General Question

blaze626's avatar

Assuming there exists a necessary genetic component to homosexuality, will the population go to zero someday?

Asked by blaze626 (151 points ) July 7th, 2011

Note that I do not wish this on the population in any way, I’m asking purely as an academic curiosity. I’ve read related threads, but am unsatisfied with the answers I’ve found.

The gay population is inherently less evolutionarily fit than their heterosexual counterparts, so it seems the population would disappear someday. It makes sense that it hasn’t happened yet due to cultural pressures to reproduce in the past (in order to maintain a straight façade), supporting a synthetic fitness that has allowed the gay population to increase with the majority population. But now that cultural pressure is mostly gone, it will be less likely for a gay couple to have biological offspring than a straight couple, thus driving the gay population to zero.

I imagine we don’t see the gay animal population driven to zero because they continue to have reproductive sex in addition to gay sex (Possibly at an even higher rate, considering hormonal implications).

Of course, if it turns out there is not a genetic precondition necessary to be truly gay, my entire question is moot. And of course I acknowledge there will always be people who have gay sex just for fun. My question refers to the population of genetically gay humans only.

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53 Answers

Simone_De_Beauvoir's avatar

“The gay population is inherently less evolutionarily fit than their heterosexual counterparts, so it seems the population would disappear someday”

- actually, from what I’ve read of evolutionary theory around homosexuality, it is not in competition with heterosexuality but is a complement to it for the survival of all involved.

“It makes sense that it hasn’t happened yet due to cultural pressures to reproduce in the past (in order to maintain a straight façade)”

Gay people are no less likely to want kids than straight people. Now, with the stigma slowly decreasing, there will be options open to them that have not before in terms of repro technology and in fact more queer will reproduce, muahhahhah (example: me..though of course I did it the old fashioned way, by sticking a penis into my vagina). Also, even though there is some evidence to homosexuality being genetic, it doesn’t mean that straight people don’t give birth to queer people ‘cause they do all the time.

Also, what’s the difference between ‘genetically gay humans’ and ‘humans who have gay sex for fun’? LOL

Response moderated (Unhelpful)
marinelife's avatar

No.

You are making the assumption that the genetic component is only passed down by homosexuals who reproduce. That is not the case.

The percentage of gays in the population is relatively stable.

blaze626's avatar

Think about it a little deeper, whitenoise, then follow the rules for general discussions and offer something helpful.

Simone, I agree that gay couples are just as eager to have kids as straight people. It would just be more difficult to have biological offspring as someone would have to go outside the relationship or take advantage of technology to produce them. This is cumbersome relative to straight couples who can easily (unfortunately) have kids whenever they want.

Thanks marinelife, that’s what I meant though, the number of gays is increasing with the population (i.e., % staying stable).

Also, you guys are referring to a recessive trait, which would also disappear in the population if it contributed to lower fitness. It acts pretty much the same, it would just take longer to expire from the population. I’m not saying this would happen overnight, I’m talking about evolutionary time here…

Simone_De_Beauvoir's avatar

@blaze626 Right, but queer people have always existed and not because they were pressured to reproduce and the times we live in now aren’t going to lead the ‘recessive trait’ (evidence, please) to disappear. I’m not sure if you’re worried or jubilant about that, exactly.

marinelife's avatar

@blaze626 You are making assumptions that homosexuality implies less fitness or serves no purpose. You don’t know that.

blaze626's avatar

Oh and if it is so that there is a genetic component for homosexuality, there will always be people without the genetic component who have gay sex anyway. That is the difference between genetically gay humans’ and ‘humans who have gay sex for fun, as I’ve put it.

Simone_De_Beauvoir's avatar

@blaze626 How can you know they don’t have the genetic component and if they don’t, why would they have it ‘just for fun’? Do you think the rest of us who are ‘genetically queer’ do it out of punishment for our sins?

bob_'s avatar

There have always been homosexuals, and yet the world population has increased significantly. I’d say we’re fine.

blaze626's avatar

Simone, I’m calling “gay gene not necessarily passed from gay parents” the recessive trait. Rest assured I have nothing against or for gays or any other group of people.

