"If infertility and hermaphrodism can have inherited genetic components, surely homosexual behavior, which doesn't affect the plumbing, can have it as well"

And how common are those conditions?

"In a pre-IVF world, all homosexuals had to do was bolster their confidence for hererosex frequently enough to get out a kid or two, and voila, the gene propagates"

Not enough to maintain it in the population at the rates homosexuals are oberseved. Do the math.

And how common are those conditions?

They're uncommon because, so far as we know, they provide no selective advantage.  The wikipedia article even begins with the disclaimer that you have to assume this isn't the case for any genes which promote homosexuality.  I think it's pretty easy to imagine a gene which promotes female fertility and male homosexuality, so at least to me it's premature to write off contributing genetic factors.

Additionally, if you buy the germ theory, how do you explain that homosexuality was present in isolated tribal/island cultures?  They didn't have any of our other diseases, but they somehow had the gay germ?

To stay in the population at levels as high as homosexuality is, the increase in fertility would have to be enormous. If everyone has three kids on average, for example, then the homosexual's siblings would need to have 12 children between them to make up for the him not having kids.

"how do you explain that homosexuality was present in isolated tribal/island cultures?"

It's caused by a common infection. Homosexulity has always been more prevalent in cities, where people are more likely to be exposed to a variety of germs.

If everyone has three kids on average, for example, then the homosexual's siblings would need to have 12 children between them to make up for the him not having kids.

Care to explain your numbers? Even if this gene made all male carriers 100% gay (which isn't how homosexuality is usually found in reality), seeing that human kids are roughly 50% male and 50% female, this would mean that every female of this gene would have to have twice as many children as normal, to make up for the same number of male carriers who have none. In your example, this would be 6, not twelve.

Add to that that it is possible that the gene could have more than one effect, similar to sickle cell anemia, which reduces the life span but increases the resistance to malaria. It is entirely conceivable, it seems to me, that a gene or a number of genes increases the likelyhood of male carriers to be gay (remember that homosexuality is not always a 100% thing. It seems to be a common tendency with higher or lower levels), but delivers some other benefit. For the male carrier this is a bad trade, for the female carrier it is a good trade, in combination it is a slightly bad trade which makes it uncommon, but not extinct.

It is also possible that homosexuality is an inherent trait to how out brains work on sexuality. In nature, not the best way is found and used, but the ways that work good enough. Perhaps when more intelligent life-forms developed their sexual attraction mechanisms that were not only based on chemical stimulants, homosexuality was a by-product and was never fully rooted out. That would explain why it is so widespread in the animal kingdom. Biology has quite some examples of useless by-products that survive long, like when our fetus develops gills-like slits.

In short, the germ hypothesis is based on a very simplified understanding of genetics, it seems to me.

Nieces and nephews have 1/4 of your genes, so to make up for the children you don't have in our example where the average is to have 3 kids, your two siblings would need to have 6 extra kids plus their own 6.

"Add to that that it is possible that the gene could have more than one effect, similar to sickle cell anemia, which reduces the life span but increases the resistance to malaria"

Cochran addresses malaria specifically, and I've discussed it in other comments.

If there is a 'gay' gene, then your nieces or nephews either have it, or they don't.  If you have it, at least one of your parents had it, so your nieces and nephews are more likely than an average person to have the gene as well.  If you are homosexual, and don't have your own offspring, and thus direct your energies towards feeding and rearing your nieces and nephews, that gene is more likely to survive into future generations.  So the theory goes.  It seems at least plausible to me.  The presence of the gene in a particular family creates a higher ratio of productive adults to dependent children than found in the general population, increasing the chances of survival of individual members of the family, and thus the gene.

Imagine two extended families: family 1 with 6 adults (three breeding couples) and 9 children, without the gay gene, and another family with two breeding couples and uncle bob (who is childless and gay), and 6 children.  Some of those 6 children will also have the gay gene, none of 9 children in the first family will have the gay gene.  Absent any resource restrictions, you are correct, the gay gene-less family will out breed uncle-bob's relatives in future generations decreasing the prevalence of the gay gene in future populations.

But what if a famine comes along?  Family 1 has 6 productive adults for 9 dependent children.  Family two has 5 productive adults for 6 children - a clear advantage, whether you are hunting, gathering, or trying to coax crops from drought beset land.  The family without the gay gene is more likely to suffer mortality as a result of any resource restriction.  This mortality could be partial, or total.  One could imagine a situation where uncle bob makes the difference, and all of family 2 survives the drought, while all members of family 1 die.

