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Scientists claim to have solved the ‘evolutionary riddle of homosexuality’

Wednesday, December 12, 2012

A group of scientists say they possibly have solved the question of what makes a human being gay, according to a study published Tuesday by the National Institute for Mathematical and Biological Synthesis (NIMBioS).

According to the study, published online in The Quarterly Review of Biology, “Epigenetics” – how gene expression is regulated by temporary switches, called “epi-marks” – appears to be a critical and overlooked factor contributing to the long-standing puzzle of why homosexuality occurs.

Drs. Bill Rice of the University of California Santa Barbara (left) and Urban Friberg of Uppsala University.
Photo via NIMBioS.

The team, led by University Of California Santa Barbara’s Dr. William Rice and Dr. Urban Friberg from the Uppsala University in Sweden, found that gay people get that trait from their opposite-sex parents: a lesbian will almost always get the trait from her father, while a gay man will get the trait from his mother.

Sex-specific epi-marks, which normally do not pass between generations and are thus “erased,” can lead to homosexuality when they escape erasure and are transmitted from father to daughter or mother to son.

From an evolutionary standpoint, homosexuality is a trait that would not be expected to develop and persist in the face of Darwinian natural selection. Homosexuality is nevertheless common for men and women in most cultures. Previous studies have shown that homosexuality runs in families, leading most researchers to presume a genetic underpinning of sexual preference. However, no major gene for homosexuality has been found despite numerous studies searching for a genetic connection.

In the current study, researchers from the Working Group on Intragenomic Conflict at the National Institute for Mathematical and Biological Synthesis (NIMBioS) integrated evolutionary theory with recent advances in the molecular regulation of gene expression and androgen-dependent sexual development to produce a biological and mathematical model that delineates the role of epigenetics in homosexuality.

Epi-marks constitute an extra layer of information attached to our genes’ backbones that regulates their expression. While genes hold the instructions, epi-marks direct how those instructions are carried out – when, where and how much a gene is expressed during development. Epi-marks are usually produced anew each generation, but recent evidence demonstrates that they sometimes carryover between generations and thus can contribute to similarity among relatives, resembling the effect of shared genes.

According to the study, sex-specific epi-marks produced in early fetal development protect each sex from the substantial natural variation in testosterone that occurs during later fetal development. Sex-specific epi-marks stop girl fetuses from being masculinized when they experience atypically high testosterone, and vice versa for boy fetuses.

Different epi-marks protect different sex-specific traits from being masculinized or feminized – some affect the genitals, others sexual identity, and yet others affect “sexual partner preference.” However, when these epi-marks are transmitted across generations from fathers to daughters or mothers to sons, “they may cause reversed effects, such as the feminization of some traits in sons, such as sexual preference, and similarly a partial masculinization of daughters,” according to the study.

The study purports to solve the evolutionary riddle of homosexuality, finding that “sexually antagonistic” epi-marks, which normally protect parents from natural variation in sex hormone levels during fetal development, sometimes carryover across generations and cause homosexuality in opposite-sex offspring. The mathematical modeling demonstrates that genes coding for these epi-marks can easily spread in the population because they always increase the fitness of the parent but only rarely escape erasure and reduce fitness in offspring.

Sergey Gavrilets, NIMBioS’ associate director for scientific activities and the study’s co-author noted, “Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality.”

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38 more reader comments:

  1. I would say. Their is nothing to solve. I was born Gay. And I now know who I am, what I am about. And where I am happy to be at. With my brother’s and sister’s LGBT people’s.. t.c. Fred M.

    Posted on Wednesday, December 12, 2012 at 7:27pm
  2. here’s my scientific evaluation of homosexuality, it is what it is.

    Posted on Wednesday, December 12, 2012 at 7:29pm
  3. Always have to know the “cause” so they can try and fix it. I wish they would go after blue eyes or something.

    Posted on Wednesday, December 12, 2012 at 7:31pm
  4. scientists have discovered the devil?

    Posted on Wednesday, December 12, 2012 at 7:37pm
  5. Aren’t scientists supposed to working on something like a cure for cancer or a cure for AIDS or you know, something that actually matters?

