to a common ancestor's ancestor), and  L(p)  is the length of the path  p .


To give an (artificial) example:
Assuming that two individuals share the same 32 ancestors of  n  = 5 generations ago, but do not have any common ancestors at four or fewer generations ago, their coefficient of relationship would be


Individuals for which the same situation applies for their 1024 ancestors of ten generations ago would have a coefficient of  r  =  2 −10  = 0.1%.
If follows that the value of  r  can be given to an accuracy of a few percent if the family tree of both individuals is known for a depth of five generations, and to an accuracy of a tenth of a percent if the known depth is at least ten generations. The contribution to  r  from common ancestors of 20 generations ago (corresponding to roughly 500 years in human genealogy, or the contribution from common descent from a  medieval  population) falls below one  part-per-million .


The coefficient of relationship is sometimes used to express  degrees of kinship  in numeric terms in human  genealogy .


In human relationships, the value of the coefficient of relationship is usually calculated based on the knowledge of a full family tree extending to a comparatively small number of generations, perhaps of the order of three or four. As explained above, the value for the coefficient of relationship so calculated is thus a lower bound, with an actual value that may be up to a few percent higher. The value is accurate to within 1% if the full family tree of both individuals is known to a depth of seven generations. [ c ]


A first-degree relative (FDR) is a person's  parent  (father or mother),  sibling  (brother or sister) or  child  (son or daughter). [ 1 ]  It constitutes a category of family members that largely overlaps with the term  nuclear family , but without spouses. [ 2 ]  If the persons are  related by blood , the first degree relatives share approximately 50% of their genes. First-degree relatives are a common measure used to diagnose risks for common diseases by analyzing family history. [ 3 ]


A second-degree relative (SDR) is someone who shares 25% of a person's genes. It includes  uncles ,  aunts ,  nephews ,  nieces ,  grandparents ,  grandchildren ,  half-siblings  and double-first cousins. [ 4 ] [ 5 ] [ 6 ]


Third-degree relatives are a segment of the  extended family  and includes first cousins, great-grandparents and great-grandchildren. [ 7 ]  Third-degree relatives are generally defined by the expected amount of genetic overlap that exists between two people, with the third-degree relatives of an individual sharing approximately 12.5% of their genes. [ 8 ]  The category includes great-grandparents, great-grandchildren, granduncles,  grandaunts, grandnephews, grandnieces, first cousins, [ 9 ]  half-uncles, half-aunts, half-nieces and half-nephews.


Most  incest laws  concern the relationships where  r  = 25% or higher, although many ignore the rare case of double first cousins. Some jurisdictions also prohibit sexual relations or marriage  between cousins  of various degree, or individuals related only through  adoption  or  affinity . Whether there is any likelihood of conception is generally considered irrelevant.


The  kinship coefficient  is a simple measure of relatedness, defined as the  probability  that a pair of randomly sampled homologous  alleles  are  identical by descent . [ 12 ]  More simply, it is the probability that an allele selected randomly from an individual, i, and an allele selected at the same  autosomal  locus from another individual, j, are identical and from the same ancestor.


The coefficient of relatedness is equal to twice the kinship coefficient. [ 13 ]


The kinship coefficient between two individuals, i and j, is represented as Φ ij . The kinship coefficient between a non-inbred individual and itself, Φ ii , is equal to 1/2. This is due to the fact that humans are  diploid , meaning the only way for the randomly chosen alleles to be identical by descent is if the same allele is chosen twice (probability 1/2). Similarly, the relationship between a parent and a child is found by the chance that the randomly picked allele in the child is from the parent (probability 1/2) and the probability of the allele that is picked from the parent being the same one passed to the child (probability 1/2). Since these two events are independent of each other, they are multiplied Φ ij  = 1/2 X 1/2 = 1/4. [ 14 ] [ 15 ]


Cognatic kinship  is a mode of  descent  calculated from an  ancestor  counted through any combination of male and female links, or a system of  bilateral kinship  where relations are traced through both a father and mother. [ 1 ]  Such relatives may be known as  cognates .


Collateral  is a term used in  kinship  to describe kin, or lines of kin, that are not in a direct line of descent from an individual. [ 1 ]  Examples of collateral relatives include siblings of parents or grandparents and their descendants (uncles, aunts, and cousins). [ 2 ]  Collateral descent is contrasted with  lineal descent : those related directly by a line of descent such as the children, grandchildren, great-grandchildren, etc. of an individual. Though both forms are  consanguineal  (blood relations), collaterals are neither ancestors nor descendants of a given person. [ 3 ]  In legal terminology, 'Collateral descendant' refers to relatives descended from a sibling of an ancestor, and thus a niece, nephew, or cousin. [ 4 ]


Consanguinity  (from  Latin   consanguinitas  'blood relationship') is the characteristic of having a  kinship  with a relative who is descended from a common ancestor.


