Is homosexuality unnatural?

[Larv]

Why do you presume such studies trying to eradicate homosexuality would be any different from trying to cure people from being "black," or curing asians from having more slanted eyes, or maybe "curing" people from having anything other than blond hair and blue eyes?...

Is it understood scientifically that homosexuality is equivalent to racial features like skin and eye pigmentation or hair color? I really don't think so. As such, while you intentions of tolerance are good, you're mixing apples with oranges. Homosexuality is more like left-handedness or any other condition that is not inherited genetically. There is no "gay gene" that I know of.

[sman]

Is it understood scientifically that homosexuality is equivalent to racial features like skin and eye pigmentation or hair color? I really don't think so.

 

I don't think so either, but we may be wrong. The way to find out is science, and science requires funding. It also requires caution and Inow's allusion to eugenics should be heeded.

So, duely warned, if homosexuality can be treated as an illness science can tell us, and if it can't, then science can enable us to unambiguously reject this ridiculous hypothesis.

It's also, I think, the best way to ensure quality of life for all persons. Maybe the best "cure" for homosexuality is nothing more than unanimous social institutions of acceptance and adoption. This is the trend society is taking and that is very uplifting, I just think that if there's more that we can do we should find out what it is.

[InfiniteNow]

Is it understood scientifically that homosexuality is equivalent to racial features like skin and eye pigmentation or hair color? I really don't think so. As such, while you intentions of tolerance are good, you're mixing apples with oranges. Homosexuality is more like left-handedness or any other condition that is not inherited genetically.

 

I would consider your criticism to be relevant if it had not already been addressed and shown to be invalid in this very thread. Since it's already been demonstrated conclusively that homosexuality has a genetic cause, your point can safely be disregarded.

 

 

http://hypography.com/forums/biology/17804-is-homosexuality-unnatural-11.html#post263920

[enorbet2]

If it weren't for simple prejudice against groups of people perceived to be different, and their subsequent persecution and suppression, this wouldn't even qualify as a question let alone a fairly long thread, let alone replete with all the emotional charge that often exists. It has already been pointed out, as if it had to be, that sex exists or is practiced by all sexual creatures for reasons other than procreation and the only reason to even characterize one kind as "natural" and another as "unnatural" is to prop up that prejudice. It is largely learned behaviour like any such baseless prejudice, beyond the mere arrogant and unsupportable assertion that "what I do is sex and what you do is perversion".

 

Any cursory look at genders, since they exist in a wonderful panoply in at least three separate arenas, all genetically produced not by a single gene but several that are turned either on or off in the womb, primarily through timing and intensity of the Mother's sex hormones in utero, renders even the concept of "same sex" ridiculously narrow minded. Gender is not binary nor is it identifiable solely by genitalia. Additionally the widespread occurrence of "prison gay" in which people engage in what passes for homosexuality with little or no social stigma and more often than not return to their previous orientation upon release, shows that any aversion is not only learned behaviour but easily suspended. So, in short, sexuality is programmed in our genes while hatred is taught. It can even be argued that from an evolutionary stance that the raison d'etre for sex itself is for diversity so the compulsion of some to oppress, exile, imprison, injure, lynch and on and on and on in an effort to create a completely homogenous tribe is counter evolutionary as well as just vile manners.

 

I've said it before in other threads and unfortunately I, and others, will likely have to say it for some time to come, that the human species will finally have made a quantum leap from coming down from the trees to cease all this petty bickering and focus on really important problems instead of making them up or blowing them way out of proportion (and No Beavis that is not a pun since "blow" is a figure of speech). It's as ridiculous and sad as Dr Seuss's butter-side up vs/ butter-side down warfare. It would be great to just move on, actually accepting the equality of all under the Law and in our hearts and minds.

[Larv]

I would consider your criticism to be relevant if it had not already been addressed and shown to be invalid in this very thread. Since it's already been demonstrated conclusively that homosexuality has a genetic cause, your point can safely be disregarded.

 

 

http://hypography.com/forums/biology/17804-is-homosexuality-unnatural-11.html#post263920

Sorry to prick your bubble, I-Now, but nothing you have provided here demonstrates anything conclusively about the causes of homosexuality. I think it is natural, just as left-handedness is natural, but you're turning the issue away from science and into a belief. Have faith, baby, and maybe everything will be OK. Meanwhile, let's get on with the science part.