    Posted on Wednesday, December 12, 2012 at 7:37pm
  6. And you see ladies and gentleman… this is exactly what our taxes go to….. :/

    Posted on Wednesday, December 12, 2012 at 7:54pm
  7. And again a theory that tries to mold human development to darwinian standards. As you can see from our varied ethnic development, we are fluid animals. This study is just as valid as the theory that finger length determines sexuality….ie not at all. How about realizing that if you have to try to keep proving heteronormativity, then it probably doesnt exist. Stop trying to get funding by appearing political and do some disease/fuel management already.

    Posted on Wednesday, December 12, 2012 at 7:55pm
  8. HA, I knew it was my mother’s fault!

    Posted on Wednesday, December 12, 2012 at 8:07pm
  9. If only they’d start looking for the bigot gene.

    Posted on Wednesday, December 12, 2012 at 8:09pm
  10. I am excited by this news. I know some people can use knowledge in a stupid way, as already demonstrated, but why we are who we are is fascinating. The moral issues come later. Sexuality does not make us immoral, as we all know. Some ignorant people might try to use this against us. However, their use of how or where our sexuality comes from will not change their awful opinions of us. We just have to let them know genetics are as much to blame for sexuality as it is for the sex of the child or the color of their eyes. Big deal. However, the science is interesting!

    Posted on Wednesday, December 12, 2012 at 8:17pm
  11. as I read the article one thing kept coming to mind . . .the concepts of eugenics. MOVING ON !

    Posted on Wednesday, December 12, 2012 at 8:20pm
  12. Shall I point out if we claim our sexuality is genetic it will come from mom or dad no matter how you try to spin it? Come on people, take a science class.

    Posted on Wednesday, December 12, 2012 at 8:28pm
  13. Unless you want to say we chose this…>:(

    Posted on Wednesday, December 12, 2012 at 8:28pm
  14. They should be trying to figure out a way to fix us any day now. Maybe the money that went into this “research” could have been sent to the thousands of queer youth who are currently homeless?

    Posted on Wednesday, December 12, 2012 at 8:28pm
  15. Ok…let’s start working on a cure….for religious bigotry.

    Posted on Wednesday, December 12, 2012 at 8:29pm
  16. Why do we waste money on junk science?

    Posted on Wednesday, December 12, 2012 at 8:30pm
  17. Man you guys make me feel awful about the LGBT community.

    Posted on Wednesday, December 12, 2012 at 8:34pm
  18. I don’t know what a good number of these words mean.

    Posted on Wednesday, December 12, 2012 at 8:37pm
  19. 1) This was a computer model. It didn’t prove anything, it says, given the assumptions the authors made, the math is feasible. 2) This was a computer model, so the amount of money spent to do this likely wasn’t overwhelming, it was probably a side project to begin with. If we actually tried to confirm this it would be expensive. 3) After hearing a talk by one of the authors on monogamy evolution, I would have to be convinced heavily by this paper that the model wasn’t built on extreme cultural biases. 4) Most of the people doing this kind of work don’t want to “cure” us, they want to use this as tools against the fundies. Yes, it might not work as well as they want, but they aren’t trying to bring back eugenics (which Wright disproved anyway, due to population genetics).

    Posted on Wednesday, December 12, 2012 at 8:44pm
  20. That makes sense to me, but there seems to be a little cultural bias in the interpretation of the evidence

    Posted on Wednesday, December 12, 2012 at 8:57pm
  21. (scoffs) There no way to solve gays because won’t work it!!!! God is only judge on us, Period! whatever to scientist peoples!

    Posted on Wednesday, December 12, 2012 at 9:18pm
  22. all is they slow i new that ages ago… but that doesnt mean they need a cur

    Posted on Wednesday, December 12, 2012 at 9:30pm
  23. I don’t like the way this is being presented and why we need to be studied. It feels like watching XMEN. We are treated as aliens and studied how our wonderful characters are formed. There are other very important things that needs our attention.

    Posted on Wednesday, December 12, 2012 at 9:31pm
  24. all i got from this was that they proved -yes we are born this way- other then that its just silly to be wasting time and money on studies like this.

    Posted on Wednesday, December 12, 2012 at 9:45pm
  25. Its not a sexual “preference.” Its what/who we are attracted to. There is no choice in the attraction. So how can it be a preference? As a Gay man I can honestly say that I have never once in 44 years of life been sexually attracted to any woman, ever. Hence how can it be a “preference?”

