What family members can you marry in the UK? (and who you can’t)

In this blog post, we will answer the following question: What family members can you marry in the UK? We also tell you who you cannot legally marry in the UK and why do we consider sexual relationships between family members inc**t. 

What family members can you marry in the UK?

According to the Marriage (Prohibited Degrees of Relationship) Act 1986, the following family members can marry in the UK:

• “A marriage between the daughter/grand-daughter and her step-father (whether her mother/grandmother is living or not) OR between half-cousins (whether the step-parent is living or not) as long as both parties are at least 21 years of age and they have not lived under the same roof until the age of eighteen.

• A marriage between a man and a woman who is the grandmother of a former spouse of his (whether the former spouse is living or not) OR is a former spouse of his grandson (whether his grandson is living or not).”

• The marriage of a woman and a man who is the grandfather of a former spouse of hers or is a former spouse of her grand-daughter; and

• under certain conditions, the marriage of persons related in certain other degrees of affinity. For example, an adopted child may marry his adoptive siblings.

People wonder whether they can marry their half-niece?

Who can you not marry in the UK?

In the UK you are not allowed to marry:

• Your child, including an adopted child.
• Either of your parents, including an adoptive parent.
• You siblings, including half-siblings.
• You aunt or uncle, including a half-uncle or half-aunt.
• Your grandparents.
• Your grandchildren.
• You half-niece or half-nephew. 

Is it legal to marry your niece?

No, it is not legal to marry your niece in most states in the US. There are laws against marrying any of your ancestors or descendants, and this list includes your brother, your sister, your half-brother, your half-sister, your aunt, your uncle, your niece, your nephew, your mother, your father, your grandmother, your grandfather, your great-grandmother and so on.

Half Uncle and Niece Relationship

A half uncle and niece relationship, or marriage, is known as Avunculate marriage, and it is more legal than some other inc**tuous relationships. Even though one could be a half uncle, usually they may not be referred to as such, and just be called uncle

Marriage impediments 

There are four types of kinship impediments to getting married: that of consanguinity, of affinity (these two are the typical ones), that of public honesty (referring to invalid marriages or conspicuous concubinates that was considered as an illicit affinity relationship in the documents) and the legal one (that comes from the adoption), where it is forbidden to marry the adoptive parents or adoptive siblings.

The most common and that one always sees in these Marital Acts are the impediments due to kinship of consanguinity and affinity. 

Those of consanguinity are explained practically alone and it is related to the fact that the couple descended from one or more common ancestors. 

The second, of affinity, refers to the fact that one of the bride and groom had some legitimate or illegitimate relationship with a blood relative of the other groom, it appears written as “impediment of legal affinity” or “impediment of illicit affinity”. 

For example, if the groom wants to contract a second marriage with his first wife’s sister, they will have a lawful affinity relationship between the two, but if the groom had sexual relations with the bride’s sister (no marriage involved) they will have an illicit affinity kinship, which is the one of public honesty raised before. 

On the other hand, it was not and is not allowed to marry between descendants of the same straight line, that is, between parents and children or grandparents with grandchildren. Neither was it possible to marry by cross or collateral line between siblings or half-siblings. 

Why do we consider sexual relations between members of the same family ‘inc**t’?

The sexual relationship between relatives within the degrees in which marriage is prohibited ’is known as‘ inc**t ’.

The term inc**t comes from the Latin ‘inc**tus’, formed by the negation prefix ‘in’ (not) and ‘castus’ (chaste, pure) giving it the literal meaning of ‘not chaste’ / ‘impure’, applying to all that type relationship that was not well seen: adultery, non-consensual relationships, through prostitution, with members of the same family, eventually leaving the word to define only this last meaning.

It should be borne in mind that throughout history, innumerable are the cases in which blood relatives have had some kind of carnal relationship (and not only because of the sexual issue but many of them to get married). There are multiple weddings performed in loyalty between members of the same family clan. There have also been many cases among the lower classes, who married among close relatives in order not to have to contribute a dowry.