[InfiniteNow]

Sorry to prick your bubble, I-Now, but nothing you have provided here demonstrates anything conclusively about the causes of homosexuality. I think it is natural, just as left-handedness is natural, but you're turning the issue away from science and into a belief. Have faith, baby, and maybe everything will be OK. Meanwhile, let's get on with the science part.

 

Sounds like a good plan. As per the reference I've now shared several times, here is a summary:

 

Whether or not a gay gene, a set of gay genes, or some other biological mechanism is ever found, one thing is clear: The environment a child grows up in has nothing to do with what makes most gay men gay. Two of the most convincing studies have proved conclusively that sexual orientation in men has a genetic cause.

 

William Reiner, a psychiatrist at the University of Oklahoma Health Sciences Center, explored the question of environmental influences on sexuality with a group that had been surgically shifted from boys to girls. These boys had been born with certain genital deformities; because it is easier to fashion a vagina than a penis, the boys were surgically made into girls at birth. In many cases they were raised as girls, kept in the dark about the surgery, and thought themselves female long into adulthood. Invariably, Reiner found that the faux females ended up being attracted to women. If societal nudging was what made men gay, at least one of these boys should have grown up to be attracted to men. There is no documented case of that happening.

 

The second study was an examination of twins by psychologist Michael Bailey of Northwestern University. Among identical twins, he found that if one was gay, the other had a 50 percent chance of also being gay. Among fraternal twins, who do not share the same DNA, there was only a 20 percent chance.

 

At first glance, those results seem to suggest that at least some homosexuality must not be genetic. Identical twins have the same genes, right? How could one turn out gay and the other not gay as often as 50 percent of the time? There are many other traits that are not always the same in identical twins, however, like eye color and fingerprints. The interesting question is, how do any of these major differences arise between two products of the same code?

 

The solution to that question is exactly what Bocklandt is trying to find. By looking not at DNA but at where DNA is switched off, he hopes to find the true genetic seat of homosexuality. Hamer looked at broad regions of chromosomes using genetic markers, a low-resolution result that tells little more than “something’s going on somewhere around here.” Bocklandt is hoping to look with a much stronger magnifying glass at the areas Hamer’s research *highlighted. If he succeeds, it will be a triumph not only for the genetics of homosexuality but also for genetic research in general.

 

Bocklandt has collected DNA from two groups of 15 pairs of identical twins. In one group, both twins are gay. In the second, one twin is gay, and the other is straight. Identical twins have the same DNA, but the activity of their genes isn’t necessarily the same. The reason is something called methylation.

 

 

And here is one of those studies referenced which demonstrates conclusively that homosexuality has a genetic cause:

 

 

A linkage between DNA markers on the X chromosome and male sexual orientation -- Hamer et al. 261 (5119): 321 -- Science

The role of genetics in male sexual orientation was investigated by pedigree and linkage analyses on 114 families of homosexual men. Increased rates of same-sex orientation were found in the maternal uncles and male cousins of these subjects, but not in their fathers or paternal relatives, suggesting the possibility of sex-linked transmission in a portion of the population. DNA linkage analysis of a selected group of 40 families in which there were two gay brothers and no indication of nonmaternal transmission revealed a correlation between homosexual orientation and the inheritance of polymorphic markers on the X chromosome in approximately 64 percent of the sib-pairs tested. The linkage to markers on Xq28, the subtelomeric region of the long arm of the sex chromosome, had a multipoint lod score of 4.0 (P = 10(-5), indicating a statistical confidence level of more than 99 percent that at least one subtype of male sexual orientation is genetically influenced.

 

And now a few additional studies which help to resolve the apparent "darwinian paradox" of how gayness can be genetically passed from one generation to the next, as well as others which support the genetic cause of homosexuality:

 

 

Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity ? Proceedings B

The Darwinian paradox of male homosexuality in humans is examined, i.e. if male homosexuality has a genetic component and homosexuals reproduce less than heterosexuals, then why is this trait maintained in the population? In a sample of 98 homosexual and 100 heterosexual men and their relatives (a total of over 4600 individuals), we found that female maternal relatives of homosexuals have higher fecundity than female maternal relatives of heterosexuals and that this difference is not found in female paternal relatives. The study confirms previous reports, in particular that homosexuals have more maternal than paternal male homosexual relatives, that homosexual males are more often later-born than first–born and that they have more older brothers than older sisters. We discuss the findings and their implications for current research on male homosexuality.

