Good thing then that there has been a follow-up study with a larger and more diverse group that found the same result:
Presumably, they were comparing the families in the sample. Female relatives (most of them Roman catholic) of gay people were more fecund than females (also Roman catholic) who didn’t have a gay relative.
If you study genes related to the production of melanin, it doesn’t matter whether you’re studying Congolese or Norwegians, as long as you don’t compare Congolese with Norwegians.
Depends on the society. This may be true in recent Western societies, but not always in non-Western traditional societies. Some Native American societies were accepting or at least tolerant of homosexuals, sometimes as a “third sex” or as men who lived as women.
According to wikipedia “genetic effects explained .34–.39 of the variance”
Which is quite a substantial proportion, enough to say that it is genetic, although not as highly genetic as say, height.
I addressed this (shortly). Of course there is no hard evidence here, and there never will be. But it seems pretty clear to me that homosexuality will affect the number of offspring. I would expect the homosexual male to tend to have less sex with his wife, to tend to find her later, to tend to not care as much about her looks, and to tend to not be as committed to the relationship as a heterosexual male. And these things affect the number of offspring and the fitness of the offspring.
That depends on the fitness effect of the trait. A fitness effect of ±1% will be fixed in the population rather quickly. An example of this is the recent adult milk drinking mutation.
I agree to some degree. I guess what I am interested in is the most plausible just so story (even though it wouldn’t be backed up by hard evidence), and I don’t think any of the ones I am familiar with are plausible.
Also, I don’t think it’s necessarily like this. Perhaps the right explanation will come along, and it will be obviously correct. Like, assume we didn’t know the evolutionary reason that elephants have big ears. Then I could ask for it, and people could say: “it is not fully genetic”, “selection takes a long time to work”, “perhaps it’s neutral to fitness”, “perhaps it’s to scare away predators”, “perhaps it’s too simplistic Darwinian to expect to make a story about it”, etc etc. But there is a more plausible explanation that I just wouldn’t have thought of, and perhaps that is the case here too.
That’s #2.
I think this is a great point, and I have thought about this as well. There are explanations for these that sound somewhat more plausible (to me) than the explanations for the prevalence of homosexuality. Eg. celibacy for religious reasons could be caused by an even more powerful evolutionary force causing children to believe intensely and unquestioningly in what their parents say. Social shyness could be a result of that the number of people you would meet in your lifetime was much lower in prehistoric times, and therefore the impression that you make on any individual actually is extremely important.
Asexuality is equally puzzling to me though, and I considered including it in the OP. Also abnormal sexual attractions such as pedophilia or zoophilia.
It seems to me that evolution is tripping up over something that should be simple and is hugely important. If I were to design a creature, the first thing I would do is make it desire to survive, and the second thing I would do is make it want to make babies or do things that would cause it to make babies.
Do you have any cite for this, or is it just a WAG?
I find it very strange to assume that female choice would have no evoutionary impact. Why would it be one-sided? It would be extremely interesting if that was the case. It’s not like forcible rape is the most common method of reproduction in humans, or most of the primates (AFAIK).
Birds for example - don’t many species have the male competing via dance, plumage & nest-building with the female selecting her mate based on what she sees? I’m sure there are similar examples in the primate world, if only because the primate world covers vast differences.
So yeah, just wondering if there are actual scientific / evolutionary theories that suggest female mate selection has no impact on reproductive outcome?
Ah, so you did. My bad.
I will disagree with your thoughts on this.
First, there is nothing that says evolution must take the most efficient or sensible route. Very often it doesn’t (e.g. the 15 foot long laryngeal nerve in a giraffe’s neck). There may be some explanation for why a trait for homosexuality is passed the way it is but for all I know it was just chance that it worked out the way it did and it turned out to be an overall beneficial trait for the species.
Second, increased fecundity of females easily outweighs males. It is not a 1:1 relationship. A single male can father many dozens of children. Dropping 2% of males out of the pool seeking female partners doesn’t even make a dent. The other males will happily and easily fill the gap the gay males leave. Females on the other hand have relatively few children so a woman who has six children instead of four or two is not so easily counterbalanced.
