First post; be gentle, Teeming Millions. The Master declined to address the following. Twice. I understand given the volume of mail. Many in the gay community (&GLBT), including several friends of mine, posit that heredity dictates why/how they have the orientation they do. I can’t bring myself to ask them, (out of politeness), how this could be, if genetics cannot be passed through single-sex unions. In theory, no passage of these genes is possible, excepting the (fairly) rare cases of artificial insemination/donation. Random occurances? Any studies? Any geneticists out there to clarify? Thanks for any enlightenment.
The science literature in the last few years has mentioned a possible gay gene. I’m too lazy to search for any cites now. Feel free to do so. Several ways that gay genes may be inherited. Gays can, and do, have sex with the opposite sex. The gene may be recessive. Also, and this is what I remember from my readings, the gene is not dispositive of the sexual tendency. It’s a factor that may induce homosexuality if conjoined with environmental factors.
If genetic, it could be one of those phenomena that only occus with certain combinations of otherwise neutral (or other-functional) genes, or only when both copies of a certain variant of a certain gene (or set of genes) are present.
I think the jury is still out on exactly how a person becomes gay, but an interesting statistic is that out of identical twins, if one twin is gay, the other twin has a 50 percent chance of also being gay. This hints at a genetic factor being involved, and also indicates that its not just genetics. If it was purely genetic, then the number would be 100 percent. If it was purely non-genetic, the number would be significantly less than 50 percent.
Your concept that the gay gene cannot be inherited is flawed for several reasons.
First of all, if it exists at all, it probably gives one gay tendencies, or the potential to be gay. It wouldn’t neccessarily make someone with the gene full blown homosexual.
Secondly, society has been rather intolerant of gays. They have frequently had relationships with the opposite sex, even though they aren’t naturally inclined that way. Oscar wilde, for instance, was married and had children. so, the gay gene would still be likely to pass down the generations.
The reduced fecundity concern is definitely a mark against keeping “gay genes” in the pool. There’s the olde “Kin Selection” argument, where gay relatives provide sufficient benefit to their heterosexual brothers, cousins, etc. that the genes can remain in the population. There’s also the possibility that it’s a result of a set of genes, each of which is sufficiently beneficial to outweigh the lower number of offspring if one has the whole set.
It’s my opinion that it’s simpler to stick to developmental arguments… maternal/fetal hormone exposure or something similar. So everyone had the potential to be born gay, they just didn’t get the right cocktail of environmental stress while they were developing.
There is a theory that gayness has percisted because it is a survival trait for the species. If a family includes a man or woman who never marries, never has kids, that person can be a sort of “extra parent” for his or her neices and nephews. A family that includes one of these extra adults has an edge over families that don’t.
Im not sure this theory is plausible, however. It seems to me that in most past eras, pretty much everyone who lived long enough to do so, became a parent, regardless of orientation. (Not that they had our modern conept of orientation.) So if there are such things as “gay genes” they would have been passed on.
And since the current concepts of gay and straight developed, I think gay people have often become parents. As far as I know, being gay does not mean that one cannot have sex with the op sex. Closeted gays often married and had children. Uncloseted gays who want children often manage to have them. So again, if there are such things as “gay genes” they can be passed on.
Mangetout raised one of the key genetic issues here – it’s entirely possible to donate a gene for a trait without demonstrating that trait. Many genes are active only when an individual possesses two copies (recessive genes); but this overly simplistic type of genetics doesn’t reflect the reality of more complex genes. Many genes require another gene, which may not do anything on its own, to be present in order to have an effect.
From the studies I’ve seen involving pairs of identical twins, the fact that one twin in a pair is gay does not necessitate that the other is, but the likelihood is increased. This would tend to indicate that it’s not entirely genetic, but also not entirely non-genetic.
Further speculation into the cause of homosexuality is likely to be opinion-based and at great danger of being wrong. For example, the ‘hormonal influences during early life’ theory includes, at its core, the belief that people with homosexual orientations are less male or female than heterosexuals. Psychological theories, such as the belief that gay men cannot form ‘normal’ same-sex relationships because of distant fathers or not playing enough football, are generally arrived at from a highly biased system of beliefs and cannot possibly explain how all, or even most, non-heterosexuals came to be that way.
The real cause, I think, will eventually be seen to be largely genetic with a psychological component. It may also be that humans have an innately more clouded sexual orientation than has long been thought. Bonobos, one of the primate species most closely related to humans, are pansexual – they engage in not-for-reproduction sexual activity and both male and female same-sex activity. To my knowledge, nothing is known on whether humans may be similar, and to speculate on what the implications might be if they were would involve too much opinion for this forum.
