Not an expert here but, IF a gay gene existed, wouldn't have it been evolved into extinction?
If such a gene existed (which perhaps it doesn't), it might benefit families who had members carrying it.
This is the same reason some species have evolved alarm-calling when a predator is nearby. It benefits the collective (who share the gene), but at an obvious detriment to the individual's ability to pass on their genes in this case.
(I’m massively oversimplfing of course, my bio knowledge is fairly limited).
(I'm not commenting on whether being gay has a genetic basis or whether it's an example of kin selection, because honestly, I have no idea.)
There is nothing about a possible genetic basis (whether complex and indirect or simple and direct) for an individuals non-reproductiveness that implies it has to result in extiguishing itself.
Humans are social enough that genetics which benefit the group at the expense of the individual are perfectly selectable.
Heck it even works for utterly antisocial species.
All that's required for a trait to persist is for it to be good for any members by any means. It doesn't have to be good for the individual carrier, and it doesn't have to be good in a way that we happen to understand.
> If a gene copy confers a benefit B on another vehicle at cost C to its own vehicle, its costly action is strategically beneficial if p_B > C, where p is the probability that a copy of the gene is present in the vehicle that benefits. Actions with substantial costs therefore require significant values of p. Two kinds of factors ensure high values of p: relatedness (kinship) and recognition (green beards).
The Selfish Gene is probably the most famous way of looking at that concept. https://en.wikipedia.org/wiki/Gene-centered_view_of_evolutio...
For this analogy to be equivalent, it should lead to having gay children benefit the adults enough to allow for more successful breeding.
I do am not commenting on one's gayness has a genetic basis, because I also have not idea.
"If there was a genetic cause for shortsightedness, why is it still around?"
"If there was such a thing as a genetic disease, why haven't they evolved out?"
"If not having X-ray vision was genetic, wouldn't the absence of X-ray vision have been selected out?"
You really can't expect evolution to accomplish its "goals," per se. It is sort of a gentle flow down a lazy river, towards adaptation.
The case with gay genes is different. Regardless of any other trait, I'm genetically prone to not have any offspring. Thus, eventually my genes would be less and less common.
All that's required for a trait to persist is that it benefits the pool.
If the pool benefits from have 1% of members being blind, then so they shall be.
We don't have to understand the benefit for it to exist either.
From Wikipedia, quoting evolutionary biologist Jerry Coyne: "Group selection isn't widely accepted by evolutionists for several reasons."
Or that it's less bad than whatever beneficial trait it's coupled to.
Humans consume a lot of water in order to shed heat. Our backs are pretty f-d up. Our brains waste a lot of energy and require a very long childhood. But on the flip side we're basically terminator compared to the African fauna our primitive ancestors hunted.
It seems reasonable that being gay does significantly reduce your ability to have children; therefore it is reasonable to expect that if it was an inheritable trait it would have been selected against.
We have understood how this is not true for decades or even hundreds of years, and it's not even some impossible concept to grasp.
All that's required for a trait to persist, is for it to benefit the pool, not the individual.
The only way the seemingly obvious but incorrect idea you descibed applies is, a trait which is good for the group at the expense of the individual, if it's 100% effective like sterility unlike say alarm-calling which merely carries a risk for the individual, is that such a trait can never grow to where all members exhibit it.
But it can absolutely be strongly selected for maintaining whatever the optimal percentage is. IE, if it benefits the pool for 10% of members to be sterile, then the percentage of sterile members will not decrease through the mechanism you and so many imagine, but will stay at 10% for as long as the benefit exists.
This is a well debunked belief. Genes are selfish, and they only reproduce to the benefit of the gene.
Group selection does not occur.
An example is evolutionary stable strategies, where cheaters persist in the population, even though the pool would be better off if all individuals in a pool were selfishly altruistic towards pool members.
(1) some people are bisexual and thus would occasionally reproduce and
(2) if sexuality promotes "togetherness" and "group cohesion", then having "our gay uncle who 'has connections' and is always willing to help out the family group" is still beneficial for the family unit and thus a gay gene would not be selected against within that family lineage.
Probably not a majority of the population, but there's no reason for such a "gay gene" (if it were to exist) to be driven to zero.