Marinelife, great point! That’s exactly what I’m fishing for, some possibilities as to why that may be.

syz's avatar

I don’t understand the premise of your question. Are you indicating that gays are only produced from gay parents? That’s a patently erroneous assumption. Homosexuality is not a directly inherited (recessive) trait.

tedd's avatar

Ok I think you are all missing the point of his question, and jumping to the conclusion of calling him some kind of bigot. The OP’s question was whether or not evolution would trend homosexuality to non-existence because homosexuals could not pass on the “gene” that causes homosexuality. The question is based on assuming homosexuality is caused by genetics entirely (which is another debate in and of itself).

Speaking in terms of Evolution, if homosexuality is a genetic trait…. then yes presumably following the rules of evolution it would some day trend to zero, since those who would possess the “homosexual gene” cannot reproduce amongst themselves (strictly speaking). They can adopt, they can raise children, and they could even sire children from a separate heterosexual relationship, but in the purely homosexual relationship they cannot pass on those genes that cause homosexuality.

The genes would be passed on in the genes of their relatives, much like the genes for an albino squirrel or Tiger or something are passed on in their non-albino relatives, but someday evolution would trend them to zero because in terms of EVOLUTION they are not genetically fit.

Prosb's avatar

@tedd Already beat me to the point I was about to make as I read the question/answers. This is an entirely hypothetical question people, no reason to become so riled and miss the mark entirely . . .

blaze626's avatar

Thanks Tedd, it’s hard to get a thoughtful response to an honest scientific question in an open online forum. Thanks for reading my question thoroughly and giving a great answer.
Those were my thoughts exactly, I’m just looking for another perspective I may have missed.

Mamradpivo's avatar

While sexual orientation has a genetic basis, it is far too simplistic to assume that there is a “gay gene,” the way that there is a “gene” for green eyes. Sexual preference consists of the interplay of thousands of individual developmental and physiological preferences from dopamine receptors to sense of smell… It is not a hereditary trait in the sense of Mendelian genetics.

blaze626's avatar

But doesn’t natural selection still act the same? If there is a necessary genetic precursor, even if homosexuality is 99.9% environmental, won’t the pop still go to zero?

I suppose maybe not if the combination of genetics that produce a homosexual may be pushed by environmental factors to produce a trait that is more advantageous instead of or in addition to homosexuality.

wundayatta's avatar

One theory I’ve heard is that homosexuality provides extra hands to care for the kids. Homosexuals would be more like to be teachers, or they would help their siblings or other people in the community with their kids. This can be especially helpful with overwhelmed parents. So, this theory speculates, the evolutionary advantage is in having greater survivability of children related to the homosexual person.

tedd's avatar

@Mamradpivo You’re missing the pretext of the question. We know that there is clearly a larger debate/question as to the “cause” of homosexuality. For the sake of this question the OP is assuming it is genetic, purely genetic.

SavoirFaire's avatar

@blaze626 Even if there were a necessary genetic precursor, the population would not necessarily go to zero. Since you are assuming it is recessive, there would be many carriers. These carriers would not themselves be homosexual; but if homosexuality presented any sort of advantage in the way that @wundayatta mentions, those who were carriers would be more likely to survive. Thus the number of carriers would increase, leading to the continued existence of actual homosexuals (when two carriers both passed on the recessive gene). The process would then repeat, thus perpetuating the existence of the gene and its manifestation.

