Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

The Enigma of the Incest Taboo

SerendipUpdate's picture

The Story of Evolution, Spring 2005

Third Web Papers

On Serendip

The Enigma of the Incest Taboo

by AV

In Middlesex, Lefty and Desdemona fall in love as young adults after having been inseparable throughout childhood.

"Desdemona had always loved her brother as only a sister growing up on a mountain could love a brother ... Early on, the emotional sympathy she'd felt with Lefty had been so absolute that she'd sometimes forgotten they were separate people. As kids they'd scrabbled down the terraced mountainside like a four-legged, two-headed creature." (1)

They get married after being forced to flee from their home in Turkey, settle down in Detroit, have a child, and spend the rest of their lives happily married. Interestingly enough, although this can be a common scenario in fiction (two people who grew up together falling in love as adults), it is not at all common in real life. Although incest does occur in human society more often than it occurs in other animals (with a frequency of about 1%) (6) it rarely occurs in quite that manner.

Generally, when a brother and sister (or father and daughter, or mother and son) fall in love and get married, it occurs after they have spent most of their lives apart from each other. In particular, this kind of incest only occurs after the brother and sister have spent their childhoods separated from each other (in the case of sibling incest), or the child has spent its childhood away from the parent (in the case of parent/child incest).(6)

When incest occurs between family members who have never been separated in such a way, it generally takes the form of sexual abuse. It is rarely consensual, and is not a feature of a happy family (such as Lefty and Desdemona's) but of a severely dysfunctional one. Such incest is usually initiated by a family member who was himself abandoned and mistreated and physically abused in childhood (in the majority of cases the father or older brother), and often causes later serious psychological problems in the victim. (6)

There are of course exceptions. For instance, in Roman Egypt sibling marriage was quite common, accepted, and presumably consensual. (4)(9)Until the Middle Ages, the Zoroastrians practiced marriage between close-kin (xvélxvét) as a way of getting into Heaven and erasing mortal sin. (4)(9)However, the fact remains that incest is rare throughout the animal kingdom and remains a near-universal taboo in human societies.

The biological benefit of such a taboo is obvious. The benefits of sexual reproduction over asexual reproduction are erased by inbreeding. Inbreeding narrows the gene pool, reducing variety and therefore survival rates in a population. As it occurs between people with very similar genotypes, inbreeding can also cause the expression of harmful recessive mutations which might otherwise not have been expressed (such as Callie's 5-alpha reductase deficiency, in Middlesex). The progeny of incestuous relationships therefore have a higher mortality rate than normal. (5)

The incest taboo therefore helps prevent the negative effects of inbreeding, which are together called inbreeding depression. However, just as Desdemona in Middlesex was not aware of these negative effects, it is too much to expect that the incest taboo was purposely created due to some universal human awareness of inbreeding depression. It is especially too much to expect when one considers that incest (and particularly sexual abuse) is far more common in humans than in other animals, (6)to whom we cannot attribute such awareness.

So if the incest taboo does not arise from a conscious awareness of incest's negative effects, then where does it come from? Edward Westermarck developed a theory in the late 19th and early 20th century that tried to answer this question. He claimed that close contact with a person during childhood automatically creates an aversion towards sexual relations with them later in life. The incest taboo therefore does not act as a restraint against something which humans are naturally inclined to do in the first place. Rather,

"Generally speaking, there is a remarkable absence of erotic feelings between persons living very closely together from childhood. Nay more, in this, as in many other cases, sexual indifference is combined with the positive feeling of aversion when the act is thought of." (p. 80, 3)

He then goes further to say, "aversions which are generally felt readily lead to moral disapproval and prohibitory customs and laws," (p.84, 3) in an attempt to explain how the incest taboo could follow from such an aversion.

The tendency to develop such an aversion would be hereditary, and is paralleled in other animal species by their own inbreeding avoidance behavior. It would be an evolutionarily favourable trait since in general the people that we grow up with as children happen to also be close relatives. As a result, it would be a fairly safe guard against inbreeding. This sexual aversion would not be restricted to close relatives, though, but generalized towards anyone with whom one was in sufficiently close contact during childhood.

The fact that this sexual aversion can develop even towards non-relatives has been used to show that it actually exists as a factor in inbreeding avoidance, and not just as a by-product of the incest taboo. There is generally no taboo against marrying non-relatives that one has known since childhood. However, if one has grown up closely associated with these people, an aversion towards sexual contact with them will likely still develop.

