Which sex act do lesbians love most?

Homo, sex and DNANews about same-sex love

The importance of the Xq28 region has recently been confirmed, but only as a factor in a far more complex process. There is now a colorful bouquet of new theories. After that, the focus of desire is likely to be decided in the womb. Genes play a role, but above all their control, epigenetics. A biological finding that is being considered in politics, at least in the USA. Science in focus asks how desire finds its direction.



When the blood runs inside me like this
I feel that in my limbs
Lusts that are mad and blind
I want to dance with the brothers.

Friberg: "According to the theory of evolution, traits that reduce the number of children should be very rare. Homosexuality definitely belongs in this category. Nevertheless, homosexuality is amazingly common in people. That is an evolutionary puzzle."

That death would come in sleep
And take me into the dark
that I never see the day again
because in my soul are
Things i don't understand
(Armin T. Wegner)

Ulrich: "The causes have always played a major role in the history of lesbians and gays, because homophobia and transphobia were legitimized with the charge of being unnatural and therefore to be rejected in principle. Interestingly, the causes of heterosexuality were never asked about."

Men and women have sex. In every constellation. Anywhere in the world and at any time. But not all love is equal before the law and society.

"I'm gay myself. I always wanted to know why am I who I am? Why do I like what I like? What makes me different from other people?"

Tuck Ngun is from Malaysia. Tolerance is not necessarily a top priority there. When he saw a film about the gay district of San Francisco as a child, he knew: that's where I want to go. Today, at the age of 31, he lives in Los Angeles. He is researching a yeast protein: solid science. But when he had to determine the topic of his doctoral thesis, he decided to look at this one aspect of his private life through the eyes of a scientist: his sexual orientation.

"Part of that was because of this notion, especially prevalent in the US, that if there is a biological basis, that behavior is more acceptable. Because then it's not your fault."

Tuck Ngun, checked shirt, side parting, looks more down-to-earth. Scientifically, he is taking a risk: Not only is he choosing a sensitive field of research, he is also using an exciting new approach: epigenetics.

"Ok, we think biology plays a role in sexual orientation, but there's nothing specific about genes. So our idea was, maybe it's about controlling genes and DNA."

Crunchy Frankfurters &
Juicy hamburgers
Sweet Berliners &
Crispy cobbler boys
Skin clean, friends!
The butchers are on our side
And the bakers
(Detlev Meyer)

Two to three percent of women and three to four percent of men only love representatives of their own gender. Certainly a minority, but a minority that occurs all over the world and is therefore normal. Psychological theories have blamed absent fathers or dominant mothers in the 20th century. There are hundreds of studies that have tried to substantiate these theses.

"None of the studies found any classic socialization pattern, and certainly no pattern that showed that bringing up someone would become homosexual or heterosexual. That tends to speak in favor of biological assumptions."

Parents and educators obviously do not play a major role, according to Hartmut Bosinski, sexual medicine specialist from Kiel. During his time as a professor at the university, he dealt intensively with homosexuality and is familiar with the studies.

"Contrary to popular belief, a homosexual orientation is not limited to humans. Rather, there are certainly animal species. The most beautiful example are the sheep, where seven percent of rams are gay, and preferentially if they have access to females the male. "

But what exactly does biology mean here? When it comes to sexuality, researchers quickly think of hormones. The gay rams, for example, probably received too little male testosterone in the womb and therefore show a more feminine behavior. There is also some evidence of hormonal changes in gay men and, more clearly, in lesbian women. But it is also clear: the hormones do not explain everything. Another astonishing finding: homosexual men have a particularly large number of older brothers. This is also an indication of biology, because stepbrothers or adoptive brothers have just as little influence on sexual orientation as older sisters.

"It goes so far as to say: Every older brother increases - statistically mind you! - the probability that the younger one becomes homosexual by 33 percent. In other words, purely statistically, 13 percent of all homosexual men would attribute their homosexuality to the fact can, statistically, have more older brothers. "

This well-documented finding shows that the decisive course is set before birth. Maybe even at the time of conception. The nineties are the years of the human genome project. No wonder researchers are now turning their attention from hormones to genes.

"I would say the biggest breakthrough in this field was made by Dean Hamer."