@tedd Actually, I think you are missing @Mamradpivo‘s point. Even if we assume that homosexuality is purely genetic, that does not mean there is a gay gene. Genetics is a far more complicated business than that. I have used the “gay gene” model in my response to @blaze626 for the purpose of simplicity, but the actual mechanism would likely be far more complex even under the assumption that homosexuality is purely genetic (or has a necessary genetic precursor).

tedd's avatar

@SavoirFaire If there is a “gay gene” and it is purely genetic, then by the simple definition of how evolution works, the population would someday go to zero. Survival of the fittest is defined by those who are able to pass on their genes to their offspring, it is not determined by those who are simply the most fit physically or what not. The gene being recessive or dominant would have nothing to do with it…. in the end it would come back to the fact that in a purely homosexual relationship someone couldn’t pass their genes on.

In fact if it was recessive and carried on by the heterosexual members of our species, it would eventually fade out as recessive genes do over time. That’s why there are no Neanderthals or Cro-Magnon’s walking around today born to homosapien parents.. despite the fact that we still carry their genetic traits.

IF we are assuming homosexuality to be genetic, then like it or not it comes down to a simple fact, no matter how fit a homosexual may be for surviving themselves, they cannot pass their genes on, and eventually the recessive genes passed on by their heterosexual cousins would disappear due to evolution.

Simone_De_Beauvoir's avatar

@tedd But, again, queer people have always and will continue to pass on their genes whether it was because they forced to ‘live straight’ or because they will now be able to lead normal lives with children.

MissAnthrope's avatar

Simple point: Most gays come from straight, breeding parents.

tedd's avatar

@MissAnthrope @Simone_De_Beauvoir You’re both missing the pretext. I don’t for one second believe that homosexuality is some purely genetic trait. I think its probably caused by a list of reasons working in combination, including genetics sure, but also environment, family, conditioning, etc, etc, etc.

My point that I am trying to make under the pretext of this question, is that IF it was purely genetic and evolutionary, then it would be doomed to extinction under the very most basic of evolutionary laws.

Simone_De_Beauvoir's avatar

@tedd No, for the time being, I am buying into this pretext and I’m saying that gay people do reproduce and will reproduce. If, for some reason, gay people wouldn’t get pregnancies going and only had same-sex their entire lives…even then we don’t know for sure that the gay gene would disappear or how long it would take.

tedd's avatar

@Simone_De_Beauvoir Well assuming they had heterosexual relationships that produced offspring, then yes they would continue on. But even then, if you had a heterosexual relationship with someone who is presumably heterosexual and it produced offspring, the odds of that offspring having your gene (be it dominant or recessive) is only 50%. And if its recessive the odds of them passing it on to their offspring should they mate with a purely heterosexual partner is a mere 25%. The gene would be inevitably doomed.

And we do have a rough idea of how long it would take for the gene to disappear, though nowhere near exact. Homo-sapiens (modern humans) mated with and coexisted with cro-magnon and neanderthal humans. But neither of those species of man was fit to continue on, homo-sapiens were better suited and hence even though there was interbreeding, homo-sapien genes dominated out. Hence there are no neanderthals today (though you and i both carry their genes).

If it makes you feel any better about it, the same goes for humans. Evolutionary history suggests mankind as it exists today (homo-sapiens) will probably be extinct within 100,000 years or so.

SavoirFaire's avatar

@tedd You are missing the point. Recessive genes continue to exist in people who do not manifest them. Therefore, heterosexual people could carry the homosexual gene. Therefore, two people who were both carriers could both pass on the gene and create new homosexuals. This much, I take it, you do not disagree with. Where you disagree is unclear, however, as you say contradictory things in your response.

First you say it doesn’t matter whether the gene is recessive or not, then you go on to say that recessive genes fade over time. The latter claim is patently false. Having five fingers is recessive, for instance, but it has obviously dominated the scene. The bit about Neanderthals and Cro-Magnon is also strange. Leaving aside the fact that Neanderthals are not our ancestors, the differences are determined by overall genotypes. There is no “Neanderthal gene” or “Cro-Magnon gene.” As such, the comparison is irrelevant under the assumption that we are discussing something for which there is a gene.