 

A genetic study of male sexual orientation

Homosexual male probands with monozygotic cotwins, dizygotic cotwins, or adoptive brothers were recruited using homophile publications. Sexual orientation of relatives was assessed either by asking relatives directly, or when this was impossible, asking the probands. Of the relatives whose sexual orientation could be rated, 52% (29/56) of monozygotic cotwins, 22% (12/54) of dizygotic cotwins, and 11% (6/57) of adoptive brothers were homosexual. Heritabilities were substantial under a wide range of assumptions about the population base rate of homosexuality and ascertainment bias

 

Familiality of female and male homosexuality

We examined data from a large cohort of homosexual and heterosexual females and males concerning their siblings' sexual orientations. As in previous studies, both male and female homosexuality were familial. Homosexual females had an excess of homosexual brothers compared to heteroxual subjects, thus providing evidence that similar familial factors influence both male and female homosexuality. Furthermore, despite the large sample size, homosexual females and males did not differ significantly from each other in their proportions of either homosexual sisters or homosexual brothers. Thus, results were most consistent with the possibility that similar familial factors influence male and female sexual orientation.

 

We also examined whether some parental influences comprised shared environmental effects on sexual orientation. Scales attempting to measure such influences failed to distinguish subjects with homosexual siblings from subjects with only heterosexual siblings and, thus, did not appear to measure shared environmental determinants of sexual orientation.

 

I mean, I can keep going if you really want me to. I'm curious why you're continuing to reject the genetic basis studies so greatly, without bothering to demonstrate where these studies are somehow flawed in either their methodology or conclusions. As seems abundantly clear to me, mine is the position with merit, and which is supported by the facts.

 

I'll say it again... The most convincing studies all show conclusively that homosexuality has a genetic cause. If you wish to suggest otherwise, then prove it.

 

 

Now, on a related note... If you still disagree with the genetic basis of our sexual orientation, perhaps you can tell everyone here precisely on what day you CHOSE to be heterosexual. That might be illuminating.

[Moontanman]

This thread has seemed do concentrate mostly on male homosexuality. Female homosexuals have been mentioned but by and large men seem to be both the point and the source of most problems with homosexuality in this thread and society. Not only do women seem to be more tolerant of male homosexuals women seem to be more likely to experiment with homosexuality as part of their sex lives than straight men or at the very least female humans seem to be more comfortable admitting to it as part of their sex lives in general. is female homosexuality different than male homosexuality in a basic way or it is different due to the influence of society?

[sman]

is female homosexuality different than male homosexuality in a basic way or it is different due to the influence of society?

 

Male and female sexuality is definately different. The old school of thinking that gender roles are compleatly socially constructed is just false. Male and females differ genetically, not only in the reproductive organs, but also in brain assembly. Male, for instance, seem to be aroused by the sight of nude females - pretty much indescriminately. Females(in general, of course) are not. All pornography is for men. (Playgirl obviously targets gay men, as the adds belie) Survey type studies show that men are much more likely to seek multiple partners, annonymous encounters...etc.

 

Male homosexuality is definately the most obvious of the two, and the most marked departure from experimental coitus, which is probably enough to explain much of what is labelled homosexual behavior. I think the prominence of male over female homosexuality is due to male sexual desires, instead of being counterpointed by female sexual desires, is being springboarded off of other male sexual desires.

 

Gay men that I've known have told me that if there had been a "choice" they would have chosen a normal life. They are repulsed by the thought of sex with women very similarly to me at the thought of sex with men. Lesbians that I've known havn't really displayed this barrier. Neither have straight women that I've known, for that matter.

