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Why It’s Gross To Kiss Your Sister

“Researchers who wanted to find out why it is not only taboo to kiss your sister, but also disgusting, said on Wednesday they have discovered why in a discovery that challenges some basic tenets of Freudian theory… Cosmides and her colleagues tested 600 volunteers, asking them all sorts of questions jumbled together so they would not know what was being studied… they asked about all sorts of ethical dilemmas, including questions about sexual relationships with siblings. Among the volunteers were people who had never shared a home with their siblings — for instance, full- or half-siblings born 10 or even 20 years apart. What determined incest disgust and altruism was the same — how much time an older sibling spent watching his or her mother care for a younger one, or how much time the two spent together in the same household. ‘If you co-resided with them for a long time as a child, you’d treat them as you’d treat any full sibling. This seems to operate non-consciously,’ Cosmides said. Especially strong was the effect of watching one’s mother care for a younger child. ‘They would be very altruistic toward that baby and they’d be grossed out at the idea of sex with that baby as an adult,’ Cosmides said… The study contradicts the teachings of Sigmund Freud, who described Oedipal urges and conflicts, Cosmides said. ‘He thought you are attracted to your relatives and your siblings and parents and it takes the force of culture and society to keep you from committing the incest that is in your heart,’ she said. Cosmides said Freud had a possible reason for his own feelings — he had a wet nurse who cuddled and breastfed him: ‘Who their brain thinks is mom is different from who they consciously believe is mom. For them it is quite reasonable that they have an attraction to their mothers.’” — Yahoo (US)

On one hand, this seems like a no-brainer result. Basically it amounts to the fact that the more time you spend with someone, the less sexually appealing they become. Old married couples know this. And siblings share that “familiarity breeds contempt” quality with long married couples. In most cases, they know each other too well to find each other attractive. (It’s interesting to note that, in the comments on Genetic Sexual Attraction Syndrome, many “sufferers” didn’t live with their siblings when they were young.)

On the other hand, to simplify this research to such a level is unfair. Professor Leda Cosmides and her collaborator John Tooby are pioneers in the field of evolutionary psychology, and if you read some their actual research on incest avoidance you find insight after insight. For example, their work seems to give a biological foundation to the notion that opposites attract: “when it comes to a choice between two alternative mates, the less related mate will produce fitter offspring: kinship should be antierotic. As a result, selection is expected to have shaped adaptations that govern mate attractiveness so that less related individual will seem more attractive than more related individuals, other things being equal. Of course, when the choice is between mating with a relative, and not mating at all, selection would favor mating.” No doubt this is why many people are attracted to exotic men or women: they may not realize it, but exotic mates promise better babies.

Another interesting point — and one which seems to jive with the landscape of perversion — is that women have a greater incentive to avoid incestuous behavior than men. A woman can only have a baby once a year or so, thus she has a very strong evolutionary motivation to avoid any behavior such as incest which might produce an unhealthy child. Conversely, a man is almost unlimited in his (potential) fathering opportunities, and thus he risks little by engaging in couplings that might produce unhealthy offspring. And of course this all has psychological ramifications. For example, evolution provides a material basis for the feelings engendered by rape:

This is a tragic fact about the selection pressures that are likely to have shaped human sexual psychology, and may provide the explanation for certain patterns of abuse. For example, among our ancestors the fitness payoffs for a man of inseminating a woman who has only a 50% chance of being his daughter could have easily been positive. For the possible daughter, however, any substantial chance that a potential fertilizer is her biological father leads to a strongly negative average payoff, and her psychology should be selected to experience such a possibility as horrifying.

It would be interesting to see to what extent the exceptions — the perverts who practice incest — confirm or deny these findings, particularly since the subjects involved in the research seem to have been “normal” in the first place. Also, it’s hard not to wonder how these evolutionary impulses hold up today, when the imperative to reproduce has lost its punch (see the declining birth rates in industrialized countries) and when people are aware that they can divorce the pleasure of sex from the necessity of reproducing. Does evolutionary psychology pertain to people who fuck just for fun? Are these people mutations? Or is everyone really just a sexual automaton powered by a primal impulse to perpetuate the species?