This is a plausible mechanism by which a hypothetical gay gene could increase it's prevalence in the general population.

"This is a plausible mechanism"

Actually the "Gay uncle" theory is the least plausible explanation.  No one seems to have observed this self sacrificing for the children of others/relatives behaviour in homosexuals. The fitness boost the gay uncle would have to provide and the amount of sacrifice the uncle would have to make don't satisfy Hamilton's equation.

 

What makes you think gay people don't have offspring?  Historically speaking this is simply inaccurate.  There have been quite a few well known homosexual rulers (not to mention Greek philosophers) and almost all of them were married & had children.

Thalia

Rather than an infection, the best explanation I have seen is that homosexuality is an epigenetic phenomenon:  homosexuality is caused by a combination of genes plus some sort of event in early childhood.  You might have the genes, but if you don't have that early childhood experience, you don't become gay.  No, the early childhood experience doesn't have to be sexual.  Personally, I suspect that a certain '70s British sci-fi TV show (which I watched on Nickelodeon) could have made me gay.

It's caused by a common infection. Homosexulity has always been more prevalent in cities, where people are more likely to be exposed to a variety of germs.

Or: Gay people move to places where other gay people live, so that they have a better chance of meeting a soulmate / finding a decent bar / getting laid next Saturday.

To stay in the population at levels as high as homosexuality is, the increase in fertility would have to be enormous. If everyone has three kids on average, for example, then the homosexual's siblings would need to have 12 children between them to make up for the him not having kids.

We already know from twin studies that homosexuality isn't purely genetic.

And anyways, your math is wrong; the homosexual will have more siblings than the average straight male because his mother is hyperfertile.  Especially in times when women have frequently had 10+ kids, something a 20% increase in fertility for a 10% chance that any male son was gay would have been a more than good evolutionary trade.  And that's assuming that the gay sons don't reproduce, which I think is really iffy.  I know several gay guys who have wanted children and been willing to engage in heterosexual sex to get the kids.

And on the germ theory note, if this virus is so omnipresent, how is it that every guy isn't gay?  It would have to be both widespread and extremely contagious if even all the isolated cultures have it; if it's that widespread and contagious, every male in the world should encounter it as an infant and turn gay.  Unless, of course, there was an inherited resistance to it.  But then you're back to some people having the (anti)gay gene.

It would have to be both widespread and extremely contagious if even all the isolated cultures have it

Interestingly enough, the germ also afflicts sheep, penguins, flamingoes, bonobos, ostriches, dolphins, orcas, lions,foxes, bears... oh my! :D

Now with caps!

See my response to Tesjuii comment #18 above.

"why is it that the experiments haven't been conducted to prove or disprove the hypothesis that homosexuality is pathogenic in nature"

1. Homosexuality itself isn't a disease.
   
2. No one has looked very hard for a disease, in part because this is a controversial area of research, in part because of the prevailing orthodoxy (it was only fairly recently that H. pylori was identified as the cause of the stomach ulcers which afflicted 2% of the population), and in part because it can be quite difficult to figure out what it is. The infection occurs at a young age (possibly even in utero), but the effects aren't noticable until adolesence.

"Why is it that we're left to accept Urkel's reference to Cochran's mind experiment "

You don't, but the point is while the pathogen theory hasn't been proved, the genetic theory is demonstrably false. It could be sunsposts or something, or something equally improable. But I doubt it.

It is only demonstrably false if you assume that sexual selection is perfect, or the only determinant of evolution. It is neither. (One link, for the hell of it).

Now with caps!

""They may be maintained by heterozygote advantage"

And the heterozygote advantage of a gay gene is? If it provided protection to a disease we would know what this disease was, because it would have to be a terrible disease that culls populations, similar to the example they give of malaria.  

"They may not really reduce fitness."

We know homosexuality does.

"They may be maintained by mutation."

Such mutations are rare, like the example they give of neurofibromatosis "Natural selection cannot completely eliminate the gene that causes this disease because new mutations arise relatively frequently--in perhaps 1 in 4000 gametes." Homosexuality is 200 times more common than this, so it's not something being maintained by mutation.

"They may be maintained by gene flow."

Homosexuality reduces reproductive fitness everywhere.

"Natural selection may not have had time to remove them yet."