[pamela]

Male, for instance, seem to be aroused by the sight of nude females - pretty much indescriminately. Females(in general, of course) are not. All pornography is for men. (Playgirl obviously targets gay men, as the adds belie)

excuse me? where do you get this information from? Women may be less verbal about expressing what arouses them, but that does not mean that they are not aroused by both nude men and women. Playgirl is for whomever chooses to read/view it. To assume that it is only for gay men is not accurate and only your speculation

Male homosexuality is definately the most obvious of the two, and the most marked departure from experimental coitus, which is probably enough to explain much of what is labelled homosexual behavior. I think the prominence of male over female homosexuality is due to male sexual desires, instead of being counterpointed by female sexual desires, is being springboarded off of other male sexual desires.

This really doesnt make any sense to me. Maybe it is most obvious to you because you are a male.

Gay men that I've known have told me that if there had been a "choice" they would have chosen a normal life. They are repulsed by the thought of sex with women very similarly to me at the thought of sex with men. Lesbians that I've known havn't really displayed this barrier. Neither have straight women that I've known, for that matter.

Sounds like your friends may have some unresolved issues, as all of us have- life is a learning process

I have a problem with your choice of the world normal. *sigh*

This thread has seemed do concentrate mostly on male homosexuality. Female homosexuals have been mentioned but by and large men seem to be both the point and the source of most problems with homosexuality in this thread and society. Not only do women seem to be more tolerant of male homosexuals women seem to be more likely to experiment with homosexuality as part of their sex lives than straight men or at the very least female humans seem to be more comfortable admitting to it as part of their sex lives in general. is female homosexuality different than male homosexuality in a basic way or it is different due to the influence of society?

It never occurred to me that this thread was targeted at males- it is concerning male and female homosexuality

maybe this will help you in the understanding of female homosexuality found in nature. To familiarize you, the terminology is tribadism

 

This position is not exclusive to humans. Females of the bonobo species, found in the Democratic Republic of the Congo, also engage in female-female genital sex, usually known as GG rubbing (genito-genital).

Tribadism - Wikipedia, the free encyclopedia

[enorbet2]

Some comments follow:

 

Hooray! MoonTanMans refined question redefines this thread as one of Nature vs/ Nurture and despite how badly that has been resolved among the general public, Science continues to progressively discover how much more we are defined by genetics rather than environment, desire, pressure, etc. Exemplary cases exist both in similarities and differences. Studies of twins separated at birth and raised by different families, even in different cultures, display stunning similarities.

 

It strikes me as oddly interesting that if one googles "epigenome" one of the first few hits is an article from Wired, titled "Whew! Your DNA Isn't Your Destiny". I think the "Whew!" displays the deep seated desire to believe we are captains of our souls, despite evidence to the contrary. Nature and Nurture are not altogether separate processes and are as intertwined as the double helix. It is only after environment is translated into compulsory genetics that characteristics are passed on, even trans-generational. Do we have choices? That seems fairly certain but not about our own biology and that includes gender. More on gender follows...

 

Male and female sexuality is definately different. The old school of thinking that gender roles are compleatly socially constructed is just false. Male and females differ genetically, not only in the reproductive organs, but also in brain assembly. Male, for instance, seem to be aroused by the sight of nude females - pretty much indescriminately. Females(in general, of course) are not. All pornography is for men. (Playgirl obviously targets gay men, as the adds belie) Survey type studies show that men are much more likely to seek multiple partners, annonymous encounters...etc.

 

sman, I think you are almost there but you seem to still hang on to a binary definition of gender where I see it as a continuum. Just because a person has one kind of genitalia does not imply that they have that same kind of brain or sexual preference. Example:

 

Male genitalia + male brain + hetero = one set

Male genitalia + male brain + homo/bi/whatever = another set(s)

Male genitalia + female brain + hetero (relative to body) = another set

>>>>>progression>>>>>

Female genitalia + female brain + hetero = another set

* Note - this progression is foreshortened as well as doesn't address genitalia blending which expands the progression considerably. Expanding variations on themes creates a progression list approaching infinity since like numbers we can always add one.

 

 

Male homosexuality is definately the most obvious of the two, and the most marked departure from experimental coitus, which is probably enough to explain much of what is labelled homosexual behavior. I think the prominence of male over female homosexuality is due to male sexual desires, instead of being counterpointed by female sexual desires, is being springboarded off of other male sexual desires.