There are two well-researched cases that demonstrate this phenomenon: one in Taiwan, and the other in Israel. In Taiwan, there was an old practice of arranged marriage where the sim-pua, or little bride, was raised in her future husband's household from a very young age. She and her future husband were raised almost like brother and sister, until the time when they had to abruptly become husband and wife as adults. There was no taboo against this sudden change in their relationship, of course. Rather, it was demanded of them. And it was often met with reluctance. The success of such marriages was significantly less than the success of other Taiwanese arranged marriages in which the future bride and groom met in adolescence. Marital success decreased proportionately with the decreasing age at which the girl met her future husband, beginning at ten and becoming especially low if they met when she was below the age of three. (8)

A more dramatic example was of children brought up in Israeli kibbutzim. Children brought up in the same peer group of the same kibbutzim, though unrelated to one another, were around each other as children more than they were around even their own parents. They did everything together from a very young age. And although they were not discouraged from marrying, very few who were raised together in such a way did. They claimed that they saw each other as siblings and could not think of each other in any other way. Those few who did marry had often first met sometime after the first six years of their life. In the cases where the two had met before the age of six, they had not been in continuous contact during that time. (2)

All of this implies that there is a critical period, sometime between infancy and the age of six or ten, during which time biological imprinting takes place which causes a later sexual aversion towards a person. Such imprinting would generally take place upon close relatives and prevent later inbreeding.

What of the incest taboo, then? Westermarck claimed that this sexual aversion resulted in the incest taboo. However, the connection between the two is still controversial. For instance, as I just described, such sexual aversion is not limited to close relatives. It is generalized towards anyone with whom one has been in close contact during childhood. The incest taboo, on the other hand, is far more specific, prohibiting sexual relations with close relatives in particular. If it is just a conscious manifestation of our innate aversion, why would there be this difference between the two? Perhaps we simply interpret our aversion as being directed towards relatives, since generally it is only directed towards relatives or ones whom we consider like relatives. As that is our personal interpretation of the aversion, the taboo becomes the same. (9)

But then, one might ask, why would one need a taboo against something which people are not inclined to do in the first place? We have a natural aversion towards starving to death, yet no one finds it morally repugnant when someone doesn't eat. Perhaps we need the taboo because there are cases where the sexual aversion does not develop properly, and further reinforcement in the form of a taboo is necessary to prevent incest. But in that case, how can you say that the incest taboo is a conscious manifestation of the sexual aversion? It may simply be a reinforcement, rather, which has co-evolved with this innate aversion.

Would such co-evolution be logical, though? Can cultural evolution parallel biological evolution in such an almost magically convenient fashion? The biological characteristic and the cultural taboo serve the same purpose: to prevent inbreeding. And yet while biological characteristics can be counted on to be hereditary, cultural evolution is a far more messy and unpredictable matter. The incest taboo is universal without having been genetically inherited, a mystery which would be conveniently solved if we could only say for sure that genetically inherited aversion has caused it.

These issues have not been resolved. The incest taboo remains something of a mystery. Much more is known about the development of sexual aversion towards childhood associations than about the incest taboo itself. It is fairly certain, though, to return to Middlesex, that in real life Lefty and Desdemona would either never have fallen in love or would not have remained so happily married. They grew up inseparable as children, and not in a dysfunctional family (so far as we know), so they would have developed a natural sexual aversion towards each other in adolescence. Such is fiction, though, and their love story is still a beautiful one. And it serves to conveniently maneuver the recessive genes for 5-alpha reductase deficiency syndrome into position so that Callie can turn out a hermaphrodite. Fiction is allowed to go places and tell stories that real life with its limitations cannot.


1) Eugenides, Jeffrey. Middlesex. (2002) Picador: New York, New York. (pp. 24-25)

2) Shepher, Joseph. Incest: A Biosocial View. (1983) Academic Press, Inc: New York, New York. (pp. 52-62, absence of intermarriage in the Israeli kibbutzim)

3) Westermarck, Edward. A Short History of Marriage. (1926) The Macmillan Company: New York, New York. (pp. 80-84)

from Wolf, Arthur P. and Durham, William H. Inbreeding, Incest, and the Incest Taboo: the state of knowledge at the turn of the century. (2005) Stanford University Press: Stanford, California.