Comments Total: 15
William Thirteen
Feb 21 2007
5:32 pm

regarding the theory of ‘familiarity breeding contempt’ – we have a current court case here in germany regarding a fellow and his sister who were raised apart, later met and have since not only engaged in incest but have reproduced – four times!,2144,2356730,00.html

the article also notes that there are no laws against incest in France, Belgium, the Netherlands, Portugal, Turkey, Japan, Argentina or Brazil!

Feb 24 2007
8:58 am

yuk incest is just wrong even if you don’t grow up with your sibling it’s wrong to have sex with them and reproduce inbred handicapped children that sociaty will have to pay for in rehab and hospital visits. it’s socially unacceptable and breaks up any combination of the natural family unit.
the above link tells it all.

Feb 25 2007
4:34 pm


MISS-Understood to ladycara
Feb 26 2007
12:25 pm

GSA is an extremely delicate and sensitive issue. Unless you experience it first hand, you could never possibly understand it. Please don’t label it. You have no idea how it consumes your entire life. Sorry to tell you this… but it’s all around you and has been for a very long time. I’m glad that it’s existance is finally being revealed to the world.
What about those of us who’ve found true love? Do we not deserve to be happy as well? Or should we be confined to a life of unhappy marriages, misery, and suicidal tendencies because we might be “hurting” someone? Do you not think that we might be hurting too? What about those of us who suffered as a result of other people’s (namely our own birth parents) selfishness for many years?
You know… there is always two sides to every story. Maybe (just maybe) some of us in GSA relationships are 100 times better off than we ever were before.
To be perfectly honest, I’m getting fed up with everybodys self-rightous opinions. There are many other social and world issues that far out-weigh being in love with someone that “society” doesn’t accept.
There’s only one “judge” that we need to worry about… sorry, you’re not Him.

Mar 1 2007
11:10 pm

reply to miss-understood: i have a cousin that is the product of a GSA relationship between a father/daughter pairing and that child is riddled with cystic fibrosis we don’t (thats the whole family or their past friends ) talk to them any more they should have known better then to have a child when that illness obviously runs in the family, they made their bed and now come to us looking for money so they can treat their sick child and they have another of these sick children on the way,it’s not fair that i feel i have to give my uncle and first cousin money so they can treat their “love child” only to find out she is having another one, yes much to my families disgust i have given them money to help them out, but that was under the condition they do not have any more. now i don’t feel i should be understanding about this subject. one mistake or failure of birth control in my eyes is forgivable but it happening a second time is just plain wrong. and to all those who say i should help with their child well i have and i did but i don’t think it’s healthy to enable them to just keep having sick children.

MISS-Understood to ladycara
Mar 2 2007
5:49 pm

Yes… I agree that it is very irresponsible of those people to have children knowing full well that the illness is already a genetic defect within the family unit.
I’m sorry for the family members that are “guilted” out of money to help care for the child, and I’m sorry for the child and his/her parents suffering as a result of this disorder.
Did you know that children born out of “directly related” parents typically only suffer from birth defects when they come from a long-line of inter-related parents? (That is – several generations). Most children born from related parents are perfectly normal. Any couple (related or not) who choose to pro-create knowing full well that the chance of birth defects are high should be prepared for the risk involved.
This unfortunate child may still have suffered from the genetic defect even if the father/mother were not related.
I’m sure that the parents have alot of love to offer to the child as well as each other.

Apr 26 2007
9:28 pm

To ladycara
Well..what do you say to all the women who choose to have children with downs syndrome and other handicaps that have nothing to do with incestuous relationships? There are millions of babies in ICU and costing insurance companies and taxpayers money to take care of their handicapped disfigured you have a valid point to that..or is that okay? Maybe you should make an informed opinion rather than an ignorant misinformed opinion..I know people who have children with their relative and they are perfectly healthy children? Personally I think being gay or lesbian is nasty let alone being in an interracial relationship…but guess what..loving my brother is a love that you can never have…I know he is always going to be there. The love that you dreamed of as a little girl is the life I am you know for a fact that your man is going to be there for the rest of your life? No you dont but I do. I am very proud of what I am doing which is why we went on Primetime Tv..and are planning more interviews. I dont believe society can stop at GSA since they already allow every other sexual taboo to be accepted..personally not everyone agrees with these type of relationships but society as whole society as a whole cannot stop at the others which were once taboo.

