Is having a physical relationship with my sister wrong?

In this blog post, we answer whether having a physical relationship with one’s sister is wrong.

We define the term incest and point out the biological, psychoanalytic, demographic explanations of incest.

“I am having a physical relationship with my sister” – what should I do?

If you are having a physical relationship with your sister, you should know that is considered illegal and morally wrong in most of the countries of this world. 

Psychologists talk about multiple cases in which a brother and a sister who grew up separated in childhood meet again and fall in love with each other. 

If you are in this situation (you did not grow up with your brother/sister) and you feel that you have fallen in love with him, it can help you better understand why this is happening.

It is perfectly explainable why a person can fall in love with his or her brother or sister once he/she sees him/her again after a long separation.

It’s about what you recognize in that person – you recognize parts of yourself and your parents, you recognize aspects that are so familiar and yet new. 

Every person is attracted to certain traits similar to his own (and siblings have similar traits, even similar levels of intelligence, even similar interests and abilities), but also traits that seem familiar (these are traits that the person remembers to loved ones in childhood: parents, grandparents, other significant adults in the life of the young child). 

Therefore, this similarity and familiarity suddenly found in a person gives birth to an intense attraction, an attraction that takes the form of romantic or passionate love, even if normally a brother and a sister would not have such a connection.

Why does it happen most often that someone falls in love with his brother or sister after they have been separated for a long time?

Simple: when a brother and a sister grow up together, share the same house and sometimes even the same room, there is a so-called “desensitization” of the attraction.

It is an effect that is believed to be naturally programmed to prevent incest. 

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: for example, children who are raised together, once adults, do not feel attracted to each other, looking for more distant partners.

They have simply become too familiar, too close, so they feel brotherly love and not a romantic and physical one.

On the other hand, if two children grow up separately, once they see each other again, they can feel that deep connection given by genetics and can interpret it as romantic love (there is the feeling that you have found your soulmate because a brother or a sister does not only share common traits but also share something of your being, genetic material and maybe spirit). 

There is a certain familiarity, but there is no saturation of stimuli – on the contrary, this familiarity is paradoxically perceived as new and exciting. 

Brother and sister are instinctively attracted to each other and because there is no saturation of stimuli to kill any trace of physical attraction, they will fall in love with each other romantically and passionately (there is that unique connection that exists between any brother and sister, but is doubled by attraction). 

The relationship is new, the deep connection between them is old, from their birth.

What is incest?

The name of incest is given to sexual relations practised between individuals who share a direct blood relationship, such as between siblings, parents and children, grandparents and descendants, or whatever the biological or blood relationship between the two individuals.

In many cases, this extends to the cousins, although the greater their distance, the more loosely the relationship will be judged.

Incest is a culturally rejected and forbidden and taboo practice in almost all civilizations, always preferring exogamy (sexual relations with individuals outside the family group) to inbreeding.

There were, however, famous cases of incest throughout history, especially among eccentric or very closed caste rulers, but even those cases are documented as an extravagant and morally challenging phenomenon.

Historical examples of incest

Many stories are told of historical figures who were more or less openly incestuous.

Queen Cleopatra of ancient Egypt is said to have married two of her own brothers, and something similar is reported of the Inca and Hawaiian kings.

Everything points to the fact that these family unions responded to the practical criterion of preserving the power of the throne linked to the family.

Similarly, Nero and Caligula, Roman emperors, are accused of having slept with their mother and sisters, respectively, reinforcing the air of doom and lust with which they associate with decadent Rome.

But the case of the Habsburg Dynasty is also famous, one of the most influential noble houses in Europe, whose members married each other (between cousins) for generations.

The prohibition of incest

Incest is a culturally rejected and even persecuted practice, which in some countries is even illegal, while in others it is tolerated but without any right to legally consecrate the union through marriage.

In almost all religious codes it is viewed as an immoral, forbidden union and its often cursed offspring.

However, cases of incest abound in ancient mythologies and in the Judeo-Christian Bible itself.

Biological explanation of incest

Given that individuals belonging to the same family share a high percentage of their genetic material, incest would represent, from a biological point of view, a union that impoverishes the genetic well, that is, it reduces the genetic variability available for future generations, thus increasing the incidence of hereditary diseases and defects. 

This interpretation values ​​mixing and exogamy, the genetic hybridization between individuals more genetically distant, above the supposed purity of similarity.

Psychoanalytic explanation of incest

Sigmund Freud’s studies on the constitution of the human mind yielded explanations regarding the taboo of incest – one of the fundamental features of civilization.

For Freud, incest would have involved, in the primitive human horde, the confrontation between men for access to the reproduction, which would have confronted brothers or even parents and children.