Many jurisdictions have laws prohibiting people who are closely related by blood from  marrying  or having sexual relations with each other. The  degree of consanguinity  that gives rise to this prohibition varies from place to place. [ 2 ]  On the other hand, around 20% of the global population lives in areas where some consanguinous marriages are preferred. [ 3 ]  The degree of relationships are also used to determine  heirs  of an estate according to statutes that govern  intestate  succession, which also vary from jurisdiction to jurisdiction. [ 4 ]  In some communities and time periods,  cousin marriage  is allowed or even encouraged; in others, it is  taboo , and considered to be  incest .


The degree of relative consanguinity can be illustrated with a  consanguinity table  in which each level of lineal consanguinity ( generation  or  meiosis ) appears as a row, and individuals with a collaterally consanguineous relationship share the same row. [ 5 ]  The Knot System is a numerical notation that describes consanguinity using the  Ahnentafel  numbers of shared ancestors. [ 6 ]


The degree of kinship between two people may give rise to several legal issues. Some laws prohibit  sexual relations  between closely related people, referred to as  incestuous . Laws may also bar marriage between closely related people, which are almost universally prohibited to the second degree of consanguinity. [ citation needed ]  Some jurisdictions forbid marriage between  first cousins , while others do not. Marriage with aunts and uncles ( avunculate marriage ) is legal in several countries. [ 7 ] [ 8 ]


Consanguinity is also relevant to inheritance, particularly with regard to  intestate succession . In general, laws tend to favor inheritance by persons closely related to the deceased. Some jurisdictions ban citizens from service on a jury on the basis of consanguinity as well as affinity with persons involved in the case. [ 9 ]  In many countries, laws prohibiting  nepotism  ban employment of, or certain kinds of contracts with, the near relations of public officers or employees. [ citation needed ]


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Under  Roman civil law , which the early  canon law of the Catholic Church  followed, couples were forbidden to marry if they were within four degrees of consanguinity. [ 10 ]  Around the ninth century the church raised the number of prohibited degrees to seven and changed the method by which they were calculated; instead of the former Roman practice of counting each generational link up to the common ancestor and then down again to the proposed spouse, the new method computed consanguinity only by counting back the number of generations to the common ancestor. [ 10 ]  Intermarriage was now prohibited to anyone more closely related than seventh cousins, which meant that in particular the nobility struggled to find partners to marry, the pool of non-related prospective spouses having become substantially smaller. They had to either defy the church's position or look elsewhere for eligible marriage candidates. [ 10 ]  In the  Roman Catholic Church , unknowingly marrying a closely consanguineous blood relative was grounds for a  declaration of nullity , but during the eleventh and twelfth centuries  dispensations  were granted with increasing frequency due to the thousands of persons encompassed in the prohibition at seven degrees and the hardships this posed for finding potential spouses. [ 11 ]


In 1215, the  Fourth Lateran Council  made what they believed was a necessary change to canon law reducing the number of prohibited degrees of consanguinity from seven back to four, but retaining the later method of calculating degrees. [ 12 ] [ 13 ]  After 1215, the general rule was that fourth cousins could marry without dispensation, greatly reducing the need for dispensations. [ 11 ]  In fourteenth century England, for example, papal dispensations for annulments due to consanguinity (and  affinity ) were relatively few. [ 14 ]


The ban on marriage to minor degrees of relationship imposed by the Roman Catholic Church was met with heavy criticism in the Croatian society in the 11th century, which led to a schism in the Croatian church. [ 15 ]


Among the Christian  Habesha  highlanders of  Ethiopia  and  Eritrea  (the predominantly orthodox Christian  Amhara  and  Tigray - Tigrinya ), it is a tradition to be able to recount one's paternal ancestors at least seven generations away starting from early childhood, because "those with a common patrilineal ancestor less than seven generations away are considered 'brother and sister' and may not marry." The rule is less strict on the mother's side, where the limit is about four generations back, but still determined patrilinearly. This rule does not apply to Muslims or other ethnic groups. [ 16 ]