Natural selection has had plenty of time to remove it. A gene reducing reproductive fitness by half would dwindle to less than 1% frequency in fewer than 20 generations.

Homosexuality reduces reproductive fitness everywhere.

Homosexuality doesn't significantly reduce reproductive fitness. The assumption that homosexuals can't and don't reproduce is false. For example, people who marry and have children only to come out as gay later in life are common.

Natural selection has had plenty of time to remove it. A gene reducing reproductive fitness by half would dwindle to less than 1% frequency in fewer than 20 generations.

I've given up any scant hope I ever had of poking a hole in your steely certainty, Steve, but I do have one remark about this, only because it was something I'd been thinking about and just hadn't posted yet. We have a mechanism in our population to keep a gene like that in the pool - society. We have societal norms (and well as complex power relationships, etc) that would minimize the reproductive effect of a "gay gene" on the population. If the argument is that being gay means one is less likely to reproduce, we'd have to prove that's actually true historically. But historically there has been pressure on males to reproduce as part of their role in society - regardless of their sexual preference. There's many examples (all that I can think of are in relatively recent times, however) of men who are free to have sex with men, or who do so covertly, while still filling their role in society by having a wife (or wives) and procreating.

It also brings up another question (though someone else here or at Pl*stic already beat me to it), which is: what do we mean by gay? If by "gay" we mean the religious/conservative (in this country anyway) stance that any sexual contact between people of the same gender is "gay," then really there's less reproductive disincentive to worry about, since, like many other animals that have "gay sex," gay humans would still be reproducing. They would just be getting a little (or alot of) same-sex action on the side. If however, we restrict the definition of "gay" to those who are only attracted to others of the same sex, then, at least in humans, I'd go back to the scenario above.

There is a third option, which is that there's a spectrum of sexual attraction from one side to another. Supposedly recent tests on bi males argues against this, but so far I'm unconvinced. In any case, if there is a spectrum of attraction, then they survival of individuals who are attracted to the same sex but still procreate either out of attraction or some other evolutionary pressure (like society), then some of the that group's children may end up in the more extreme end of the scale - the same-sex only attraction group, which would still survive given a pressure to reproduce (and is it just me, or are women often really hot for gay guys? I mean, really. Sounds like a reproductive advantage to me. Guy dresses well, stays groomed, picks out nice furniture - chicks dig that).

Now with caps!

"If the argument is that being gay means one is less likely to reproduce, we'd have to prove that's actually true historically. But historically there has been pressure on males to reproduce as part of their role in society - regardless of their sexual preference."

For most of human history it's been more difficult for all men to reproduce. In situations of where the number of men exceed the number of women (whether through numbers or polygamy),  where childbirth was hazardous, and childhood diseases common, homosexuals would be out competed because they wouldn't try as hard.

In situations of where the number of men exceed the number of women (whether through numbers or polygamy),  where childbirth was hazardous, and childhood diseases common, homosexuals would be out competed because they wouldn't try as hard.

That's an assumption you're happy to make, but I am not.

Now with caps!

So if homosexuals living somewhere surrounded by lots of other men but few women would make an arduous trek or take a risky sea voyage to where more women were, or spend lots of money to import a woman or go on a raid to capture women. In a polygamous culture they would risk bodily harm to cuckold one of the dominant males many wives.  Sure.

So if homosexuals living somewhere surrounded by lots of other men but few women would make an arduous trek or take a risky sea voyage to where more women were, or spend lots of money to import a woman or go on a raid to capture women. In a polygamous culture they would risk bodily harm to cuckold one of the dominant males many wives.  Sure.

Well, in all of the cultures that your examples spring to mind, it seems there is a strong societal pressure to be seen as a normal, healthy male who can reproduce and be considered successful in life and who can contribute to (and further) the society. If all we had to worry about in life was food and f*cking, then maybe not so much. But we risk bodily harm and risky sea voyages and arduous treks for money, for fame, for power - none of which directly pass on our genes. But were I a gay Viking, or a gay Arab trader or a gay Aztec warrior, or a gay Conquistador or whatever, I think I would find it very advantageous to my health, happiness, and longevity to acquire wealth, power, fame, and in the course of all that a wife (or wives, were I so successful) and  probably even kids (You know, even gay people like having progeny). I'd just have me some dudes on the side. Even today, when the cultural pressure to be gay is arguably far far less than it was in the days when it might get you publicly stoned, thrown in jail, or legally murdered, gay men still marry women and have children.

Now with caps!