How Common Is It For Step Siblings To Marry? | OptimistMinds (2024)

In this article, we will answer the following question: How common is it for step siblings to marry? We will talk about the moral implications of marrying your step-sibling, the Westermarck effect and about Genetic sexual attraction.

How common is it for step siblings to marry?

Many cultural taboos are created around genetic problems. There is nothing biologically wrong with two people who were created by completely different parent pairs being attracted to one another.

Social issues could be an entirely different thing. The longer you may have lived under the same roof, the more strange you may be seen by outsiders. I would say that this is entirely curable by moving to a different community, but without knowing how old and independent the parties are, it is difficult to say if this is practical.

So, as with many issues with which people struggle, it may depend on circumstances, but there is nothing morally repugnant about the situation, you simply have to ask what are the consequences in your community and your family?

Let’s take an example. If your stepsister is your mother’s daughter with another father, she still has half your blood. You are both brothers. I don’t know why if the children are children of the father and of a different mother they are called siblings and if they are children of the mother and of a different father they are called stepbrothers.

Now: if they are two different families, that is, that your stepsister was the daughter of your stepfather or your stepmother but you do not have any blood relationship, I do not know how legal things will go with that.

The blood issue is because children inherit diseases and acquire others. It is like half-inc**t.

Can you marry a step sibling?

Yes, you can marry a step sibling, because stepsiblings are not blood relatives, which means that there is no risk of any genetic disorders carrying through them to their children. Step Siblings are legally free to marry each other and in the US there are no state laws that prohibit marriage.

Is it illegal for step siblings to marry?

No, it is not illegal for step siblings to marry, but it is not seen in a positive light by society. It is illegal for siblings to marry because in this case the chances of genetic disorders in their children, but this is not the case with step siblings. Step siblings are related through their parents’ marriage, and not by blood, which is why it is legal for them to get married.

Why do most people feel the rejection of a sibling relationship, even if it is consensual?

The answer is inc**t taboo. In the vast majority of cultures, sexual relations between relatives with different degrees of consanguinity – parents with sons and daughters, brothers among themselves and, to a lesser extent, cousins – are not socially accepted. Sometimes they are also legally prohibited.

One explanation is the rule of exogamy: 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.

The Westermarck effect: lack of desire for childhood friends

Many people are interested in knowing what characteristics and styles of behaviour enhance personal attractiveness, but fewer also try to know things about the factors that kill any possibility of attraction.

That is why it is not surprising that so little is known about the Westermarck effect, a hypothetical psychological phenomenon according to which human beings are predisposed not to feel sexual desire towards the people with whom we interact continuously during our early childhood, independently whether they are related or not.

Why might this curious trend occur? The explanatory proposals that many researchers are considering to solve the unknown of the Westermarck effect have to do with the phenomenon of inc**t.

The probability

Edvard Alexander Westermarck was a Finnish anthropologist born in the mid-19th century known for his theories about marriage, exogamy, and inc**t.

Regarding the latter, Westermarck proposed the idea that avoidance of inc**t is the product of natural selection. For him, avoiding reproduction between family members would be part of an adaptive mechanism that we carry in our genes and that would have spread among the population due to the advantage of this behaviour in evolutionary terms.

Since offspring from inc**t can have serious health problems, selection would have carved out in our genetics a mechanism for us to dislike it, which in itself would be an adaptive advantage.

Ultimately, Westermarck believed that natural selection has shaped the sexual tendencies of our entire species by preventing relationships between close relatives.

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.

Genetic sexual attraction

The curious thing is that the scientific literature describes that imprint that leads us to avoid relationships with close relatives or childhood friends, but also an apparently contradictory phenomenon: genetic sexual attraction, by which members of a family who grow up separated (step-siblings for example) can feel attracted when they are older.

This syndrome has become known in recent years due to the reunions between relatives who had lived in different homes as a result of adoption processes.

Patrick Stübing and Susan Karolevski grew up separated because he was given up for adoption at the age of 3 in Leipzig (Germany). Two decades later, he met his biological family and began a relationship with his 16-year-old sister, who suffered from slight mental retardation.

They had four children: two of them have severe intellectual disabilities, one was born with congenital heart disease and the fourth is normal. As inc**t is illegal in Germany, Stübing was imprisoned and the custody of the three older children was taken from them. The case was very controversial – a sector of society asked to break “the last taboo” – but in 2012 the Strasbourg Court ruled in favour of German Justice.

