ONTD Political

Scientists claim to have solved the 'evolutionary riddle of homosexuality'

10:46 pm - 12/12/2012
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.

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.

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."


OP: Heard this on tonight's news and thought I would share.
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mastadge 13th-Dec-2012 04:39 pm (UTC)
How apropos that I read this on the same day that I read about how epigentic effects may have become more overstated than justified by the evidence. Anyway. I've only ever studied bio at introductory levels so my understanding of DNA methylation and so forth is insufficient to comment further on all of this. I wonder how well this model can cope with a whole spectrum of human sexuality rather than just the basic binary mentioned here, though.
evilnel 13th-Dec-2012 04:46 pm (UTC)
I wonder how well this model can cope with a whole spectrum of human sexuality rather than just the basic binary mentioned here, though.

That is a very interesting question. My guess is that there is still environmental interaction (and interaction with other gene sets we're not yet aware of), which often determines how genes express. For example, many mental illnesses have a genetic link, but aside from having a parent with mental illness, exposure to certain kinds of viruses, presence of trauma, and general environment can have an effect on whether or not such things ever manifest. But I'm not a biologist (my background is in experimental psych) so this is just a thought. Good question, though!

Edit: I just realized I used mental illness as a comparison--this is in no way a comment on homosexuality as a mental illness, it was just the first example of biological/environmental interaction that I thought of!

Edited at 2012-12-13 05:04 pm (UTC)
evilnel 13th-Dec-2012 04:47 pm (UTC)
I hope they can gather some more support for this theory. I think that strong evidence might be able to silence some of those annoying 'homosexuality is a choice!' people. We can hope, anyway!
fluffydragon 13th-Dec-2012 04:53 pm (UTC)
People won't 'believe in' global warming, many will never accept that homosexuality isn't a choice. One study or five hundred won't change that.

Silence? no. Educate. It's a long hard road, but minds can be changed over time, and studies won't do it.
thecityofdis 13th-Dec-2012 04:48 pm (UTC)
this smells like bullshit.
darth_eldritch 13th-Dec-2012 05:07 pm (UTC)
popehippo 13th-Dec-2012 05:22 pm (UTC)
I... am really unnerved by this because I don't think this is going to silent people who try to fix gay people by telling us it's a choice or that we were abused as kids or something. They'll just try to say "well this is just proof that you're deficient and sick".

Also does this even remotely approach the idea of bi/pan folks? Or all the talk of fetuses being masculinized/feminized, what the hell do they think about femme lesbians or butch gay guys?

Yeah, I kinda smell bullshit.
darth_eldritch 13th-Dec-2012 05:34 pm (UTC)
Yep. This to everything you say.
sashafarce 13th-Dec-2012 05:40 pm (UTC)
I find this fascinating even if it just provides fodder for the rightwingnuts. I have a lesbian sister on my dad's side. (I'm also a lesbian, just so that doesn't come out sounding creepy.)
romp 14th-Dec-2012 06:26 am (UTC)
you have a lesbian half-sister?

I'm amazed when parents get more than one queer kid. It's like winning the queer lottery. (I love my straight kids but would have loved to share a culture with a kid)
keeperofthekeys 13th-Dec-2012 05:48 pm (UTC)
The paper can be found here for those interested in reading. I recommend getting a cup of coffee; it's 27 pages long.
intrikate88 13th-Dec-2012 06:02 pm (UTC)
LOL, I was just coming here to offer the paper for those who don't have JSTOR access.
thenakedcat 13th-Dec-2012 06:34 pm (UTC)

Ever since I first heard about epigenetics, it seemed to offer a better explanation for the diversity of sexuality and gender expression than the older "sexually antagonistic" explanation for homosexuality (i.e., that gay men may be less likely to reproduce with a woman but their female relatives with the same trait are more likely, thereby cancelling out the Darwinian effect and retaining the trait in the population at a low level). Epigenetics also begins to explain the phenomena of female homosexuality, which sexual antagonism never accounted for.