As to the definition of evolution, I do not think you have it right. Yes, the survival of fit individuals is not the mechanism of evolution. You’ll note that I said nothing contrary to that. What I said was that if something like @wundayatta‘s theory is correct, then homosexuals would contribute to the survival of the “gay gene” not by passing it on themselves, but rather by making it more likely that heterosexual carriers of the gene would pass it on. Those without such support—again, under the assumption that @wundayatta‘s theory is correct—would not do as well. Carriers would become more plentiful than non-carriers under this theory, thus the “gay gene” could continue and thrive even if no one who is genetically homosexual passes it on directly.

It is false, however, that homosexuals cannot pass on their genes. I had a professor who was three children into a marriage before realizing he was gay. Being homosexual does not entail having only homosexual sex, just as being heterosexual does not entail having only heterosexual sex. As such, the hypothetical “gay gene” could be passed on directly from time to time, further increasing the likelihood of it continuing into the future.

tedd's avatar

@SavoirFaire Recessive genes fade over time, you will notice that most geneticists think humans will not have 5 fingers within several hundred years, but 6… because as you stated 5 fingers is a recessive gene.

Humans living today carry genes from cro-magnon and neanderthals, not because we evolved directly but because we existed and inter-bred whilst sharing the planet. Every human on the face of the Earth today has genes from neanderthals, they are simply recessive and buried away in their genome, and not expressed.

So in some sense yes following strict evolutionary rules homosexuality as a gene would live on, but eventually it would no longer be expressed. It may take thousands upon thousands of years, but it would eventually trend to zero.

Evolutionary and genetic laws come back to one thing and one thing only, you have to pass your genes on. Ensuring the survival and reproduction of a relative of yours who carries a recessive homosexual gene will not ensure that the gene continues to exist long term. Even passing the gene on through a forced heterosexual encounter means you have to have a heterosexual partner to mate with, who is just as likely to pass their “straight gene” onto the offspring.

I feel you guys are taking this as some kind of assault on homosexuality or homosexuals when it is not. It is simply evolutionary fact. If you can’t pass your genes on, you will lose in the long run of evolution. Hell even if you can pass your genes on, some day you will lose.

SavoirFaire's avatar

@tedd Having six fingers is maladaptive, which is why the trait went away in the first place. I have never met a geneticist who thinks we will evolve into having six fingers in the near future (and several hundred years is incredibly quick for this change to occur given that the last change in our hand structure was the elimination of the trait you say will be making a comeback). I will need evidence that this is a consensus position and not something you’re just throwing out there to save face.

Second, I didn’t say that we had no Neanderthal genes. I said they are not our ancestors, which contributes to the irrelevancy of your comparison. The main point, however, was that having genes from Neanderthals is not the same as being a carrier for something that is not expressed. There is no “Neanderthal gene” that simply fails to be expressed in me. I could not become a Neanderthal by giving full expression to the Neanderthals’ contributions to my genetic code. That is not what being a Neanderthal (or Cro-Magnon) involves. Thus the comparison makes no sense.

The situation is different if we assume the existence of a “gay gene.” Because unlike being a Neanderthal or Cro-Magnon, which requires a whole host of conditions to apply, one would either have or not have two copies of the “gay gene” under the theory we are being asked to consider. Thus the gene would be likely to keep finding expression if something like @wundayatta‘s theory is correct (the other hypothetical that frames my reply). It perpetuates itself indirectly under this scenario, and the nature of the gene—which is much different than the nature of being a Neanderthal or Cro-Magnon—means that its expression is also perpetuated indirectly.

Note that I said nothing about ensuring the gene continues. Nothing can ensure genetic survival. What I said is that it would keep the gene around, increase the likelihood of two copies finding their way into a person’s genotype, and thus increase the likelihood that homosexuality would continue to be expressed. Thus my response was that “even if there were a necessary genetic precursor, the population would not necessarily go to zero” (emphasis added). There is a clear path to homosexuality surviving even if it were purely genetic or had a necessary genetic precursor.