There is a group of inherited diseases, that to manifest require that both copies of the gene are mutated. In this case, if the parents are relatives, their descendants have a 50% chance of being carriers of the disease and a 25% chance of suffering from it.

Although the probabilities that the children suffer anomalies depend on the degree of consanguinity, it is calculated that they are close to twice that of people without a relationship. Phenylketonuria, cystic fibrosis or porphyria are some ailments of this group.

FAQ on How common is it for step siblings to marry?

Do people marry their step-siblings?

Generally, people can marry their step-siblings, unless the law in their country prohibits it. If step-siblings are not related by blood, they can get married and even have children. However, marriage between people who are related by blood is illegal.

Is marrying your step-sibling illegal?

Marrying your step-sibling, if you are not related by blood, is not illegal. Otherwise, marriage between people who are related by blood (sibling, parent, grandparent, child, grandchild, stepparent, grandparents’ spouse, spouse’s child, spouse’s grandchild, sibling’s child or parent’s sibling) is punished by law in most countries of the world.

Is it normal to be attracted to family members?

It is not normal to be attracted to family members, however, there are enough cases out there to prove that this happens. There is even a term for this, called Genetic Sexual Attraction, or GSA.

Why don’t we find our siblings attractive?

We do not find our siblings attractive because we grew up too close to them. The constant closeness leads to saturation of stimuli and too much familiarity between brother and sister, which kills any attraction. This can be seen even in people who are not relatives, but who grow up in the same house.

What is it called when you are attracted to your sibling?

When you are attracted to your sibling, you may speak of Genetic sexual attraction. GSA means that a strong sexual attraction may develop between close blood relatives, but only when the two first meet as adults. In other cases, we speak about inc**t.

Is it illegal to sleep with your cousin?

In most countries, yes it is illegal to sleep with your cousin, parent, grandparent, sibling.


In this article, we answered the following question: How common is it for step siblings to marry? We talked about the moral implications of marrying your step-sibling, the Westermarck effect and about Genetic sexual attraction.

As a summary, there are enough cases of romantic and passionate love between brother and sister to convince us that sibling inc**t can happen. There is nothing biologically wrong with two people who were created by completely different parent pairs being attracted to one another.

However, you should consider that social issues could be an entirely different thing. The longer you may have lived under the same roof, the more strange you may be seen by outsiders.

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


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: Last edition: March 10, 2020. – Is it Illegal for Step-Siblings to Marry? – In What States Is It Illegal to Marry Step-Siblings?

How Common Is It For Step Siblings To Marry? | OptimistMinds (2024)


Is it common for step-siblings to marry? ›

It is relatively uncommon for step-siblings to get married. The idea of step-siblings marrying each other can be seen as socially taboo and can be met with disapproval in some communities. While step-sibling marriage is not very common, it has been known to happen in some cases.

How common is it for step-siblings? ›

About one in six children in the United States—more than previously thought—live with half- or step-siblings just before starting kindergarten.

Can non blood step-siblings marry? ›

No you cannot marry your step sister. Even if you are not related in blood ties, however still both of you will come under the relationship of step siblings as a result you and your step sister will come under the purview of prohibited degree of relationship. Thus you cannot marry your step sister.

Can step-siblings be blood related? ›

Step-siblings are children born of two different families who have been joined by marriage, A male step-sibling is a stepbrother and a female is a stepsister. The step-siblings relationship is connected through law and is not a blood relation. Step-siblings are sometimes abbreviated informally as stepsibs.

Is dating a step-sibling OK? ›

We all know that some might think the relationship you describe is questionable, but you aren't related by blood, so by law, you are not forbidden to date, or even marry. Truth is, relationships as you describe are most often frowned upon when the kids are raised as siblings — and they are still living in the home.

Can I marry my half sister? ›

Still, sibling marriage is legally prohibited in most countries worldwide. Exceptions include Brazil and Sweden; in both countries, marriages between half-siblings are legally permitted. Sibling marriage was historically practiced in ancient Egypt and Inca tribes.