I should note that, since my training is in biological chemistry, my views on the genetic basis of homosexuality is clouded by the Central Dogma of Molecular Biology – since I can’t think of any way that sexual orientation would be determined by a protein or a chemical reaction, I can’t say that it clearly must be genetic.
In many species only one male or one female member of a group of individuals provides genetic tissue for an entire generation. In those species, the tendency of the social behavior to remain the same continues, even though the donating individual has the overwhelming influence over heredity for the entire group. It is not the case that a predilection for non procreation cannot be inherited. It is an observable fact and the regular pattern among wolves, and many other types of animals.
Obviously this subject is more complex than a single gene which determines who is gay, and who is not.
Tris
People have covered the arguments quite nicely already, but a few additional points:
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There is nothing that says that a gay person cannot engage in reproductive sex; it’s just that they’re not motivated to form heterosexual unions for the purpose. Our own Homebrew and his ex-wife, both gay people, have a wonderful little boy, the product of their union before they came out to each other and the world.
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My own hypothesis is that homosexual orientation may well be the sexual expression of a pro-survival phenomenon.
For example, and the specific case which I have a (unsupported) hunch may be the instance, contemplate male-bonding. This is a social trait to which different individuals have varying degrees of expression. In Paleolithic days, Ogg the Mighty, a classic “loner” figure, might well be able to go on the hunt by himself and reliably bring back the game. But even Ogg is susceptible to a sabre-tooth attacking from behind, or something else equally lethal. And most men are not the mighty hunters that Ogg is.
But if the men are motivated to hunt in a band, they quite literally are watching each other’s back and can use strategies to entrap and catch game. So any genetic influence that selects for a tendency to be willing to team up with other men in hunting is going to be very favorably selected for.
Now, to want to team up with other guys, you have to like them, as friends and companions, huntmates and guys it’s fun to kick back with after a good dinner of roast mammoth haunch. And that comes down to today in male-male friendships, “being a team player,” and all the other variations on the theme.
But under some circumstances, it’s quite plausible that you might see this guy you like and feel close to as someone you might desire sexually as well. And any of a number of possible influences might lead you to that sense of sexual feeling.
The basic gene expression here, of male-bonding, is pro-survival. But as a corollary, it may sometimes express itself as a sexual attraction as well.
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The gene-complex idea is one with some merit as well. Remember that genes do not directly cause physical characteristics or traits; what they do is code for protein formation. It’s in what those proteins cause to occur that they produce the expressions that we term “genes for such-and-such” To require that a particular combination of alleles must express themselves together to produce homosexual orientation would easily account for the low-but-constant percentage of gay people in the population.
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Also consider that it’s possible that a particular gene or gene complex may predispose for homosexuality but require an environmental trigger to cause it to express itself. If 25% of the population has the gay gene, but only about a third of them experience a trigger phenomenon, that would easily account for the proportion of people who are gay. Throw in a sex-linked element, and you could arrive at the twice as many gay men as lesbians statistic often quoted.
Several points here.
#1) In human history, and likely even before in the evolutionary chain when humans had yet to evolve, lesbians would have had no choice in the matter of whether to reproduce. The stronger males would force themselves upon lesbians, and they’d bear children. Thus, while lesbians have long existed, they might have had fun with other women when they could. However, they had no choice to refuse sex with a man, and consequently bear children.
#2) Historically, the primary reason for having children was so that the parents would have someone to take care of them in old age, or if they became ill. Social Security and other social welfare systems are a very recent development. As such, a male homosexual would have had every incentive to take a wife to bear him children. He of course could still have fun sexually with other men as he wished. Think here of gay guys thinking “Yeah, having sex with women is kinda gross, but a man’s gotta do what he needs to to survive in this world.” Note the same logic would apply to lesbians. They might think that sex with men was gross, but if they wanted babies kinda hard to get sperm from their lesbian lover. 
The basic flaws in your logic is the presumption that people always had the free will to choose who they had sex with. And, that they wouldn’t deviate from their sexual preference when it was necessary for their survival.
Variations of this question come up routinely on the SDMB, and here is my routine answer. If a genetic trait for male homosexuality exists (which seems likely), it may be like the genetic trait for hemophilia, which is sex-related. The genetic trait for hemophilia is carried by the female line, but expressed almost entirely in the male offspring. Before the invention of artifical clotting factor, most hemophiliacs did not survive long enough to reproduce. But because their non-hemophiliac sisters were the ones carrying the trait, it continued to be passed on to further generations of male offspring.
Interesting to think about. Genes can have unpredictable behaviors in combination. The simplest example is sickle-cell anemia - if you have one copy, you’re resistant to malaria (hence its commonness among tropical populations). If you have two copies, you have sickle-cell anemia, which is quite problematic.