Finally, I have not made any comment along the lines of “this thread is bigoted” or “you guys are attacking homosexuality.” Like you, I have taken the premise quite seriously despite whatever I may think about its truth. You are trying to group me in with other responses because it is convenient, not because it is accurate. I simply disagree that the premise leads to the conclusion that homosexuality would die out were it genetic. I find your understanding of evolution and the putative evolutionary facts to be simplistic, and so I am expressing my disagreement.

By the way, your last sentence is a rather odd paper tiger move to make. It should go without saying that all genes will go away eventually insofar as all life as we know it will eventually end. If the question is to be coherent at all—and I think it is—it must be about whether or not homosexuality being genetic would cause it to go extinct at a rate notably different than any other gene.

tedd's avatar

@SavoirFaire ok the entire genome of neanderthal or cro-magnon may be too much.

But lets take for example the fact that human beings currently have single genes of individual traits from ancestors extinct for millions, if not billions of years, in our genome, that are not expressed. The fraction of your DNA that actually makes you look like and act like a human is TINY in comparison to your entire DNA, which is full of “garbage” DNA from prehistoric ancestors that disappeared from the face of the planet millions of years ago but is maintained by our imperfect evolutionary system. For example, homo-sapiens share somewhere in the ball park of 99% of the exact same DNA code with chimps (our closest living relative). The majority of that 99% is DNA from our common ancestors, which is no longer expressed, and probably hasn’t been for millions of years.

Homosexuality, if it were a gene, would go the way of these genes. It has no direct way of passing itself on, and sooner or later it would fade into the genome and no longer be expressed, and homosexual members of the species would trend to zero. It cannot indirectly perpetuate itself in the long run, because you cannot perpetuate a gene that is recessive for the long haul. A few hundred generations, thousands maybe even millions of years, sure…. but sooner or later the gene would fade and the species with that trait would trend to zero.

I don’t mean to insult your intelligence or education by any means, but have you ever taken a genetics class?

tedd's avatar

@SavoirFaire Another good example would be the appendix. Within the last 20 or 30 thousand years the appendix has gone from a basic “second stomach” that humans used to digest raw meat, into a basically useless vestigial organ. It no longer serves a purpose, and the genes that actual “activate” it and make it do its job are no longer expressed, because the stomach we do use took over and was perpetuated instead. Eventually the appendix will cease to exist all-together, and in fact today there are some rare cases of children born without them entirely.

Nimis's avatar

From my personal (and admittedly limited) understanding, I’d say no.

Since I’m in the nature (versus nurture) camp when it comes to homosexuality, it would make sense that it is carried on a recessive gene or a particular grouping of genes or alleles. (Being that two heterosexual parents can have a homosexual child.)

Even with more reproductive options, I’d agree that homosexuals have a lower fitness because these options usually require more resources than traditional reproduction. Less educated or less well-to-do are less likely to reproduce. Though you could argue that this increases their overall fitness by natural selection.

I also read a study somewhere (trying to find it), that said larger families had a higher rate of homosexuality. In which case, I’d say homosexuals have a higher inclusive fitness. Less (direct) offspring + more resources = increased inclusive fitness.

If anything, with our decreasing world resources, breeders might “breed”
themselves into extinction. Ha.

squirbel's avatar

Reading this was frustrating because it was like a discussion between someone who understands science and someone who understands politics.

Please, take the politics elsewhere and let this be a scientific discussion.

blaze626's avatar

I wish I could understand both.

crisw's avatar

@tedd

“My point that I am trying to make under the pretext of this question, is that IF it was purely genetic and evolutionary, then it would be doomed to extinction under the very most basic of evolutionary laws.”

Nope- wrong, sorry.

There are a great many reasons why the genes could persist.