The  Quran  at 4:22–24 states. "Forbidden to you in marriage are: your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters." [ 17 ]  Therefore, the list of forbidden marriage partners, as read in the Qur'an, Surah 4:23, does not include first cousins. [ 18 ]   Muhammad  himself married his first cousin  Zaynab bint Jahsh . [ 19 ] [ better source needed ]


Financial incentives to discourage consanguineous marriages exist in some countries:  mandatory premarital screening for inherited blood disorders has existed in the UAE since 2004 and in Qatar since 2009, whereby couples with positive results will not receive their marriage grant. [ 20 ]


Genetically, consanguinity derives from the reduction in variation due to  meiosis  that occurs because of the smaller number of near ancestors. Since all humans share between 99.6% and 99.9% of their  genome , [ 22 ]  consanguinity only affects a very small part of the sequence. If two siblings have a child, the child has only two rather than four grandparents. In these circumstances, the probability is increased that the child will inherit two copies of a harmful  recessive gene  ( allele ) (rather than only one, which is less likely to have harmful effects).


Genetic consanguinity is expressed as defined in 1922 by Wright [ 23 ]  with the  coefficient of relationship   r , where  r  is defined as the fraction of  homozygous  due to the consanguinity under discussion. Thus, a parent and child pair has a value of  r =0.5 (sharing 50% of DNA), siblings have a value of  r =0.5, a parent's sibling has  r =0.25 (25% of DNA), and first cousins have  r =0.125 (12.5% of DNA). These are often expressed in terms of a percentage of shared DNA but can be also popularly referred to as % of genes although that terminology is technically incorrect.


As a working definition, unions contracted between persons biologically related as second cousins or closer ( r  ≥ 0.03125) are categorized as consanguineous. This arbitrary limit has been chosen because the genetic influence in marriages between couples related to a lesser degree would usually be expected to differ only slightly from that observed in the general population. Globally it is estimated that at least 8.5% of children have consanguineous parents. [ 24 ]


In clinical genetics, consanguinity is defined as a union between two individuals who are related as second cousins or closer, with the inbreeding coefficient (F) equal or higher than 0.0156, where (F) represents the proportion of genetic loci at which the child of a consanguineous couple might inherit identical gene copies from both parents. [ 25 ]


It is common to identify one's  first- and second-degree cousins, and sometimes third-degree cousins. It is seldom possible to identify fourth-degree cousins, since few people can trace their full family tree back more than four generations. (Nor is it considered important, since fourth cousins tend to be genetically no more similar to each other than they are to any other individual from the same region.) [ 26 ]


Reasons favoring consanguinous marriage have been listed as higher compatibility between husband and wife sharing same social relationships, couples stability, enforcing family solidarity, easier financial negotiations and others. [ 25 ] : 187   Consanguinity is a deeply rooted phenomenon in 20% of the world population, mostly in the Middle East, West Asia and North Africa. [ 25 ]  Globally, the most common form of consanguineous union is between first cousins, in which the spouses share  1 ⁄ 8  of their genes inherited from a common ancestor, and so their progeny are homozygous (or more correctly autozygous) at  1 ⁄ 16  of all loci ( r  = 0.0625). [ 27 ]  Due to variation in geographical and ethnic background and the loci chosen to genotype there is some 2.4% variation expected. [ 28 ]


Historically, some European nobles cited a close degree of consanguinity when they required convenient grounds for divorce, especially in contexts where religious doctrine forbade the voluntary dissolution of an unhappy or childless marriage. [ 29 ]


In the Arab world, the practice of marrying relatives is common. According to the Centre for Arabic Genomic Research, between 40% and 54% of UAE nationals' marriages are between family members, up from 39% in the previous generation. Between 21% and 28% of marriages of UAE nationals were between first cousins. [ 20 ] [ 30 ]  Consanguineous marriage is much less prevalent in Christian Arabs as they do not practice arranged marriages. [ 31 ] [ 32 ] [ 33 ] [ 34 ]  Additionally, an  indult dispensation  is required to marriages contracted between first cousins or closer in Arab Christian denominations in communion with the  Roman Catholic Church , and the  Greek Orthodox Church ; there are no similar regulations that apply to first-cousin marriages in the Coptic Orthodox Church. [ 34 ]


In Egypt, around 40% of the population marry a cousin. A 1992 survey in Jordan found that 32% were married to a first cousin; a further 17.3% were married to more distant relatives. [ 35 ]  67% of marriages in  Saudi Arabia  are between close relatives as are 54% of all marriages in  Kuwait , whereas 18% of all  Lebanese  were between blood relatives. The incidence of consanguinity was 54.3% among Kuwaiti natives and higher among Bedouins. [ 36 ]


It has been estimated that 55% of marriages between Pakistani Muslim immigrants in the United Kingdom are between first cousins, [ 37 ]  where preferential patrilateral parallel  cousin marriage , i.e. a man marrying the daughter of his father's brother, is favored.