Are step-siblings legally family? ›

Since stepsiblings are not blood relatives, they are legally free to marry each other. There are no state laws that prohibit marriage between stepsiblings since they are not at risk of having children with genetic defects due to being close blood relatives.

Are step-siblings immediate family members? ›

For purposes of subdivision (d) of Labor Code Section 2066, "immediate family member" means spouse, domestic partner, cohabitant, child, stepchild, grandchild, parent, stepparent, mother-in-law, father-in-law, son-in-law, daughter-in-law, grandparent, great grandparent, brother, sister, half-brother, half-sister, ...

Are step-siblings considered family? ›

Siblings Are Family, No Matter What the Terms Are

There are some technical differences between blood-related siblings, stepsiblings, half siblings, and adopted siblings. And just like any family, the relationships between siblings can offer unique challenges.

What is the closest blood relative you can marry? ›

In the United States, second cousins are legally allowed to marry in every state. However, marriage between first cousins is legal in only about half of the American states. All in all, marrying your cousin or half-sibling will largely depend on the laws where you live and personal and/or cultural beliefs.

Can ex step-siblings get married? ›

There are also no laws in place saying step-siblings can't legally marry or get together, like there are for actual siblings. So, there you have it. Being with your ex-step sibling isn't entirely taboo — especially if the family aspect of the relationship is as insignificant as Cher and Josh's.

Are half siblings still blood related? ›

Half siblings only share DNA from one parent. The genetic information from the other parent is different. Since both parents give us an equal amount of our DNA, it doesn't matter if two kids share mom's or dad's genetic information. Either way, it's half.

What is it called when you have the same mom but different dads? ›

They may share the same mother but different fathers (in which case they are known as uterine siblings or maternal half-siblings), or they may have the same father but different mothers (in which case, they are known as agnate siblings or paternal half-siblings.

How much DNA do half siblings share? ›

Half siblings share 25 percent of their DNA. 50 percent of each half sibling's DNA comes from the shared parent, and they inherited about half of the same DNA from that parent as one another.

What if a brother and sister have a child together? ›

The risk for passing down a genetic disease is much higher for siblings than first cousins. To be more specific, two siblings who have kids together have a higher chance of passing on a recessive disease to their kids.

Can step-siblings marry in Japan? ›

The Japanese Civil Code forbids the marriage of persons who are related by blood, adoption, or through other marriages. If you are residing illegally in Japan, you cannot obtain the necessary documents in order to be married and any attempt to do so may result in your deportation.

Can you date your half sister? ›

Well that's up to you and her. There are no laws restricting dating. But if you mean dating and later marrying, well that's a different story, as most countries have laws regarding marriage. In many places it is not legal as you're blood relatives, either by common mother or father.

Can I marry my step sister in Islam? ›

But with regard to you, this stepdaughter is not a mahram for the son of her mother's husband, so it is permissible for you to marry her , and there is no problem in that. And Allah knows best.

What is the meaning of ghost marriage? ›

The “ghost marriage” is a practice similar to the levirate, whereby a woman marries a man in the name of his deceased brother. This rare form of alliance is found in very few cultures and aims at ensuring the legacy of a lineage.

Which king married his own daughter? ›

In conclusion, the story of Shah Jahan's marriage to his own daughter Jahanara is a dark and harrowing chapter in Indian history.

What if my half sister has a baby? ›

the children of half siblings are half cousins.

Are step-siblings still step-siblings after divorce? ›

Can stepsiblings still be siblings after the parents that connected them to each other get divorced? It depends. If they have half-siblings in common, it is more likely that they will continue to be in each other's lives, at the very least, seeing each other at their mutual half-siblings' graduations and weddings.

Am I an only child if I have step-siblings? ›

An only child is a person with no siblings, by birth or adoption.

Do step-siblings share a last name? ›

Yeah, sure, if they have the same father, if they're adopted (with a deed poll) or if the stepfather is a person already bearing the same name, like if he's an uncle (assuming this is in a culture that passes patrilinear family names).

Does step family count as family? ›

Relationship: Half-siblings, step-siblings, and stepparents do not always count as immediate family, depending on the type of relationship that they have with you. Length of Time: In some cases, a long-term relationship might qualify someone as a member of the immediate family even if there are no blood or legal ties.