 

What? Obvious to whom? What study shows even what is generally described as homosexuality as "experimental coitus"? relative prominence? This is entirely a subjective "conclusion" with no scientific support. It may be comfortable to oversimplify and pigeonhole but it isn't scientific. Females defined by males sounds utterly Victorian at best. Pompous and blind at worst. Certainly biased.

 

Gay men that I've known have told me that if there had been a "choice" they would have chosen a normal life. They are repulsed by the thought of sex with women very similarly to me at the thought of sex with men. Lesbians that I've known havn't really displayed this barrier. Neither have straight women that I've known, for that matter.

 

Normal? For statistics to have value the sample needs be large. Is it?

[lemit]

How about both natural and unnatural?

 

Natural, since it occurs in nature variously and is probably genetic, unnatural since it does not further the natural purpose of sex.

 

Does that make sense to anybody? I hope it does, since it has the potential to partially satisfy both sides or (more likely) make both sides hate me. As long as they do it equally, I guess I can handle that.

 

--lemit

 

p.s. No, I couldn't really handle that.

[InfiniteNow]

How about both natural and unnatural?

 

Natural, since it occurs in nature variously and is probably genetic, unnatural since it does not further the natural purpose of sex.

Would you be willing/able to define "natural purpose of sex?"

 

I ask because I'm sure you mean procreation, however, I think that displaces the true motivator for our sexual behaviors.

 

We have sex, quite simply, because it feels good. We don't tend to begin coitus thinking to ourselves, "Oh yeah... This is going to transfer my genes into a new generation!" We think, "This is gonna feel real good, and even better for you." It's really that simple.

 

 

We don't screw to procreate. We screw because we've evolved to enjoy it. When viewed rationally, we can all see that it is the enjoyment of sex itself... the pleasure we feel from it... which serves as the strongest motivator to copulate, procreate, and reproduce. Basically, the movement of genes forward into future generations is a side-effect of the decisions we make to seek pleasure... the decisions we make to have that orgasmic sensation... and it is the pleasure we feel from the act of sex itself which is what makes us do it to begin with.

 

Again, we have evolved to find the act of sex itself pleasurable, and finding pleasure in the act itself (not the outcome... not in the potential conception of offspring) results in the emergent property of us having non-procreative sex... it allows sex for fun to thrive... and finally, it allows some to find pleasure and preference when engaged in intercourse among same sex partners.

 

To say that only "procreative sex is natural" is to have a very myopic and biased view of the reality in which we exist, since our natural desire to seek pleasure is of a much higher priority than practically all else.

 

Case in point: We really like fellatio despite the fact that here is zero chance of procreation as a result of that act.

[Boerseun]

We have proven beyond any shadow of a doubt that homosexuality is normal. If we remove humans from our sample, and we only investigate those animals who don't exist in the human sphere, we've already listed thousands of species who engage in homosexuality for whatever reason.

 

Like INow says above, and I've said in my earlier posts, the motivator for engaging in sex is the orgasm. Animals are bribed to rub their genitals in such a way as to result in the discharge of sex cells. What they rub it against, is immaterial. As long as enough animals do it right, the species will carry on.

 

When we consider chimpanzees, sex becomes a tool ordering their social lives, establishing and strengthening bonds between individuals and the social hierarchy in general. The fact that it results in offspring is almost coincidental. Males hump each other to reinforce their standing on the social ladder. The humper is higher on the social ladder than the "humpee". And the "humpee" will then turn around and hump those lower on the ladder than him, thereby affirming his position. All perfectly natural.

 

Now that being the casel, if you want to discuss the genetic origins of homosexuality, I suggest you start a new thread. Because we have conclusively answered the question raised in the OP in this thread: Yes, homosexuality is normal. Next...

[lemit]

Would you be willing/able to define "natural purpose of sex?"

 

I ask because I'm sure you mean procreation, however, I think that displaces the true motivator for our sexual behaviors.

 

We have sex, quite simply, because it feels good. We don't tend to begin coitus thinking to ourselves, "Oh yeah... This is going to transfer my genes into a new generation!" We think, "This is gonna feel real good, and even better for you." It's really that simple.