Double first cousins  are descended from two pairs of siblings, and have the same genetic similarity as half-siblings. In unions between double first cousins, the highest  inbreeding  coefficients are reached, with an (F) of 0.125, for example among Arabs and uncle-niece marriages in South India.


The early days of colonization, particularly from 1660 to 1680, gave French Canadians genetic traits that are still present today, owing to the isolation and low population of the early colony. This has led to the province having a higher rate of  hypercholesterolemia ,  tyrosinemia , spastic  ataxia , intestinal  atresia ,  myotonic dystrophy , etc., in the population than anywhere else in the world. [ 38 ]


The phenomenon of inbreeding increases the level of homozygotes for autosomal genetic disorders and generally leads to a decreased  biological fitness  of a population known as  inbreeding depression , a major objective in clinical studies. [ 39 ]  While the risks of  inbreeding  are well-known, informing  minority group  families with a  tradition  of  endogamy  and changing their behavior is a challenging task for  genetic counseling  in the health care system. [ 40 ]  The offspring of consanguineous relationships are at greater risk of certain genetic disorders.  Autosomal recessive  disorders occur in individuals who are  homozygous  for a particular recessive gene  mutation . [ 41 ]  This means that they carry two copies ( alleles ) of the same gene. [ 41 ]  Except in certain rare circumstances (new mutations or  uniparental disomy ) both parents of an individual with such a disorder will be carriers of the gene. [ 41 ]  Such carriers are not affected and will not display any signs that they are carriers, and so may be unaware that they carry the mutated gene. As relatives share a proportion of their genes, it is much more likely that related parents will be carriers of an autosomal recessive gene, and therefore their children are at a higher risk of an autosomal recessive disorder. [ 42 ]  The extent to which the risk increases depends on the degree of genetic relationship between the parents; so the risk is greater in mating relationships where the parents are close relatives, but for relationships between more distant relatives, such as second cousins, the risk is lower (although still greater than the general population). [ 43 ]


Consanguinity in a population increases its susceptibility to infectious  pathogens  such as  tuberculosis  and  hepatitis  but may decrease its susceptibility to malaria and other pathogens. [ 44 ]


The  consort kin  or  outer kins  ( Chinese :  外戚 ;  pinyin :  wàiqì ) were the  kin  or a group of people related to an  empress dowager  or a  consort  of a monarch or a  warlord  in the  Sinosphere . The leading figure of the clan was either a (usually male)  sibling ,  cousin , or  parent  of the empress dowager or consort.


Consort kins can be seen as a manifestation of  nepotism  in Sinospheric imperial politics. While some were competent, only relying on their female relatives for their initial audiences with the emperor and then proving their worth at their positions (e.g.  Wei Qing  and  Huo Qubing ), many turned out to be corrupt and incompetent (e.g.  Yang Guozhong ). Corrupt and incompetent consort kins have been linked to the downward turn of fortunes for many dynasties.


Sixteen Kingdoms


A  cousin  is a relative that is the child of a parent's sibling; this is more specifically referred to as a  first cousin .


More generally, in the  kinship  system used in the English-speaking world, a cousin is a type of  relationship  in which relatives are two or more  generations  away from their most recent common ancestor. For this definition degrees and removals are used to further specify the relationship.


Degree measures how distant the relationship is from the most recent common ancestor(s). If the cousins do not come from the same generation, removal is specified, as removal measures the difference in generations between the two cousins.  When the removal is not specified, no removal is assumed. [ 1 ] [ 2 ]


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 in law, a first cousin is a type of  third-degree relative . [ citation needed ]


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 the other's parent (are not the other's  aunt / uncle  nor  niece/nephew ). [ 2 ]  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. [ 1 ]  The  removal  is the difference between the number of generations from each cousin to the common ancestor. [ 1 ]  Two people can be removed but be around the same age due to differences in birth dates of parents, children, and other relevant ancestors. [ 1 ] [ 3 ] [ 4 ]


For example, David and George are on opposing sides of the family tree and are  first cousins  (David is of the lowest order: one)  with one removal  (the cousins are of order one and two respectively; therefore, the difference in generations to the common ancestor is one).