Tuck Ngun (31) studied sexual orientation as part of his doctoral thesis (Allen Lipson)

For Tuck Ngun, Dean Hamer is a hero. Hamer had noticed that gay men often had gay uncles on the maternal side of the family. If there were genes for homosexuality, then they should be inherited through the maternal X chromosome. At the US National Cancer Research Institute in Bethesda, Dean Hamer compared the X chromosomes of gay brothers in 1993.

"We discovered that there was a connection between homosexuality and a region called Xq28. Gay pairs of brothers mostly had the same version of that region while their heterosexual brothers had a different version."

Xq28 is a long stretch of the X chromosome, densely packed with many genes. To this day, nobody knows exactly which of these effects what in terms of homosexuality.

"Maybe it just has something to do with the metabolism. Or the gene affects a sexual center in the brain. Or it has an even more indirect effect. It could make people care less about the opinions of others. when we have the gene. "

Dean Hamer never claimed to have found "the homogeneous". Still, the American gay movement in particular was enthusiastic. "Xq28 - Thanks Mom", "Xq28 - Thanks Mom" ​​was featured on many T-shirts.

Hamer: "I don't think that our result influences how gay men see themselves. They know there is no choice here, that naturally arises early in life. But especially in the USA there are many people with prejudices about homosexuals, they consider it a conscious decision, a sin, bad, directed against society. If they understand that this is not true, that homosexuality has much deeper roots, that it is innate, then it will hopefully change their attitude in a good direction. "

Dean Hamer's findings are more than 20 years old. The geneticists were very hardworking, the studies got bigger and bigger. In addition to Xq28, regions on chromosomes seven, eight and ten are now also associated with homosexuality.

Ngun: "There were some interesting findings, but the direct link: this mutation leads to the result that is still missing for sexual orientation."

Probably because there is no such thing as "homogeneous".

Math teacher draw
About Turkish prostitutes
Concentric circles and
Expect the worst
Philosophy professors
Leave the superstructure and
Throw on your stomach
On the golden ground
Of the craft
Only the gas station attendants are
Satisfied with their own kind
And love their colleagues
(Detlev Meyer)

Hormones and genes don't decide everything

Genes aren't everything, hormones are part of the story, the number of brothers is just another finding. Tuck Ngun is looking for an interface where the different pieces of the puzzle fit together:

"Identical twins have the same DNA, but their sexual orientation is not always the same."

It has recently become clear that very different melodies can be played on the same genetic keyboard. Every human cell has the same genes. But a different subset of these genes is active in each cell. Markings on the DNA determine which are permanently switched off or permanently active. In this way they determine the identity of the cells and give them a kind of costume for the role of their life. The key word is epigeneticism.

Ngun: "I imagine epigenetics is a kind of dimmer: it can increase or decrease the activity of genes."

Is this also where the root of the sexual orientation lies?

Tuck Ngun is moving to the Center for Gender-Based Biology in Los Angeles. There he studies how hormone levels in the womb affect the control of the genome of unborn mice. Around the same time, a trio of researchers from the United States and Sweden published a theoretical model on the connection between epigenetics and homosexuality. They start where a fetus sets the course towards female or male.

In male fetuses, at a very early stage in development, a gene on the Y chromosome is responsible for the formation of the testicles and thus for the production of a large amount of testosterone. This male hormone then organizes the formation of a male body and brain. If this gene does not exist, little testosterone is produced and a female body and a female brain develop.

"Our model is based on the observation that testosterone alone cannot explain sex development because the hormone levels of male and female fetuses seem to overlap."

Urban Friberg, co-developer of the new model from the university in Linköping, Sweden. Testosterone levels, he concludes, are not in themselves a clear signal. There are female fetuses with fairly high testosterone levels and male fetuses with comparatively low levels. But how do the cells then know whether to start the female or male development program? Friberg:

"So we suggested that sexual development be stabilized through epigenetic effects."

Epigenetics, so the idea, should work in a kind of feedback loop: a first testosterone surge sets markers, so it uses epigenetics to ensure that the cells react more sensitively to the hormone. Subsequent fluctuations in testosterone levels can then no longer disrupt the development. Whatever happens, a man emerges. In female fetuses it is the other way round, their cells are becoming less and less sensitive to testosterone, so that they are clearly heading in the direction of women.