Despite the many cases reported in the Bible in which flagrant cases of ‘inc**t’ appear, in the Middle Ages the Church pressed to legislate and put an end to marriages between relatives and which was known as ‘Marital impediment of consanguinity’ ( hence the degrees in which the marriage mentioned in the first paragraph is prohibited), defined in the following degrees of relationship:

Straight-line: grandparents with grandchildren, parents with children (thus to infinity, that is, between all the ancestors and descendants of the same family), or in collateral line: between brothers, between uncles with nephews, between cousins-brothers, etc.

Only the local bishop was the one who could dispense the marriage between first cousins (this being the closest degree of kinship that was allowed to marry each other). We must keep in mind that family ties encompass inbreeding and adoption.

It should be noted that today in a large number of countries inc**t is decriminalized (as long as there is no illegality, for example maintaining unwanted relationships or with minors) allowing blood relatives to maintain a sentimental/sexual relationship between them, but not being allowed to contract marriage (paradoxes of the laws).

In the primitive tribes, young people looked for their partner outside the group – in some societies women left and in others, men – and these marital ties favoured alliances with other lineages, which strengthened the family nucleus and reduced the possibility of confrontations with neighbours, but there is also a biological reason. 

When human beings are paired with their relatives over several generations, the risk of inherited diseases increases; individuals become less fertile and reproduce less. In other words, evolution rewards the dispersion of genetic inheritance and punishes its concentration.

An argument that reinforces the biological interpretation is that also some animal species avoid mating with members of their family. In species such as chimpanzees or spider monkeys, females must leave their natal groups when they reach sexual maturity and search for a new one. In the cappuccinos or the macaques, it is the opposite, it is the males that must leave the group. 

An adaptive mechanism that guarantees that this rule is met is the development of sexual rejection towards the people with whom we live; The so-called Westermarck effect is established in early childhood, but, according to some scientists, it would also explain the decrease in desire in long-term marriages.

Suppressing sexual attraction to avoid inc**t

But how would you do natural selection to promote inc**t avoidance behaviours? After all, there is no trait by which we can recognize brothers and sisters with the naked eye. 

According to Westermarck, evolution has decided to pull statistics to create a mechanism of aversion between relatives. As people who see each other daily and belong to the same environment during the first years of life have many possibilities of being related, the criterion used to suppress sexual attraction is the existence or not of proximity during childhood.

This predisposition to not be attracted to the people with whom we come in contact periodically during the first moments of our lives would be genetically based and would represent an evolutionary advantage; but as a result of this, we would also have no sexual interest in old childhood friendships, for example.

Conclusions

In this blog post, we answered the following question: What family members can you marry in the UK? We also told you who you cannot legally marry in the UK and why do we consider sexual relationships between family members inc**t. 

To summarize: In the UK you can legally marry some of your half-relatives, adoptive family members (excepting the parents) and certain other degrees of affinity. 

You cannot marry: 

• Your child, including an adopted child.
• Either of your parents, including an adoptive parent.
• You siblings, including half-siblings.
• You aunt or uncle, including a half-uncle or half-aunt.
• Your grandparents.
• Your grandchildren.
• You half-niece or half-nephew. 

If you have any questions or comments on the content, please let us know!

FAQ on What family members can you marry in the UK?

References

DeYoung, M., & Lowry, J. A. (1992). Traumatic bonding: Clinical implications in inc**t. Child Welfare: Journal of Policy, Practice, and Program, 71(2), 165–175.

Pendergrast, M. (1995). Victims of memory: Inc**t accusations and shattered lives. 

“Inc**t”. Author: Julia Máxima Uriarte. To: Characteristics.co. Last edition: March 10, 2020.

Legislation.gov.uk – Marriage (Prohibited Degrees of Relationship) Act 1986

Genetic-genealogy.co.uk   -FORBIDDEN MARRIAGE LAWS OF THE UNITED KINGDOM

Familytreeforum.com -Forbidden Marriages