- 25% both normal alleles (normal phenotype) - 50% one normal allele (normal phenotype) - 25% both gay alleles (gay phenotype)
But homosexuality is not a gene. I believe that the [fetal androgen exposure theory](https://en.wikipedia.org/wiki/Prenatal_hormones_and_sexual_o...) is the one currently preferred.
1. If having gay relatives improved the chances that you will have children and they would survive to themselves reproduce, then evolution could favor maintaining a gay gene.
Remember that for nearly all of our species' existence, and that of the pre-humans we evolved from, we've lived most of our lives in arrangements where our close relatives lived near us and most people in the region were also related to us.
Your children have half your genes. Your siblings' children have a quarter of your genes. So in effect two of your siblings children are equivalent to one of your own as far as getting your genetic material into the next generation goes.
If being gay meant that your sibling does not have their own kids to take care of and so they devote effort that would have gone to raising their own kids to helping their straight siblings' with their kids or to doing things that help the village that those with kids don't have the time for, that might greatly increase the survival rate of those kids enough to make up for not having kids of their own.
2. Being gay doesn't mean you can't have kids. Throughout most of our history, many many people have had kids with people they have not been attracted to. That goes for both gay people and straight people.
3. What if it were a bisexual gene rather than a gay gene? Having people in your tribe that can form with both men and women the kind of close bonds the people form for the sexual partners has some obvious advantages.
* the same gene can have different phenotypes in different individuals. One phenotype may be net negative but the benefit from the other makes it net positive.
* in social animal gene can be carried by relatives. Extreme example is ants and bees, most of them are not fertile but they help to spread their genes by helping those who are.
If it benefits the pool that x% of members have a trait, even full sterility, then the genetics will result in x% having that trait, as long as the benefit continues to exist.
I'm not sure what an example mechanism might be for some mountain cats or spiders or whatever that the species benefits from 4% of their members being sterile, but I see no reason that there couldn't be one, and it doesn't require the unfortunate exhibitors of the trait to preserve and occasionally produce the next exhibitor of the trait.
The naive reaction is: individuals with the "gay gene" won't reproduce and it will eventually die out. A more nuanced perspective is that while that individual won't reproduce, their presence in the community helps the clan's survival, so a community with the gene is overall stronger, so the gene will stay around.
Social pressure to have children, especially if there is a title / wealth / prestige to inherit, would certainly play a role.
Another striking example: Sickle cell disease will only be deadly if both alleles carry the unfortunate mutation. But the unhealthy allele is unlikely to be eliminated by evolutionary pressure because carrying one allele provides significant protection against malaria.
The interactions between genes and their environment is usually more complicated that these simple examples, but I hope it illustrates that evolutionary pressure may not suffice to erase some apparently unsustainable alleles from the population.
That is why sickle-cell anemia mostly shows up in people whose ancestors came from places with a long history of malaria.
There is another hypothesis for why this hypothetical gene might not evolve into extinction. Being gay may just be a side effect of it, with some other benefits being the reason this gene stays in our gene pool.
For example there is a correlation with sibling order and homosexuality. The more boys your mother had before you the more chance you have of being homosexual. We're talking about a non-negligible increase of over 30%: https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male...
[1] Spontaneous = ignoring attempts to "cure" gay orientation.
And evolving out the former would cause the later to go which is detrimental to the overall health of the species.
Not an expert either here though.
I've pointed out on other HN threads that homosexuality has much lower concordance in identical twins (around 40%) than almost any other trait, making it an especially unlikely candidate for direct genetic causes.
Perhaps akin to aging phenomena that benefit the species through mortality.
Doesn't the question apply to straight people, and anyone else, who don't reproduce?
The fact that something is genetic doesn't imply there is no social component. Genetic factors could lead to a predisposition for a certain behavior that would still be altered by environment. There could be many genes that each has some small effect but none of which is an on/off switch. Those would lead to more complicated selection pressures.
We are pretty sure there is a genetic component. We are pretty sure that it isn't just "if you got the gay allele then you's gay".
Also, some gay (or mostly gay) people have children. This is because a) most people are at least a little bit bisexual, b) people may want to have children even if the sex act isn't appealing, and c) there are social pressures to conform.