Clearly in the case of being gay, it’s something way more complex than a single recessive gene. Maybe it’s a side-effect of having several copies of genes that give you particular abilities at home decoration and fashion.
But clearly, whatever the biological component is (and it does appear to be partially biological, at least) it’s a very complex thing. A mixture of several genes, hormonal influences in utero, and to a certain extent childhood experiences. It’s just something complicated enough that it won’t be visible as a single trait and won’t manifest itself predictably. So it’s not as subject to weeding-out as other genes that make reproduction less likely.
Chatting one day w/ a openly, proud homosexual male, he brought up the ‘gay gene’. After the info he provided (I’ll look for the link) it seems more like the gene controls how we feel inside (either m or f). He is a male, but claims to ‘feel female’.
I could accept his statement, but we diverged as to how this effects people.
My take on it was:
m/f gender is seperate from m/f feelings, we have m’s that feel like m’s and m’s that feel like f’s (and the ‘opposite’ holds too).
Society teaches us that gender m’s should have m feelings. But this in not nessesarly true. Reinforced by society, these m gendered f feeling people find themselves unable to really fit in with their like gender and find that they can more easily associate with the opposite gender (since the feeling is the same). This is what could lead to becoming sexually attracted to the same gender (as one sees all the people he associates with on the feeling level (f gender, f feeling) start becomming atracted to the opposite gender.
W/o the current pressure from the society, I would think the gender m, feeling f person would normally find a gender f feeling m person to mate with. And the feeling (m or f) would not be related to gender.
this in my one theory based on what we both read about the gay gene.
His theory was more like, this explanes who I am and it is legit. If that helps him, fine.
(sorry I looked by can’t find the link.)
I’d have thought it would be better to try to establish the facts than to try to develop a convincing argument that might actually be totally wrong.
I think this is generally true of the way in which genes work; it is all too simple for the layman to think that genes have discrete, single functions (I’ve even come across people who thought they were grouped/organised by proximity of function within the genome - that the ‘ear’ genes would be physically closer to the ‘eye’ genes than the ‘toe’ genes).
I’m pretty sure that it isn’t anything like as simple as that in reality and that some genes play important roles in a number of different processes - it isn’t the genome as such that builds the organism, but the web of interactions that occur between the complex chemicals for construction of which the genes are a pattern.
I think this is why some genetic defects have multiple effects (like certain combinations of coat colours being associated with deafness in cats and then only in a specific gender).
Likewise, if there is a genetic basis for homosexuality (and I’m not calling it a defect), it is quite likely to be a complex one and maybe there are multiple, different combinations that result in a similar effect or tendency toward an effect.
Let’s talk about the birds and the bees. Well, just the bees really.
Only a handful of the members of a bee hive are capable of breeding. One queen and the occasional drones. The workers are sterile.
So why haven’t the sterile workers been bred of existence by the Miracle of Evolution? Because this works!
The existence of members of a species who are at a disadvantage (perceived or real) has nothing to do with the expectation that their genes should be flushed out of the gene pool. What works happens, in terms of evolution.
As Triskadecamus points out, such limitations occur all the time in mammals. The naked mole rat, in particular, has a society quite similar to bees.
Having two copies of a certain gene causes sickle cell anemia, which is bad. Having one copy protects somewhat against malaria, which is good. So that gene is found in modest numbers in groups where malaria has been a problem.
Nature works in interesting ways.
About those twin studies, have similar studies been performed for fraternal twins and for siblings of different age? If the correlation for fraternal twins is similar to that for identical twins but significantly higher than for non-twin siblings, then that would tend to support the hypothesis of the prenatal environment being significant, since the prenatal environment for twins should be identical. Of course, even non-twin siblings share the same womb, just not at the same time, so even if there were no genetic component at all, but merely environmental, one would still expect to see some correlation for non-twin siblings. I don’t suppose that surrogate motherhood is common enough yet to be of use in such studies?
Of course, I also presume that any sort of sibling study would use primarily siblings who had been separated at birth, since siblings raised in the same household would have similar environments growing up, and hence the psychological hypothesis would also imply a correlation.
Yes. Fraternal male twins have a lower incidence of dual homosexuality than identical twins, and non-twin male siblings have an even lower incidence of dual homosexuality.
Bailey and Pillard (1991): occurrence of homosexuality among brothers
52% of identical (monozygotic) twins of homosexual men were likewise homosexual
22% of fraternal (dizygotic) twins were likewise homosexual
11% of adoptive brothers of homosexual men were likewise homosexual
J.M. Bailey and R.C. Pillard, “A genetic study of male sexual orientation,” Archives of General Psychiatry, vol. 48:1089-1096, December 1991.