One current theory (an this has been brought up many time in other conversations here, it’s not new news) is that females who carry the “gay genes” are far more fertile than their counterparts who do not. So, even if the gene reduces reproduction in males who get a double dose, it boosts reproduction in females enough to keep it strongly selected for.

Brian1946's avatar

@crisw

“One current theory (an this has been brought up many time in other conversations here, it’s not new news) is that females who carry the “gay genes” are far more fertile than their counterparts who do not.”

From my subjective perspective, that’s good old news if it turns out to be true.

tedd's avatar

@crisw So what would females carrying the gay gene being more fertile, have to do with passing on the gay gene? The gay gene would have no effect on fertility, it would be completely separate.

Is is becoming increasingly clear to me you don’t understand genetics.

dannyc's avatar

I hope not. Gay people are important, successful members of a diverse society and actually improve the genetic pool. Any group that has fought so hard for their rights has perfect genes to me and we would be wise to cultivate and pass them on by all means possible.

crisw's avatar

“So what would females carrying the gay gene being more fertile, have to do with passing on the gay gene? The gay gene would have no effect on fertility, it would be completely separate.”

Did you read my link?

Here is the possible explanation, in plain English. Gender in humans is determined by two chromosomes, X and Y. if you inherit an X from each parent, you are female. If you inherit an X from Mom and a Y from Dad, you are male.

Many genetic conditions in humans are X-linked- that means that the genes for them are found on the X chromosome. That means that, if a male inherits a copy of the gene, it’s always expressed- because he has only one X chromosome.

So, if a gene that boosts fertility n females but can lead to gayness in males is on the X chromosome, those women who have it, and have more children, pass on copies of the X chromosome with that gene. And, if they have a son, their son may have the gene. Specifically, if they have the gene on one of their X chromosomes, 50% of their sons will have it; if they have it on two, 100% will have it.

“Is is becoming increasingly clear to me you don’t understand genetics.”

I am not sure why the ad hominem attack is necessary.

tedd's avatar

@crisw The point in the “ad hominem attack” was to point out that simply because a gene is passed on en-masse, doesn’t mean it is expressed perpetually. I still carry all the genes to make my appendix digest raw meat, yet none of them are expressed. Women carrying and passing on the gay gene via their extra X chromosome, just as they pass on baldness in men, would not have any effect on whether or not that gene would be expressed/recessive/dominant. The gay gene would be different from whatever gene made the women more fertile, they would be two genes not one (that’s not how genetics work). And since the “gay gene” would be superfluous and un-expressed in the people passing it on (IE the people with the expressed “straight” gene), inevitably the gay gene would fall into un-expression, or out of the gene pool all together.

That is basic genetics, and your failure to comprehend it is the reason I ended my last post with the ad-hominem “attack.” (which honestly was more of just a publicly stated realization)

blaze626's avatar

Thank you tedd, this is a great explanation of the premise of my question.

I think most of these comments are correct and coming from reasonable perspectives, but I was asking from evolutionary theory that gene expression will go to zero or 100% ultimately.

laureth's avatar

Tedd, perhaps the “gay” X chromosome expresses differently in males (gay) as in females (extra fertile). It doesn’t just translate into gay females, it translates into fertile (likely straight) females.

Why would it recede? Perhaps you’re thinking is because we don’t need homosexuality, just like we don’t need to digest a bunch of raw meat. But if by receding it would take away that extra fertility boost, there’s no incentive for it to recede, so to speak. In fact, by promoting fertility, it’s likelier to make more of itself.

crisw's avatar

@tedd

“The gay gene would be different from whatever gene made the women more fertile, they would be two genes not one (that’s not how genetics work)”

No, they are not two different genes. They are the same gene.

The current working hypothesis for the female fertility booster gene is that it works by increasing attraction to men. Obviously, if you are female, this is great for reproductive purposes, but it isn’t so great for men.

So why is the gene expressed in males?