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.


On the other hand,  parallel and cross cousins  are reciprocal relationships. Parallel cousins are descended from same-sex siblings. 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 cousin and paternal cousin to each other. [ 9 ]  In the  basic family tree  example, David and Emma are cross cousins.


Double cousins are relatives who are cousins from two different branches of the family tree. 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 their  parents  and are thus doubly related. Double first cousins share both sets of  grandparents .


Half cousins are descended from half siblings and would share one 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 and would share one grandparent on each side.


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 ]


Step-cousins are either stepchildren of an individual's aunt or uncle, nieces and nephews of one's step-parent, or the children of one's parent's step-sibling. [ 14 ]  A cousin-in-law is the cousin of one's spouse or the spouse of one's cousin. [ 15 ]


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 one has with oneself. Consanguinity decreases by half for every generation 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. [ 16 ]


Between first cousins, there are two shared ancestors each with four generations of separation, up and down the family tree:

 (

 1
 2

 )

 4

 +

 (

 1
 2

 )

 4

 {\displaystyle \left({\tfrac {1}{2}}\right)^{4}+\left({\tfrac {1}{2}}\right)^{4}}

 ; their consanguinity is one-eighth. For each additional removal of the cousin relationship, consanguinity is reduced by half, as the generations of separation increase by one. For each additional degree of the cousin relationship, consanguinity is reduced by a quarter as the generations of separation increase by one on both sides. [ 16 ]


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 first 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. [ 16 ]


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


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. [ 17 ] [ 18 ]  Cousin marriages are often  arranged . [ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ]  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 or second cousins (in some of the countries in this region, this may exceed 70%). [ 22 ]  Just outside this region, it is often legal but infrequent. Many cultures have encouraged specifically cross-cousin marriages. [ 23 ]  In other places, it is  legally prohibited  and culturally equivalent to  incest . [ 24 ] [ 25 ]  Supporters of cousin marriage often view the prohibition as  discrimination , [ 26 ] [ 27 ]  while opponents claim potential  immorality . [ 28 ]


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. [ 29 ]  Due to the risk that the trait is harmful, children of high-consanguinity parents have an increased risk of  recessive genetic disorders .


Closely related couples have more children. Couples related with consanguinity equivalent to that of third cousins have the greatest  reproductive success . [ 30 ]  This seems counterintuitive 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. [ 31 ]


This risks of inbreeding - particularly through common practice of cousin marriage - extend beyond the immediate descendants of those involved. Sustained cousin marriage within a population group over generations eventually leads to  inbreeding  at the population level and the rise of genetic disorders that affects the entire population, not just those in cousin marriages. [ 32 ]  Increased  genetic literacy  within a population can lead to a reduction in cousin marriage. [ 33 ] [ 34 ]


Crow kinship  is a  kinship  system used to define  family . Identified by  Lewis Henry Morgan  in his 1871 work  Systems of Consanguinity and Affinity of the Human Family , the Crow system is one of the six major kinship systems ( Eskimo ,  Hawaiian ,  Iroquois , Crow,  Omaha , and  Sudanese ). [ 1 ]


The system is somewhat similar to the  Iroquois system , but distinguishes between the mother's side and the father's side. Relatives on the mother's side of the family have more descriptive terms, and relatives on the father's side have more classificatory terms.


The Crow system is distinctive because unlike most other kinship systems, it chooses not to distinguish between certain generations.  The relatives of the subject's father's matrilineage are distinguished only by their sex, regardless of their age or generation.  In contrast, within Ego's own matrilineage, differences of generation are noted.  The system is associated with groups that have a strong tradition of  matrilineal descent .  In doing so, the system is almost a mirror image of the  Omaha system , which is  patrilineal .


As with the Iroquois system, the Crow uses bifurcate merging, meaning that there is a distinction between collateral relatives of different gender in Ego's descent group. In this case, father's brother would be called "father's brother", and mother's brother would be called "uncle". [ 2 ]   Only the  Iroquois system  uses bifurcate merging as a secondary name.


The system is named for the  Crow Tribe  of  Montana .  The system appears frequently among various cultures.  In the Southwestern US, it has traditionally been part of the  Hopi Indian  culture and the  Navajo Nation .


Daughter preference  describes human families seeking to bear and raise daughters, rather than sons.