 

 

We don't screw to procreate. We screw because we've evolved to enjoy it. When viewed rationally, we can all see that it is the enjoyment of sex itself... the pleasure we feel from it... which serves as the strongest motivator to copulate, procreate, and reproduce. Basically, the movement of genes forward into future generations is a side-effect of the decisions we make to seek pleasure... the decisions we make to have that orgasmic sensation... and it is the pleasure we feel from the act of sex itself which is what makes us do it to begin with.

 

Again, we have evolved to find the act of sex itself pleasurable, and finding pleasure in the act itself (not the outcome... not in the potential conception of offspring) results in the emergent property of us having non-procreative sex... it allows sex for fun to thrive... and finally, it allows some to find pleasure and preference when engaged in intercourse among same sex partners.

 

To say that only "procreative sex is natural" is to have a very myopic and biased view of the reality in which we exist, since our natural desire to seek pleasure is of a much higher priority than practically all else.

 

Case in point: We really like fellatio despite the fact that here is zero chance of procreation as a result of that act.

 

Yes, I agree. But I think the people on the other side of the argument are always going to feel kind of, well, icky even discussing homosexuality because they have been trained, practically since birth, to believe that it's just plain "unnatural."

 

I thought a long time before I put that first line on my signature.

 

I think the only way to really open a dialogue is to acknowledge that people really do believe that gay sex is "unnatural." I think people can work around that belief, but to refuse to admit that some people will need to do some work isn't productive. We don't need another closeted group.

 

I'm just trying to create a basis for negotiation. I'll probably fail and just make a lot of people angry with me. If the people on both sides if this divide could take their anger out on me and start to talk to each other, I'd be very happy.

 

--lemit

[InfiniteNow]

I'm just trying to create a basis for negotiation.

I don't so much want to negotiate. That's just me, though. It's not really my style. I want to decapitate my opponents in public and basically cut them out like a cancer. Then, when others see how epically these folks have failed at making an argument which is sound and meritorious, they will question their own thoughts and beliefs, and they will tend to naturally incline themselves toward my position.

 

More or less, that is.

 

I suppose negotiation is one approach, too.

 

 

 

I'll probably fail and just make a lot of people angry with me. If the people on both sides if this divide could take their anger out on me and start to talk to each other, I'd be very happy.

Your intentions are very noble, and also praise-worthy. In my desire to make you very happy, all I can say is, "Screw You!"

 

 

Hmmm... I still feel anger towards those who see homosexuality as unnatural. I may need to lash out at you a few more times to get the hang of this.

[Larv]

Sounds like a good plan. As per the reference I've now shared several times, here is a summary:

 

...

 

Now, on a related note... If you still disagree with the genetic basis of our sexual orientation, perhaps you can tell everyone here precisely on what day you CHOSE to be heterosexual. That might be illuminating.

All that is very nice, but wait. You said "it's already been demonstrated conclusively that homosexuality has a genetic cause..." While I also think homosexuality has a genetic cause, at least for males, I do not believe that it has been "demonstrated conclusively." The difference between us is only your assertion that a genetic cause of homosexuality has be "demonstrated conclusively." If so then show me the genes.

[InfiniteNow]

All that is very nice, but wait. You said "it's already been demonstrated conclusively that homosexuality has a genetic cause..." While I also think homosexuality has a genetic cause, at least for males, I do not believe that it has been "demonstrated conclusively." The difference between us is only your assertion that a genetic cause of homosexuality has be "demonstrated conclusively." If so then show me the genes.

 

One need not know specifically "which genes" are responsible in order to demonstrate the responsibility of genes themselves.

 

That's the larger point, and you're now moving the goal posts. I did adequately demonstrate conclusively that genes are responsible. Asking about which specific genes are responsible is a separate question entirely.

 

 

However, on that specific point, this seems to be one of the more useful studies:

 