For those here who dislike the implication that "masculinization" or "femininization" are connected to sexuality as well as to gender expression, note that the article says that several different locations on the genome are implicated. That helps to explain phenomena like bisexuality and the Kinsey scale (because some people are going to have more genes activated than others) but it also implies that anatomical sex, sexuality, and gender identity are all coded separately That lines up with the experienced reality of straight cis people, straight trans people, queer cis people, and queer trans people.

Edited for unintentional sentence fragment.

Edited at 2012-12-13 06:35 pm (UTC)
moljn 13th-Dec-2012 06:42 pm (UTC)
gay men may be less likely to reproduce with a woman but their female relatives with the same trait are more likely,

Now THAT'S evolution! ;-)

Edited at 2012-12-13 06:43 pm (UTC)
(no subject) - Anonymous
lady_borg 13th-Dec-2012 11:12 pm (UTC)
Yeah same.
bnmc2005 13th-Dec-2012 07:49 pm (UTC)
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.

Maybe there is more to this study than what we see her but I don't know enough science to not read a political motive in this.... I'm just side-eyeing all the references to "masculinization" and "feminization" ... it seems to rely on the same old trope that gay men must be feminine and women must be masculine AND the idea that gender itself is binary AND the erasure of bisexuality.

teacup_werewolf 13th-Dec-2012 08:53 pm (UTC)
And gender-fluidly
angelofdeath275 13th-Dec-2012 08:37 pm (UTC)
So tired of this bs

Why is it always something that MAKES someone gay</p>

Never talks about what makes one hetero for one

And always leaves other orientations out

teacup_werewolf 13th-Dec-2012 09:00 pm (UTC)

I can understand what they are getting at, but I am kinda tired of the idea that things that are complex and diverse like genetics and sexuality, can be explained with one cause or reason. What part of "spectrum" do you all get? Gender/sexuality is multi-variable complex. It's not something that has one cause or one link to the other it's nebulous and vast. Masculinity and Femininity are human constructs. They were made for our social structure. Those binaries cause a lot inconsistencies and erase a other gender labels and orientations. Personally I sick and tired of this dichotomy of "Male/Female" brains or genes or whatever it's bullshit.
oudeteron 13th-Dec-2012 09:23 pm (UTC)
Thank you.

I personally would love to see the positivist notion of "there is one reality and we are going to find the universal cause of it even if we have to invent it from scratch" finally lose the uncritical acceptance it still has. Like, these scientists are working with constructs whether they're ready to admit it or not, and yet it's all being treated as "objective fact" because the words science and genetics are involved.

And cue more gatekeeping as soon as they do figure out a way to incorporate this breathtaking new discovery into practice. Like hell any of these people actually care about making a breakthrough for our sake. Nope, it's always the straight cisnormative ~curiosity~ that's the true factor of legitimacy.
mingemonster 13th-Dec-2012 09:27 pm (UTC)
Meh. I don't really see the point of this. It won't change how people see us, it won't change how we're treated. The people who think we're pedos or sinners aren't going to like us just because nature made us that way. I feel like this is a lot like autism research, where so much time and money is spent on finding the cause of it but there's not enough research that could actually help autistic people
teacup_werewolf 13th-Dec-2012 09:40 pm (UTC)
Ugh you have no idea. I have been doing activism for the autistic community for years, people rally for 'cure' and so little is done to prepare for this generation of autistics and having stable services.
lafinjack 14th-Dec-2012 12:55 am (UTC)
natyanayaki 14th-Dec-2012 05:08 am (UTC)
I love that!
halfshellvenus 14th-Dec-2012 01:24 am (UTC)
I don't know why people go on and on about finding the "homosexuality gene," unless they're the people that will suddenly think abortion is a GOOD thing if a baby might have that gene.

We haven't found a gene for left-handedness either, and probably never will. But that does not mean it isn't both biological and naturally occurring, much in exactly the same way as one's sexuality.

Not everything biological has a gene marker.
lastrega 14th-Dec-2012 07:58 am (UTC)
This is in no way a settled explanation, and I was reading an interesting discussion on this over here at The Conversation.
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