Mother Nature would much rather have the females more likely to churn out numerous babies. Whatever males are around will likely be happy to oblige them.
I really like this theory. I’m not convinced though. Couldn’t it work a little harder at getting those last 5ish percent connected right?
One thing I find interesting is the strong finding that the odds of a man being homosexual increases by 33% by each older brother. This tells me that there is something that could be done to reduce the chance of offspring homosexuality by at least 33%.
Actually it looks to me like a system actively trying to create a varied batch. First making some play-it-safe heterosexuals, and then increasing the chances of getting some homosexuals, which will confer some sort of advantage.
You designed a rabbit 
/tongue in cheek
Those first two rules already have some areas of conflict that would need subrules to sort out. Babies take resources which affects survival of current, self sustaining, breeding age adults. Unless you can kick new babies out very quickly after birth and have good survival rates to breeding age, the balance between those two basic rules is touchy.
Too easy for it all to sound like, homosex doesn’t create a fitness advantage, therefore there is something fundamentally wrong with it, or fundamentally wrong with the omniscient evolution that cannot seem to get rid of it. In fact, it is only fundamentalist cultures like the one that dominated Western Europe so long, or the fundamentalists over there who find homosex wrong, and messing around with the wrong sex always persists in the ignorant cultures that find it distasteful. Evolution has nothing to say about sexual preference, some are born gay, some choose to be gay, some just want to jump on anything that comes along on 2 legs. The science of evolution is as challenging and difficult to understand as quantum mechanics, don’t know why people are so quick to think they have some special insight into it, I sure don’t…
And we have virtually no idea how homosexuality was seen in ~99% of our evolution as a species.
Another possibility is that while homosexuality may be congenital, it is not necessarily genetic. Quite some time ago (and I’m sorry I have no cite) I read about a study of pigs. It turns out that a male pig whose position in the womb was between two females was more likely to be homosexual than one whose position was between two males, with similar results for females. So it might be that the womb environment plays a big role. Of course with humans who are not often born as part of a set of triplets, it cannot be as in pigs. Nonetheless the environment in the womb might determine the state of the fetus.
This pushes the problem back one generation. Why don’t women have more welcoming wombs? Well, maybe they have no way of determining sex and it is better for females to get plenty of estrogen and males to get more androgen. But I don’t know; at this point it is all speculation. But suggestive, no?
Actually, birth order of males has been implicated in homosexuality in some cases in humans.
OK, important I’ll grant you. But what on Earth makes you think sexual behaviors are simple?
That’s what I said in post #13, but I didn’t have a cite.
I recalled that someone had mentioned this earlier, but didn’t go back to check what was said.
But it is still the advantage to individuals that cause the anomaly to prevail. In your example it is the individuals who pass on the sickle cell gene because it benefits them (or at least doesn’t kill them before they can reproduce). The “gay uncle” hypothesis doesn’t work the same way because any genetic anomaly, even if helpful to society, would die with him and not be passed on to the next generation.
I vote for the in utereo suggestions stated upthread. That makes the most sense.
Right. I remember reading years ago that women with male fetuses who experienced severe stress at a very specific stage in pregnancy were more likely to bear boys that went on to be gay. An example was women who were in London during the Blitz. Googling this just now, I found a cite, but I can certainly understand how this could be a radioactive area of scientific inquiry (similar to race and IQ): on the one hand, it disproves the notion that homosexuality is a “lifestyle choice”, but it also comes awfully close to sounding like a birth defect.
I also like the “gay uncle” hypothesis, at least as a corollary that helps explain why a gene would not develop that would actively cancel out these congenital effects. There are many evolutionary survival strategies (ESS) that achieve relatively equal success despite radically different “methods”, and thus fall into a semi-stable stasis or cycle in a somewhat predictable way. For the most obvious instance: quantity over quality can work: go spread your seed as far and wide as you can. But not all men do this, and though women’s mate selection is a big part of it, it’s also because sticking around and really concentrating resources on a smaller number of offspring can pass on your genes as well as just leaving them for the mother to worry about.
Recognize members of the opposite sex, and desire to do sex with them. Seems way less complex than say, language capability, or the liver.