As I mentioned- number 1, it’s on the X chromosome. So, as males have only one X, there is no corresponding “normal” gene on another X chromosome to balance it. If your theory that non-utile genes should always disappear were correct, then X-linked disorders- many of which, unlike homosexuality, are medically dangerous- should not exist. But, in reality, there are dozens of X-linked disorders that endure in the population- hemophilia, muscular dystrophy, color-blindness and so on.

Number 2— as was mentioned, the gene is assumed to confer strong advantages to females. Therefore, any regulatory genes that shut down this fertility boost would actually be selected against, as the females who carried them would be less fertile. In addition, most of the regulatory genes for male development reside on the Y chromosome. Therefore, in order for the gene to be suppressed in males but not in females, you’d have to evolve a complex, multigenetic regulatory system based on a Y-chromosomal regulation of an X-chromosomal gene. And, as far as evolution is concerned, there simply isn’t enough selection pressure for this to happen. Things don’t evolve because we think they should. Evolution has no direction.

Perhaps you can explain, in scientific terms, why you feel that the gene should not be expressed in males?

tedd's avatar

@crisw If the gene is on the female’s second X chromosome, then a male couldn’t carry it, because they don’t have that X chromosome, they have a Y chromosome which would simply not carry any genes that were extended on the X. Again, basic genetics, which you are not getting here.

And also you are now assuming multiple gay genes. This debate has been, or at least I’d assumed, involving one gay gene that would make homosexual males and females, and not simply be a gene that would spark physical attraction to males. Furthermore physical attraction to males would not increase fertility, it would simply increase the likelihood of mating.

tedd's avatar

@laureth It would recede because it isn’t being expressed, it would have nothing to do with its value to us. Being able to digest raw meat would actually be very helpful to humans, it would save us a lot of medical issues. But the genes simply are not expressed, and have drifted into the DNA abyss.

laureth's avatar

Um. A female passes either of her X chromosomes to her son. It doesn’t have to be her “first.”

tedd's avatar

@laureth….............................................................................................................................................................. Did you seriously just say that?

Well I’m going to give you a brief explanation. No, in fact the mother would not give her child one of her final X chromosomes at random. The X chromosomes all carry very specific genes, and are not interchangeable at all. If a single gene is missing from even one specific X chromosome, it can end in some kind of mutation, let alone if you completely switched them around.

Please, please, please, please read up on this before commenting on it.

laureth's avatar

Tedd, the mother can pass either X chromosome to her children. She doesn’t just make one copy, she copies both: just as the father can pass either his X or his Y on down.

A little more than halfway down the page, this site has a chart that explains it nicely. :)

tedd's avatar

@laureth Just facepalm.

I have nothing else to say in this thread. It’s clear to me that you people are standing up for homosexuality in this case because you view this as some kind of assault on it, even though I outrightly stated from the get go that I do not believe that homosexuality is caused by some singular gene. Your understanding of genetics is inferior to even my amateur knowledge of it, and debating it with you guys is like trying to explain calculus to an elementary student (no offense, but seriously).

I will leave it with one outright comment that I feel I have strongly explained over the last few days. IF (notice the if) homosexuality were caused by some specific gene (and I mean homosexuality in men and women, by one gene), then carriers of that gene would not be able to pass along their genes since they could not product biological children in a homosexual relationship. Eventually, over the course of thousands, if not millions of years, the homosexual gene would trend towards zero, as the gene would be either unexpressed, or simply disappear all together. A population of heterosexual’s passing along the gene secondarily would not sustain a permanent homosexual population any more than a population of neanderthal gene carrying humans was able to sustain a population of neanderthals.