Do step-siblings share a parent? ›

Meaning of step-sibling in English

a child of your stepfather or stepmother with another person who is not your biological (= related by birth) parent: Step-siblings have no parents in common, whereas half-siblings share one parent.

Is a step daughter considered a relative? ›

The first is by blood, meaning they have the same lineage. The people who qualify for this determination are siblings, children or grandchildren that are related by blood. The second way to determine immediate family is by marriage. These include in-laws and stepchildren.

What do you call a family with step-siblings? ›

A blended family/blended household includes at least one step-parent, stepsiblings, and/or half-siblings. A step-parent is the spouse of the child's biological parent but is not the child's biological parent.

Are half-siblings not real siblings? ›

Are half-siblings considered siblings? Yes, half-siblings are real siblings. Even though half-siblings share one parent instead of the two parents shared by full-siblings, they are genuine sisters and brothers to each other.

Is a step-sibling a half sibling? ›

Unlike siblings (i.e., individuals who genetically share the same mother and father), half siblings share a biological connection to one parent only. Stepsiblings are not genetically related but are linked to each other because their parents have romantically partnered.

Is 2nd cousins inbreeding? ›

First cousins have an inbreeding coefficient of 0.0625. Anything at or above 0.0156, the coefficient for second cousins, is considered consanguineous; that includes relationships between people and their nephews and nieces.

At what point are cousins not related? ›

Cousins are people who share a common ancestor that is at least 2 generations away, such as a grandparent or great-grandparent. You and your siblings are not cousins because your parents are only 1 generation away from you. Simple enough, right?

Who is a double cousin? ›

A double cousin occurs when two siblings from one family marry two siblings from another family and both couples have children. Those children are first cousins to one another twice over, through both of their parents. Double second cousins are the children of double first cousins.

Are step children still related after divorce? ›

Yes and no. Legally speaking, you do not have parental rights or responsibilities toward your stepchild unless you adopt them. Nevertheless, your stepchild may still be your stepchild for tax purposes after a divorce, and as many stepparents know, nothing can take away the special bond you form with your stepchild.

Are you still related after divorce? ›

When you get married, you become a part of your spouse's family, so one of the most painful aspects of divorce is losing your legal connection to these family members. Just because you will no longer be legally related to your in-laws, however, does not mean you cannot be friends.

What does the Bible say about marrying your sister? ›

However, the Bible prohibits relationships with any close blood relative (Leviticus 18:6).

Are half-siblings biologically cousins? ›

It's common for people to have half-siblings since not all children share the same two parents. When you take the Ancestry DNA test, since half-siblings only share 25% of their DNA, they may be categorized as your first cousin.

Can two full siblings have different blood types? ›

Brothers and sisters don't always share the same blood type. The genotype of both parents plays a role in defining the blood type. For instance, children of parents with the genotypes AO and BO may have the blood types A, B, AB, or O. Thus, siblings do not necessarily have the same blood type.

Are half-siblings genetically closer than cousins? ›

Half relationships share half of the expected amount of DNA as full relationships. So full siblings share 50% of their DNA, half-siblings only share 25% of their DNA. Half siblings also wouldn't share any fully matched segments. Half 1st cousins share 6.25% of DNA, while full 1st cousins share 12.5% of DNA.

Can a baby have 2 biological fathers? ›

The biological phenomenon of giving birth to twins with two different biological fathers is called heteropaternal superfecundation. In a rare and surprising event, a 19-year-old Brazilian woman gave birth to twins who belong to two different biological fathers.

Can a baby have 2 fathers? ›

Although this is quite rare it can happen and it's called superfetation. Two babies are conceived from separate acts in two different cycles. These babies can be from the same father or two different men. When heteropaternal superfecundation occurs, the babies are from different fathers.

What is a 3 4 cousin? ›

Three-quarter siblings are siblings who are genetically half way between full siblings and half siblings. This can happen, for example, if they share the same father but different mothers but their mothers are sisters which makes them effectively both half-siblings and first cousins.

Are 5th cousins blood related? ›

Are Fifth Cousins Blood-Related? Fifth cousins are related, but there is a chance they do not share DNA. In fact, there is only a 10-15% chance of sharing genetics with any fifth cousin. Even if you and our fifth cousin are related by blood, the DNA shared will be small, especially when compared to closer cousins.