Friberg: "Normally these epimarks are erased between generations. But sometimes this erasure is not complete. No problem if the epimarks match the gender of the child. But if, for example, a mother passes on her feminine epimarks to a son, then his development can be Steer towards homosexuality. "

The hormone signal is the same as in other male fetuses. But it is interpreted differently by some cells. Part of the brain develops according to the female pattern and so many years later the desire is directed towards men. Conversely, if the father's male epimarkings accidentally reach the daughter. Then your cells become overly sensitive to the little testosterone and this directs part of the development in more male paths. And maybe this woman will later love other women. Tuck Ngun finds the approach very plausible.

"With epigenetics, small differences in the environment in the womb can lead to differences in the control of genes and later in life to differences in behavior. Regardless of whether it is homosexuality or something else."

Two female traffic light men shone for the CSD 2015 in Munich. (picture alliance / dpa / Sven Hoppe)

Urban Friberg and his two colleagues' model can explain a multitude of variants of gender identity and desire. But in the end it's just that: a theoretical model. It hangs in the air, so to speak.

In his mouse experiments, Tuck Nugn found the first indications of epigenetic markings. But mice are not humans. And so he and his colleagues are looking for a more direct route to the epigenetics of human homosexuality. In 2013 they started a twin study

"We studied 40 pairs of identical twins. One of the brothers was gay, the other straight. First we determined the pattern of a certain epigenetic marker, namely DNA methylation. And then we told a computer program, OK, that is two groups of people, can you tell them apart by DNA methylation? "

Nobody knows if something like this is even possible. There are millions of methylation sites in the genome, the team is focusing on 140,000 of them. A computer program developed by Tuck Ngun called "Fuzzy Forrest" - initially works with the data of 20 pairs of brothers and finally identifies five epigenetic markings that could have something to do with sexual orientation. Two of them are actually in genes that affect the brain. That sounds plausible. But when so many places in the genome are examined, you can quickly find something plausible. Therefore, Tuck Ngun asks his program to predict which of the brothers will love men among the remaining couples.

"Our algorithm was able to predict sexual orientation 67 percent of the time. That's a lot better than if it had guessed. But of course it's not perfect, OK?"

It was about pairs of brothers who knew one of them was gay. Predicting whether or not any man is gay is a different challenge altogether. Nevertheless, there are headlines again about an alleged homosexual genetic test. The criticism after the publication in 2015 is fierce, but less in official scientific channels and more on Twitter. Tuck Ngun is the first to admit that this is more of a pilot study than solid evidence.

"Clearly, we examined far too few people. But that's because of the funding. In the US in particular, it's practically impossible to get money for studies on sexuality, unless it's about diseases. So we really have that." Made the best of what was possible under the circumstances. "

Many question marks, especially with regard to cause and effect. Do these five epigenetic markers play a role in the genesis of homosexuality? Or is it the other way around, and certain life circumstances of gay men lead to the changes? Whatever the answer, theoretician Urban Friberg can now, for the first time, access concrete data.

"This study shows that epigenetics is involved in homosexuality. But it is still too early to say whether Ngun's findings really fit our model or whether there are other epigenetic mechanisms."

An epigenetic model could answer one question in any case: Why homosexuality persists in evolution, even though gay men rarely father children. Friberg:

"There are costs of homosexuality and evolution definitely registers that. But they are negligible compared to the advantages. The same epigenetic mechanisms stabilize the sexual development of men and women."

A study from Italy even shows that in families of gay men there are more children on the maternal side - an evolutionary advantage, believes Hartmut Bosinski:

"So these epigenetic research approaches are extremely exciting. They explain the interaction between the environment and the plant."

Everything made of leather
But by the way
You are like everyone
In the same way
The hair on the chest is only a sham.
And do you scream with pleasure
Yes then I fall asleep.
Drink your milk friend
howl out
And did you cry
then come home!
(Rainer Werner Fassbinder)

The role of the sexes

"So until recently the assumption had always been that gay men had to have a particularly large number of female hormones, that the brains of gay men looked more like women's than men's, and vice versa, of course, in women the same way mixed up two things in a very unscientific way that initially have nothing to do with each other. The gender identity as I said - I feel like a woman or a man - initially has nothing to do with which person I love. "

Lieselotte Mahler from the Berlin Charité heads the section "Sexual Orientations and Identities in Psychiatry and Psychotherapy" of the medical association DGPPN. The variety of sexual desires and ideas is great. Among the gay men there are the tough leather guys who rather exude an excess of masculinity, just like the feminine queens. Lesbians and, incidentally, also heterosexuals show an equally broad diversification.