Daughter preference is evident in contemporary Japan [ 1 ]  and Japanese-American immigrant families. [ 2 ]  South Korea has also demonstrated a measurable shift from son preference to daughter preference. [ 3 ]  Daughter preference appears at measurable levels in three Scandinavian countries: Denmark, Norway, and Sweden. [ 4 ]  One study found that a significant contributing factor to daughter preference was the "number of wife's sisters." [ 5 ]  In the  matrilineal  inheritance system of  Malawi , daughter preference emerges if all existing children are sons. [ 6 ]


Daughter preference or  son preference  is sometimes expressed by higher levels of household investment in offspring of preferred gender. [ 7 ]


A  dibling,  a  portmanteau  of donor  sibling , [ 1 ] [ 2 ]  or donor-conceived sibling, [ 3 ]  or donor-sperm sibling, [ 4 ]  is one of two or more individuals who are biologically connected through  donated eggs  or  sperm . [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]   This term is also commonly used in children biologically related through embryo donation. In tis instance, the children are full not half biological siblings. The term is not favored among some recipient parents, who prefer the use of  half-sibling . [ 10 ]


People born from anonymous or ID release sperm or egg donation are able to find half-siblings conceived using the same gamete donor online through the  Donor Sibling Registry [ 5 ]  or by using commercially-available DNA test kits. DNA testing is more accurate because it relies on comparison of  single-nucleotide polymorphisms  instead of gamete donor identification numbers (which may be erroneous). [ citation needed ]


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Disownment  occurs when a parent renounces or no longer accepts a  child  as a family member. Disownment might be due to actions perceived as reprehensible or lead to severe emotional consequences. Different from giving a child up for  adoption , it is a  social  and  interpersonal  act and may take place later in the child's life, which means that the disowned child would have to make arrangements for future care. Among other things, it implies no responsibility for future care, making it similar to  divorce  or  repudiation  (of a spouse), meaning that the disowned child would have to find another residence to call home and be cared for.


Disownment may entail  disinheritance , familial exile, or  shunning , or all three. A disowned child might no longer be welcome in their former family's home or be allowed to attend major  family events . Conversely, a child might themselves seek to disown their parents or family through some form of  emancipation .


In some countries, disownment of a child is a form of  child abandonment  and is illegal when the child is a minor. Some countries condition a legal right of disownment within the family on evidence of specific familial conditions, such as an absence of normal familial ties (required in  Austria ), or abuse on the part of the person sought to be disowned (required in  Spain ). [ 1 ]


In Roman law, the rights called  patria potestas  included power of disownment. [ 2 ]  As to Italian law, see article 224 of the Civil Code. [ 3 ]  There was a process for disownment amongst the  Tanala  of Ikongo, [ 4 ]  and disownment was inflicted as a punishment by the  antandroy . [ 5 ]  There was provision for disownment in the  Code of Hammurabi . [ 6 ]  In Louisiana, the right to disown a child was called  action en desaveu . [ 7 ]


In some cases, society and its institutions will accept an act of disownment.


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This  family -related article is a  stub . You can help Wikipedia by  expanding it .


Eskimo kinship  is a category of  kinship  used to define family organization in  anthropology . Identified by  Lewis H. Morgan  in his 1871 work  Systems of Consanguinity and Affinity of the Human Family , the  Eskimo  system was one of six major kinship systems (Eskimo,  Hawaiian ,  Iroquois ,  Crow ,  Omaha , and  Sudanese ). [ 1 ]  The system of English-language kinship terms falls into the Eskimo type.


The  joint family  system places no distinction between  patrilineal  and  matrilineal  relatives; instead, it focuses on differences in kinship distance (the closer the relative is, the more distinctions are made). The system emphasizes the  nuclear family , identifying directly only the mother, father, brother, and sister.  All other relatives are grouped together into categories. It uses both  classificatory  and  descriptive  terms, differentiating between gender, generation, lineal relatives (relatives in the direct line of descent), and collateral relatives (blood relatives not in the direct line of descent). The Eskimo system is defined by its "cognatic" or "bilateral" emphasis - no distinction is made between patrilineal and matrilineal relatives.


Parental siblings are distinguished only by their sex (aunt, uncle). All children of these individuals are lumped together regardless of sex (cousins).  Unlike the  Hawaiian system , Ego's parents are clearly distinguished from their siblings.


The Eskimo system is relatively common among the world's kinship systems, at about 10% of the world's societies. [ 2 ]  It is now common in most Western societies (such as those of Europe or the Americas). In addition, it is found among a small number of  food-foraging  peoples such as the  ǃKung  tribe of Africa and the Inuit (Inuit- Yupik ) for whom it is named.