Are you half-siblings if you have different dads? ›

Full siblings share the same biological mother and father, maternal half-siblings share the same mother only, and paternal half-siblings share the same father only.

Can a half sibling share 13% DNA? ›

The DNA Relatives feature uses the length and number of identical segments to predict the relationship between people. Full siblings share approximately 50% of their DNA, while half-siblings share approximately 25% of their DNA.

What is it called when siblings sleep together? ›

Incest is a word for any kind of sex between family members: parent and child, brother and sister, or cousin and cousin. There are many disturbing things in the world, and incest is near the top of the list. Incest is when people who are related have sex.

What happens when two blood relatives have a baby? ›

When parents are blood relatives, there is a higher risk of disease and birth defects, stillbirths, infant mortality and a shorter life expectancy. To have a child with severe diseases and disorders may cause heavy strain for the family in question.

Have a brother and sister ever had a baby? ›

Yes, many brothers and sisters have had babies together.

Is it legal to marry your step mom? ›

Dear Abby: Regarding your advice to “Smitten,” be aware that some states, including Texas, outlaw marriage to your stepmother as incestuous. Others are Rhode Island, South Carolina, Tennessee and Oklahoma.

Can step siblings marry in China? ›

The law bans marriage between close relatives, which is defined as lineal relatives, blood relative in the direct line of descent, and collateral relatives, such as cousins or uncles, to the third degree of relationship.

What does the Bible say about cousins marrying? ›

Must first cousins be forbidden to marry? In the Bible, and in many parts of the world, the answer is no.

What states can you marry your step sister? ›

There is no U.S. law that makes it illegal for stepsiblings to become lawful husbands and wives. Even though you may be related through your parents' marriage, you are not related by blood, therefore, you are not subject to consanguinity laws, which make it illegal for close blood relatives to get married.

Are you a stepmom if you're not married? ›

In this day and age with so many different types of relationship many people are referred to as 'step parents' but legally to be considered a 'step parent' you have to be married or have been married to the child's biological parent.

Can I marry my sister's step daughter? ›

The daughter of a man's sister's husband, from another wife, is not included in the women who are forbidden for marriage, and thus it is permissible for him to marry her as long as there is no other impediment that prevents that.

What is the lowest age of marriage in the world? ›

Similarly, in Equatorial Guinea and São Tomé and Principe, children can marry at the age of 14 with their parents' consent but have to wait until they are 18 otherwise. There are a considerably high number of countries that allow children to marry at the age of 15 and 16 as long as their legal guardians sign off on it.

What is the legal marrying age in Japan? ›

Who Can Get Married in Japan? Article 731 to 737 of the Japanese Civil Code stipulates the following requirements: The male partner must be 18 years of age or older and the female partner must be 18 years of age or older. A person who is under 18 years of age cannot get married in Japan without a parent's approval.

What is the best age for a woman to get married? ›

Dr. Fisher believes that marriages that take place when the couple is in their late 20s to mid 30s are most successful. "By the time we are getting to the late 20s we have a clear sense of who we are and what we want out of life," he explains.

Is it Godly to marry more than one wife? ›

Though the Bible does not specifically forbid having multiple wives or husbands, it is not God's original plan. The Lord's expectation for marriage is that it be held as a sacred covenant between one man and one woman.

Who married his father's sister in the Bible? ›

Amram married his father's sister Jochebed, who bore him Aaron and Moses. Amram lived 137 years.

Where in the Bible does it say not to marry your brother's wife? ›

Leviticus 20:21 New Living Translation (NLT)

“If a man marries his brother's wife, it is an act of impurity. He has violated his brother, and the guilty couple will remain childless.

Was Joseph and Mary cousins? ›

“Matthew says Joseph was a son of Jacob, and Luke says that he was a son of Heli. It appears, however, that Jacob and Heli were brothers and that Heli was the father of Joseph and Jacob the father of Mary, making Joseph and Mary cousins with the same ancestral lines” (Bruce R.

Is it OK to marry your 4th cousin? ›

It is not illegal to marry your fourth cousin in any state because only 0.2 percent of DNA is shared between the relatives, as opposed to 12.5 percent with a first cousin.

What degree of cousin is safe to marry? ›

In the United States, second cousins are legally allowed to marry in every state. However, marriage between first cousins is legal in only about half of the American states.


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