Apr 26 2007
9:28 pm

Whats up misunderstood? mail me its been a minute since we’ve talked

Jun 13 2007
9:05 am

Hey Rachael I saw you on that TV special with Barbara! I only wish it was longer.

The findings of the study really make sense to me. I grew up in a different home then my half sister and although we are not in a relationship, we have both been very attracted to each other.

Jul 14 2007
6:40 pm

I’m sorry it took me so long to reply to this post..I will check back sooner. As for me and Sean..we will be celebrating 8 years together this Oct. Still very happy and very much into each other. Although this doesnt work for everyone. I have a large network of friends that I have met b4 and after the show..and I have seen a lot of heartache. I think for some reason God has given us a wonderful each other. And we really do pray together every day.Good luck with the relationship that you do have with your hs and please know that your not perverts for the attraction that you have. Take care and write back if you please.

Aug 23 2007
12:10 am

Hey Rachael,
My Half-sister and I Just watched the ABC Primetime special. You have no idea how releaving it was to hear that we are not alone. My Half-sister(Who I do not think of as that) and I were seperated at a very young age and didn’t meet again for 22 years. When we meet, it was love at first sight. We’ve been together for 2 years now, but have had to keep it a seceret from the world. We thought we were alone, but now know that we are not. On the primetime special, it mentioned that there are some internet sites that are societies of people with the same GSA as you and I both share, and you also mentioned that you have other friends with this same GSA. Could you please let me know how to get to these websites? We would very much like to meet and talk to other people who share the same problems dealing with society. Thank You for you time. W.M.

Nov 12 2007
12:03 pm

I met my paternal half-brother when I was 46 and he was 50. The love was overwhelming. He was right in front of my face all the time, and I could think of nothing else. He felt the same about me. We have been living together for four years now, sharing a house as brother and sister. What happens within the walls of the house is our business. For the record, I have the usual “icky” reaction to the idea of sex with any of my adoptive brothers, with whom I was raised. Please note there is no physical reason I could not have had children with one of my adoptive brothers … we would not have had a higher incidence of defective children because we’re related on paper only. From this I have learned the taboo, the gut reaction to sibling sex, is learned by living together while we grow up. It doesn’t exist when we are raised apart. He’s not in front of my face all the time now, but he’s never far away. The love is deeper, and we need each other as much as we did the day we met. For the first time in my life I feel complete.

Rob Moth
Dec 11 2007
1:26 pm

I understand your position with respect to non-blood siblings and seperation. In my case (and maybe I am twisted) my sister and I were involved in some experimentation which did not involve penetration of any kind. It was at least on my part purely a deep bond that we had together which over a long time enabled us to be together in a sexual way, satisfying our need. Upon reflection I had no disgust but maybe some guilt or concern that we would be discovered. I had no problems personally with kissing my sister, it only heightened my sexual tension. My sister on the other hand was fine with mutual experimentation or masturbation. We kissed but she felt a bit weirded out by it but gave me the opportunity on occasion. When we talk here about GSA I don’t feel that i have any abhorence with respect to my attraction to my sister and to this day even though we stopped the games 25 years ago, she does not hate me, quite the contrary. So in a nutshell our experience was not negative, it was mutually positive.I have been happily married for over 19 or more years to my wife and feel quite responsible and normal within society. The only area that I differ is that I have an attraction to my sister that is very different than that with my own wife. Maybe I should be a case study?

Jul 24 2008
9:56 pm

Until yestrerday I didn’t even know this had a name.Sure every body is different but true love is so hard to find.I say if you find it hold on to it.

Feb 22 2009
11:57 pm

ladycara nothing like my drunk 75 yo mother sucking my cock smoking a cigarett getting me hard so i can stick it up her asshole butt fuck my mother

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