Take your politics out of it, its simple science, and frankly the mere existence and persistence of homosexuality in species acrossed the planet for thousands if not millions of years would seem to dictate that there is a lot more to it than one gene.

laureth's avatar

For what it’s worth, my mom is a lesbian. Even though two women cannot produce a biological child together, lesbians can, and do, breed.

tedd's avatar

@laureth Even reproducing heterosexually with heterosexual mates would only prolong the inevitable. If it was some kind of gene that would go either expressed or unexpressed, the odds of it being passed onto the offspring of some heterosexual copulation would already be halved at best, and the odds of the child passing it on even smaller, and so on and so forth through the generations. This isn’t to say I don’t think homosexuals can have kids, or would be bad parents or something, this is simple science and genetics.

laureth's avatar

Please keep in mind that you are making several unwarranted assumptions here (chief among them, that the same gene would affect males and females the same way, and that there is just one gene that does the whole gay-making job), and then saying how those qualities would make a genetic basis for homosexuality unlikely. Great, so it would. But the fact that homosexuality soldiers on despite your assertions tells me that the assumptions you’re making are not necessarily on par with reality.

crisw's avatar

@tedd

“If the gene is on the female’s second X chromosome, then a male couldn’t carry it, because they don’t have that X chromosome, they have a Y chromosome which would simply not carry any genes that were extended on the X”

Nope. Which X chromosome is in the egg is a matter of chance. It can be either one of the mother’s X chromosomes. Again, think of the X-linked recessive disorders I mentioned earlier. If the mother carries the gene for “Duchenne muscular dystrophy”, let us say, 50% of her sons will have the disorder, because 50% will inherit the X chromosome with the faulty gene. The other 50% will inherit a normal gene from the other X chromosome and will not be affected. Similarly, 50% of her daughters will be carriers of the disorder, and 50% will not.

“And also you are now assuming multiple gay genes. This debate has been, or at least I’d assumed, involving one gay gene that would make homosexual males and females, and not simply be a gene that would spark physical attraction to males.”

Don’t know where you got that. It is very obvious that sexual orientation is not controlled by simple Mendelian inheritance alone.Genetics are a factor, but I know of absolutely no reputable scientists who claim that there is one single “gay gene.”

“It would recede because it isn’t being expressed, it would have nothing to do with its value to us. Being able to digest raw meat would actually be very helpful to humans, it would save us a lot of medical issues. But the genes simply are not expressed, and have drifted into the DNA abyss.”

Again, this doesn’t make sense. If a genetic mutation occurred that allowed humans to take advantage of a new food source, and that mutation thus gave some individuals a reproductive advantage, that mutation would become more common. There’s actually a good instance of this in humans-the ability to digest milk after infancy. This mutation is so beneficial, in fact, that it evolved at least twice.

Also, I see a confusion in your writing about the meaning of “expressed.” In genetic terms, an “expressed” gene is any gene that produces a functional gene product. A gene that is not expressed is one that you possess, but that does not produce a functional product, due to mutation, action of regulatory genes that block expression, etc.

“No, in fact the mother would not give her child one of her final X chromosomes at random. The X chromosomes all carry very specific genes, and are not interchangeable at all..”

As mentioned above, which X chromosome goes into an egg cell is random.

“If a single gene is missing from even one specific X chromosome, it can end in some kind of mutation, let alone if you completely switched them around”

Sorry, but this does not make sense. A missing gene is completely different from a mutated gene. And ” let alone if you completely switched them around” doesn’t make any sense in this context. Switched what around?

crisw's avatar

Oh, and another thing.

Let’s assume (even though it’s incorrect) that there is a “gay gene” carried on the X chromosome, and that 100% of males who have it will be gay. Will this gene thus be eliminated from the population?

No. As I mentioned earlier, there are quite a few- X-linked recessive traits that are actually harmful. Males who have these traits die before they are old enough to reproduce or are so handicapped that they are unable to reproduce. Yet these genes still persist. Just a few of them:

Duchenne muscular dystrophy carried by , affects 1 in 3600 males.
Opitz-Kaveggia syndrome
MASA syndrome
Nasodigitoacoustic syndrome affects about 1 in 2000 European males
Lowe Syndrome
Renpenning’s syndrome
Smith–Fineman–Myers syndrome
X-linked spinal muscular atrophy 2

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