"Women are more flexible compared to men. Lesbian and heterosexual women have a greater variation in what they desire or can imagine. While men are much more exclusive, i.e. exclusively heterosexual or exclusively homosexual."

Regardless of the role played by genes, their epigenetic control or hormones, biology seems to keep male sexuality in narrower tracks. Women, on the other hand, seem to have more leeway. The American developmental psychologist Lisa Diamond from the University of Utha calls her sexuality fluid, ready to change when a suitable counterpart appears. Sex medicine specialist Hartmut Bosinski does not want to rule out that different rules of the game may apply here for the sexes.

"In view of the fact that the sexual development of heterosexual men and heterosexual women is in large parts fundamentally different, it would be wrong to assume that it should now be different for homosexual men and homosexual women."

Seen in this way, a gay man is above all a man who only orientates himself differently in one area, his desires. But this one area is under close scrutiny in many societies. Therefore the study of the biology of homosexuality always had a political component.

Homosexuality. (picture alliance / Jose Jacome)

It was not until 1990 that the World Health Organization removed the diagnosis of homosexuality from the catalog of mental illnesses. In the USA, but also in Germany, religious groups continue to offer therapies for the alleged disease homosexuality. In the spring of 2016, the Psychiatric Society of Indonesia specifically recommended such treatments.

Mahler: "This is why this World Medical Association position paper was important, which we were able to adopt in 2013, where it became clear that loving the same sex is part of normal human sexual orientation diversity, and that every type of therapy has negative consequences. So people become depressed, suicidal when trying, which is doomed to fail per se, and that it is not justifiable from an ethical point of view. "

Enlightenment is needed. And here facts can definitely make a difference, says Hartmut Bosinski.

"It has been shown, for example, that people who are informed about the biological predisposition of sexual orientation and have the information that sexual orientation is not a question of choice, that they are less homophobic, that is, show less rejection of homosexuals."

Real hatred of homosexuals, on the other hand, can hardly be influenced, according to Markus Ulrich from the Lesbian and Gay Association in Germany. Basically, he is happy that geneticists have so far had little concrete to offer. Because if a biological basis were really identified, then prejudices could become effective in completely different ways.

"Ask handicapped associations how they stand, so to speak, about all these genetic tests before the birth, there is also massive, yes, a great danger. Or all of the abortion rates of girls in certain countries, which are clearly based on social stereotypes, on social ones Hierarchies and power structures are based, and so it cannot be ruled out that they are not reproduced even to lesbians and gays just because there is now a homo gene. "

That would not even be a misuse of research results. Ulrich thinks: Even the scientists' gaze is distorted.

"They always formulate these theories very clearly as a deviation. So that something was not properly deleted in the mother's DNA and that is why people are gay. Something has always gone wrong. And that is exactly the characteristic of homophobia, that there is a deficit is, it is not equivalent, it is a deficit and biological explanations do not necessarily make up for that. "

No gay person suffers pain, no lesbian dies from their love. Seen in this light, the question arises why so much research is being carried out at all. Lieselotte Mahler is not at all surprised: The interest will remain, she says, as long as the question: Homo or hetero? still play a role in our societies. It was no different with left-handedness. When left-handers were considered sick and were forcibly re-educated, money flowed into research.

"Now in a world where right- and left-handedness is no longer assessed, you're either right-handed or left-handed, and there are enough materials, scissors, etc. for left-handed people too, research into the causes has faded into the background. It's just like that one would say, "Should we research why someone becomes straight?" is also not really in the interest.

The soul speaks to the body: You have won!
Meat no longer resists, it triumphs.
Call me unscrupulous, I tell everyone:
Only with love do I stand and have to fall.
(William Shakespeare, translated by Christa Schuenke)

Science and politics

Tuck Ngun wanted to better understand his own homosexuality. That there would be so much ado about his study made him pensive. Even his new approach to same-sex love did not lead to more tolerance or unity: On the contrary: his finding became part of a political debate in which knowledge plays a secondary role at best. For this reason, too, Tuck Ngun left the research field. He now works in his own data analysis software company. And his private life is that again: private.

"It just wasn't that important to me anymore whether there was a biological explanation of sexual orientation. Little by little, I realized that it didn't matter. Regardless of whether it was about sexual orientation or gender identity or some other characteristic. Her moral worth shouldn't depend on whether she's innate, and then it's okay. It depends on whether you're a good person, gay, straight, or transgender, so people should accept you, not your genetics or anything else. "