    Posted on Wednesday, December 12, 2012 at 9:47pm
  26. “The” reason? There is more than 1 reason you brilliant idiot scientists.

    Posted on Wednesday, December 12, 2012 at 10:20pm
  27. While this study does support my personal belief that I was born gay, just as many others were born straight, I am exercising caution before jumping the gun on this and advise all those who come across this article to do the same. This was
    one study and one result does not make something definite. So many more studies must be done and so many more questions must be asked, addressed and answered. I myself plan to research numerous scientific terms used in this article to fully be able to offer an educated opinion. So please, read this with a questioning mind :-)

    Posted on Wednesday, December 12, 2012 at 10:21pm
  28. Hey, I tried to post a comment on the on this article, but “something went wrong” was the message I received and it wouldn’t let me post it. I don’t know if it’s a webpage glitch or whether I have to be a member or something else, so I am just going to post it here for now and try again tomorrow… Of course your thoughts/opinions/suggestions are welcome too

    I am a heterosexual, but I share your passion for science and we are all brothers and sisters in the human species so I wanted to provide y’all with some more information that science has provided for us.

    In 1995, Zhou et al. found that the bed nucleus of the stria terminalis was larger in males and females; however, male-to-female (identified themselves as females in a males body) transsexuals showed to be very similar to that of a females, whereas homosexual males were more similar to heterosexual males. When the study was replicated in 2000 by Kruijver et al., they found that male-to-female (identified themselves as males trapped in a females body) was within the size range of that in a heterosexual male’s brain. In other words, there was strong evidence to suggest that the size of the stria terminalis was related to the individual’s sexual identity (not orientation).

    In 2004, Roselli et al. discovered (in domestic sheep) a sexually dimorphic nucleus in the medial preoptic/anterior hypothalamic area was significantly larger in rams than the ewes. This nucleus was also twice as large in female- oriented (heterosexual) rams than it was for male-oriented rams.

    So to sum up what these studies have found is that there are IN FACT physiologic, measurable differences in certain regions of the brains. Unfortunately, this research is still a long ways from drawing solid conclusions, but it is definitely suggesting that biology plays a huge role in a person’s sexual identity and/or orientation. This information was taken from “Physiology of Behavior” textbook, 10th edition, written by Neil R. Carlson. There is more information on these topics if anyone is interested or would like to share the info.

    PS. I know that the word “preference” is easy to be misinterpreted by those that want to condemn you, but I personally know some people that it is their choice and I find that to be perfectly okay. It’s everyone’s right, whether there is biological influence or not. I realize it’s perhaps easier for someone in my position to say this, but my hope is that the LGBT community will “own” that choice as a human right as well, rather than let the other side use it as leverage. Stay united, stay strong, and don’t worry too much about the other side, they’ve already lost. They just haven’t realized it yet I LOVE YOU ALL!! Take care.

    Posted on Wednesday, December 12, 2012 at 10:26pm
  29. ^ Darron Perry

    Posted on Wednesday, December 12, 2012 at 10:27pm
  30. lol woot… Thanks Sarah!!

    Posted on Wednesday, December 12, 2012 at 10:29pm
  31. what crap!

    Posted on Wednesday, December 12, 2012 at 10:40pm
  32. all I can say is bullshit!!!!!!!!!

    Posted on Thursday, December 13, 2012 at 12:18am
  33. when will they solve the “evolutionary riddle of heterosexuality”?

    Posted on Thursday, December 13, 2012 at 2:49am
  34. ho

    Posted on Thursday, December 13, 2012 at 3:30am
  35. Boring… It is obvious to me, that is is Natures way of saying “WHOA! To many of your kind! Stop reproducing!”

    Posted on Thursday, December 13, 2012 at 4:28am
  36. I do not believe that this has been subject to multiple experiments and proper peer review. It just is not good science.

    Posted on Thursday, December 13, 2012 at 6:17am
  37. But what about lipstick lesbians? I’m happy to hear of the research, but saddened by the continued usage of negative verbiage about lgbtq folk.

    Posted on Thursday, December 13, 2012 at 6:59am
  38. what about people who are truely bisexual how does that fit in to this theory

    Posted on Thursday, December 13, 2012 at 9:46am