Thus, the practice would have received all that burden of anguish over the coming violence and would end up being despised, replaced by exogamy.

Social explanation of incest

Another way of understanding the prohibition of incest is of a social nature and is based on the fact that this practice breaks the harmony of the family structure and deteriorates the ties of the family group and its social environment.

Considering that we are a gregarious species, that is, that tends to constitute groups, it is natural for a family nucleus to seek to expand its economic, political or social capacity by uniting rival clans through exogamous marriage, instead of withdrawing into itself with the inbred.

Demographic explanation of incest

Finally, a demographic explanation of the prohibition of incest would affirm that, in the primitive societies of semi-nomadic hunters and gatherers, the mortality rates between young and adults would be very high and this would require greater care of the offspring by the mothers. , which would be old by the time they reached sexual maturity. 

This would have forced young people to seek fertile partners in other social groups.

Possible causes of incest

In principle, there would be no cause for incest other than the attraction between two people, with the exception that they would be two direct relatives.

While it is true that no one chooses who they fall in love with, in many cases incest can also occur in the context of intra-family sexual abuse, which further compounds the case.

However, abuse and incest are two different things.

Possible consequences of incest

Incest can carry many psychological problems.

The consequences of incest are mainly based on social rejection, the emotional or psychological problems they may produce, such as feelings of guilt, etc.

In the case of relations with offspring, in the impoverishment of the genetic well, increasing the risk of mutations and diseases related to it, given that a defective gene present in the family would have twice the chances of manifesting itself, given that it is found in both parents.

Diseases arising from incest

Some inherited diseases have been related to incestuous sexual relations, such as:

  • Down syndrome and other delays. Although this is not the only and exclusive cause of mental retardation, a higher rate of this type of disease has been seen in the offspring of very genetically close individuals.
  • Malformations. Similarly, children born with deformations or with dysfunctional bodies are often the result of incest.
  • Hemophilia. This disease that prevents or hinders the correct blood coagulation has been known as “the disease of the kings” because it was frequent among Spanish kings descendants of noble houses of marked inbreeding tendency.
  • Harlequin disease. Called Harlequin Ichthyosis, it is a very rare genetic skin disease that resembles a harlequin costume in newborns: thick, large scales from around the body and are born with the red-eyed, inverted eyelids.

Incest in culture and art

The Greek god Zeus was a recurring incestuous.

Incest was a very common practice in the mythology of Greco-Roman antiquity, as is the famous case of Oedipus, who unknowingly marries his mother Yocasta and kills his father Laius.

Their offspring, the fruit of the forbidden union, will be cursed and suffer sufferings throughout the generations.

However, the Greek god Zeus was an incestuous recurrent, as he had ample descendants with his sisters Demeter and Hera.

A similar case is that of a militant Islamist group and Osiris, brother gods of Egyptian mythology; or Tau and Kerana, in the Guaraní.

In the Bible, the case of Lot and his daughters is famous: the latter intoxicate him so that they can sleep with him and continue with the lineage, but trying not to be seen when they enter his bed, so they are secretly pregnant.

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In this blog post, we answered whether is having a physical relationship with one’s sister is wrong.

We defined the term incest and point out the biological, psychoanalytic, demographic explanations of incest.

As a summary, there are enough cases of romantic and passionate love between brother and sister to convince us that yes, sibling incest can happen.

The first and most important thing is to try to understand the nature of your feelings and why brotherly love seems to have turned into romantic, passionate love.

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

FAQ about having a physical relationship with sister

Are sisters attracted to their brothers?

There are cases when sisters feel attracted to their brothers, however, this is not common!

Sometimes, when siblings grow apart, they later meet and fall in love.

The reason behind this is the familiarity of their traits, that makes them believe they have found the ideal partner.

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 incest. 

Is it illegal to sleep with your cousin?

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

What is it called when a daughter is attracted to her father?

When a daughter between the age of 3 and 6 is attracted to her father we may speak of the Electra complex

What we recommend for Relationship & LGBTQ issues

Relationship counselling

  • If you are having relationship issues or maybe you are in an abusive relationship then relationship counselling could be your first point of call. Relationship counselling could be undertaken by just you, it does not require more than one person.

LGBTQ issues

If you are dealing with LGBTQ issues then LGBTQ counselling may be a great option for you. Maybe you are confused as to your role and identity or simply need someone to speak to. LGBTQ counsellors are specially trained to assist you in this regard.


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

Pendergrast, M. (1995). Victims of memory: Incest accusations and shattered lives. 

“Incest”. Author: Julia Máxima Uriarte. To: Last edition: March 10, 2020.

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