4) Bateson, Patrick. "Inbreeding Avoidance and the Incest Taboos"

5) Bittles, Alan H. "Genetic Aspects of Inbreeding and Incest"

6) Erickson, Mark T. "Evolutionary Thought and the Current Clinical Understanding of Incest"

7) Wolf, Arthur P. "Explaining the Westermarck Effect, or, What Did Natural Selection Select For?"

8) Scheidel, Walter. "Ancient Egyptian Sibling Marriage and the Westermarck Effect"

9) Sesardic, Neven. "From Genes to Incest Taboos: The Crucial Step"



Comments made prior to 2007
in my personal viwe about marry between brother and sister should be allowed coz i saw many cases in egypt,turkey,and etc so many brother fall in love with his own(real)sisters , now days it very commen in muslims country also they make love with his own sister but cant marry???


frankly speeking i m also fall in love with my real older bro he is 34 and i want to marry with him but cant do it!!!! what should i do i dont understand ? i make love almost every day and sleep together actually i belong with rich family my parents live in usa and i live with my bro since last 4 years and we go out alone for shoping,picknic,cinemas,clubs,night clubs and drink together


i love my brother too much and i want to marry with him


plz plz try to remove this kind of obligations so that whos love with bro-sis they can marry each other at least not like me ? ... Nadia, 8 January 2007


stoney's picture

i can choose for myself

i think except for child molesters , everyone agrees that any for of incest with an adult and a child is disgusting and wrong . any sexual activity between any adult and any child is disgusting and wrong . that does not and should not have any bearing on what 2 consenting adults choose to do sexually should it ? of course people have an aversion to sexual attraction with family members . society tells us early on and often how wrong and disgusting it is . religion tells us it is a sin . somehow when children first become sexually curious it is often with a sibling that they explore with . it is not until after the adults tell them it is wrong that they think it is so . i am not a religious person . should i have to follow religious beliefs of right and wrong or morality ? of course not ! i choose for myself what is moral , and right and wrong . i am an adult , if my sister , or mother , or aunt or cousin wants to have a sexual relationship with me i believe i am fully capable of deciding for myself if i do or dont have sex with them . shouldnt all adults be able to choose this for themselves ? why should someone choose for me if it is wrong or right ? what would they make this determination based on ? their beliefs ? mine ? societies ? who decides what i can and can not decide for myself ? do i get to choose for someone else too ? this all seems a bit ridiculous to me . if it doesnt effect anyone else it is no ones business what someone else does . it definitely should not be against the law ......

Claudia's picture

I came from a very screwed up

I came from a very screwed up family. My mother was a stripper and my father was out of the picture before I was born. I have a half-brother who is a little less than two years older than me. My mother used to do crank all the time and would bring home men who would stay anywhere from one night to several years. Those relationships usually ended either in screaming fights, or when we moved. My brother was the one who made sure I was fed and did my homework. Our sleeping arrangements had been my sleeping in our mother's room on a twin air mattress while my brother usually slept on a hide-a-bed couch in the living room. When my mother brought home someone, I brought my bed next to my brother's. My brother had been a fairly deep sleeper and you could turn on the TV or radio without waking him, so you had to shake him to wake him up. When I was about 7, some of the men my mother lived with started molesting me. When I told her, she usually found some excuse to make it my fault. She caught one in the act and STILL blamed me. I think she was afraid of social services finding out and taking us away so she wouldn't be able to get benefits. I started sleeping in my brother's bed with him because he would wake up if one tried to do anything to me in the night because of all the commotion I would make and would start yelling. After a while, I couldn't get to sleep unless he was there next to me and almost never slept on the air mattress, even when there were no men around. One time, when our mother wasn't home, one of her boyfriends came for me while we were both sleeping and my brother and him started fighting. He beat my brother so badly that he nearly died. I think the guy already had the cops looking for him for other stuff, so he ran. Our mother blamed us again. After that, my brother got one of those mini baseball bats and slept with it.