 

http://tigger.uic.edu/~bmustans/Mustanski_etal_2005.pdf

This study reports results from the first full genome scan for male sexual orientation. Using 73 previously reported families and 73 new families with two or more gay male siblings, we found three new regions of genetic interest. Our strongest finding was on 7q36 with a combined mlod score of 3.45 and equal contribution from maternal and paternal allele transmission. This score falls just short of Lander and Kruglyaks (1995) criteria for genomewide significance. Several interesting candidate genes map to this region of chromosome 7. Vasoactive intestinal peptide (VIP) receptor type 2 (VIPR2; MIM 601970) is a G protein-coupled receptor that activates adenylate cyclase in response to VIP (Metwali et al. 1996), which functions as a neurotransmitter and as a neuroendocrine hormone. VIPR2 is essential for the development of the hypothalamic suprachiasmatic nucleus in mice (Harmar et al. 2002), which makes it an interesting candidate gene for sexual orientation in view of earlier reports of an enlarged suprachiasmatic nucleus in homosexual men (Swaab and Hofman 1990). Sonic hedgehog (SHH; MIM 600725) plays an essential role in patterning the early embryo, including hemisphere separation (Roessler et al. 1996) and left to right asymmetry (Tsukui et al. 1999). Homosexual men and women show a significant increase in non-righthandedness, which is related to brain asymmetry (Lalumiere et al. 2000).

 

Two additional regions approached the criteria for suggestive linkage. The region near 8p12 contains several interesting candidate genes, given the hypothesized relationship between prenatal hormones and sexual orientation (Mustanski et al. 2002). Gonadotropinreleasing hormone 1 (GNRH1; MIM 152760) stimulates both the synthesis and release of luteinizing hormone and follicle-stimulating hormone, which are important regulators of steroidogenesis in the gonads, and inhibits the release of prolactin (Adelman et al. 1986). GnRH is synthesized in the arcuate nucleus and other nuclei of the hypothalamus (Kawakami et al. 1975). Steroidogenic acute regulatory protein (STAR; MIM 600617) mediates pregnenolone synthesis and is involved in the hypothalamic-pituitary regulation of adrenal steroid production (Sugawara et al. 1995), which in turn plays an important role in sexual development. Neuregulin1 (NRG1; MIM 142445) produces a variety of isoforms that regulate the growth and differentiation of neuronal and glial cells through interaction with ERBB receptors (Burden and Yarden 1997; Wen et al. 1994).

 

The 10q26 region is of special interest because it results from excess sharing of maternal but not paternal alleles. Previous studies have suggested that there is an excess of homosexual family members related to the proband through the mother, and we have proposed previously that this might result in part from genomic imprinting (Bocklandt and Hamer 2003). In support of a connection between 10q26 and imprinting, a germline differentially methylated region has been identified at this location by Strichman-Almashanu et al. (2002) who performed a genomewide screen for normally methylated CpG islands and found 12 regions to be differentially methylated in uniparental tissues of germline origin, i.e., hydatidiform moles (paternal origin) and complete ovarian teratomas (maternal origin). Such CpG islands can regulate the expression of imprinted genes over distances of several hundred kilobases. The region around the 10q26 CpG islands includes the brain-expressed gene Shadow of Prion Protein (SPRN), several transcription regulators (ZNF511, VENTX2; MIM 607158), neurotransmitter interacting proteins (DRD1IP; MIM 604647), and cell signaling pathway proteins (INPP5A; MIM 600106, GPR123).

 

Four previous linkage studies have been conducted on the X chromosome and together produce a statistically suggestive MSP in the Xq28 region (Sanders and Dawood 2003). Because the focus of this study was a full genome scan with the ABI linkage mapping set on a partially new set of families, we began by reporting results for these markers on the full sample. This analysis did not produce evidence of linkage in the Xq28 region; therefore, we conducted supplemental analyses to clarify this result given previous findings. Our first supplemental analysis combined results from the two previous reports from our group (Hamer et al. 1993; Hu et al. 1995) in order to determine the magnitude of the linkage signal in the 73 previously reported families that currently comprised half of the current sample. This produced a mlod of 6.47. To determine whether the lack of linkage evidence in the full sample was attributable to the new markers or the additional families (who were not selected based on family transmission patterns), we then conducted analyses on the previously reported families by using the markers from the ABI linkage mapping set. This produced an mlod score of 1.99. Table 2, which provides a summary of the single point and multipoint results for this comparison, suggests that the difference in mlod score between the restricted sample with the old and new markers is attributable to the non-optimal position and density of the new markers. The difference in mlod scores between the full sample and the sample restricted to families without evidence of paternal transmission (with the goal of enriching the sample for families showing maternal transmission) denotes the possibility of etiologic heterogeneity for the proposed Xq28 locus.