When I was 11, I guess his hormones started kicking in because he started getting sexually aroused with me in bed with him. He wasn’t trying anything, but he was really tense and slept with his back towards me. I knew what was going on and figured it was just a matter of time before he was going to try something or tell me I couldn’t stay in his bed anymore. So I started sleeping on the air mattress again. Then one of my mother’s boyfriends tried something with me, which hadn’t happened in a while, and I got scared and started sleeping in his bed again. My mother had said to me several times that if you want a man in your life, you need to put out, so I figured that if I wanted my brother to protect me, I would have to start doing things sexually with him. To make a long story short, I started jerking him off, which eventually led to both of us performing oral on each other, then we started screwing when I was about 13. Did I like it? I guess I did sometimes. Better him than my mother’s boyfriends. At least he cared about me.

When I was 14, I found a boyfriend who was a biker and ran away with him. I never saw my mother or brother again. I did find someone several years later who knew both of us that said he heard from someone else that my brother had enlisted in the Navy, but was discharged early for some reason, but other than that, I’ve heard nothing else. I haven’t heard anything about my mother. I have a feeling she is probably dead.

A lot of bad things happened to me during those years after I left my family. Drugs, stripping, hooking, etc. I can only estimate the number of times I have been raped. I have been jailed for a lot of things and been 5150 a couple of times. I guess what I am trying to say is that although what my brother and I did wasn’t a good thing, I miss the feeling I had of being loved and protected by someone I know cared about me. Everyone else just used me. That’s screwed up isn’t it? My nicest memories are of my brother who I had sex with, who never hit me.

Daniel Lonsdale's picture


I agree with the belief that physical proximity to someone in childhood tends to inhibit sexual interest in them later on. It is widely reported that children who grow up together on Israeli kibutzes, although genetically unrelated, almost never form sexual unions later in life. I have, however, known several cases of siblings who openly admitted being attracted to one another. I doubt that any innate physical aversion exists preventing sex with close relatives. Why would someone not be attracted to someone who reminds them profoundly of themselves? And if procreation is all about passing on one's genes, then who better to do it with than a sibling who shares those genes? I suspect there would be a lot more casual incest were it not for the intense social stigma reflected upon incest couples.

lux's picture


you can do nothing when you fall in love or attracted from your soul sexually or emotionally with anyone be it your brother sister or daughter.our past is stone age where human had no social rules we were free as any other animals or birds.
If genetic problem is the only tention then a brother and sister or father and daughter can have sex using family planning medicine or condoms. sex makes people more close and when someone lovs someone they want to touch or have sex . sex is a right of any living being.

Diana's picture

I was 18 when I had sex with

I was 18 when I had sex with my cousin it was consensual and we both love it. We've been doing it nearly a year in our house or at their house just two blocks away. One afternoon my elder brother almost caught us kissing but when we got home my brother ask what we were doing. I made all sorts of excuses & he said he saw us french kissing. I denied at first & he said if I want I can all try it with him otherwise he'll tell our parents. I was curious with him and so we did. We were fondling & kissing all night. The next morning he sneaked into my room and we had sex for the very first time. We did it almost daily and there were times that we did it twice a day before sleeping & early morning just before our parents wakes for nearly two years. I was sexually active both with my cousin and brother but they don't know that I was having sex with both of them. I told my brother I lost my virginity by my former BF. I was about 21 when I stopped having sex with my cousin and 23 stopped having sex with my brother. But today we never talk about it and pretended that it never happened. My husband doesn't know my sexual experiences but whenever I'm in a family gathering with my husband, brother and cousin I'm always paranoid that they might tell my husband. I've been marriend to him for 11 years now & I don't want to lose him. Maybe it's a karma I don't have any kids and my brother as well he's been trying to have a child with his wife but seems unsuccessful. I don't regret of having sex with my cousin and brother but however I don't want it to happened again.

Sadie's picture

Are you for real?

This sounds quite tragic and sordid. I'm very sorry that you cannot conceive. I think you were at the age when sexual curiosity is at its peak so I do not condemn you if you were experimenting with your cousin and brother and that it lasted for years before you wised up and ended then. There must be some sort of emotional connection you felt with both and you expressed it through libidinal means. Sex became more exciting when it's forbidden, thatv much is true. Furthermore, even though incest is still considered a taboo in most cultures, I personally do not judge you since you seem to have recognize the disadvantage of your actions later on. I wish you have gotten over this so not to affect your marriage with your husband. It's quite upsetting when I think about it but thank you for sharing your story on the subject matter.