For most of history whatever your sexuality, you married and had children. Period. You also did whatever else you did, and maybe you had a terrible marriage, but that probably wasn't unusual for straight people for most of history either.
Actually no, historically large percentages of the population (whatever their sexuality), especially the male population, did not marry as it was very expensive to start their own household. That's one reason why so many gifts were traditionally given for weddings. Though you do have a point WRT divorce being very uncommon.
Let me expand my objection, homosexuality not only exists in humans but in many other animals, many of which do not have social stigma of homosexuality.
He's not saying that they shouldn't exist today, just that their genes will never make it back into the collective gene pool, stopping their traits and characteristics from ever propagating forward.
But that's not how how genotypes and phenotypes work for recessive alleles. Homosexual genes will continue to live on and propagate in heterosexuals so long as they aren't eliminated by the gene therapy as seen in sci-fi horror/suspense Hollywood films.
It doesn't require a homosexual parent to have a homosexual kid.
'But that's not how how genotypes and phenotypes work for recessive alleles.'
Recessive alleles aren't immune to natural selection. It's just harder to purge them because they get exposed as phenotypes less often. As they become rarer and rarer (it'll manifest as a phenotype as the square of its frequency), selection weakens. Homosexuality, however, is common enough and the fitness penalty large enough that any recessives are exposed to a lot of selection, so it should be disappearing fast, but it isn't, which raises a lot of questions of what exactly causes homosexuality.
Exactly at the heart of the problem. IANAB (I am a physicist though) and from what I understand, it is a question currently being researched. I mean, great example is if it is so easy, why is there homosexuality in the animal kingdom where they don't have social push for heterosexual mating?
Yes, there is extensive research on this subject in ethology.
One hypothesis that seems to be fairly strong is that homosexuality is, essentially, just one manifestation of the broad altruism strategy.
Think about what makes altruism in general persist, despite it been seemingly harmful for its carriers long-term: they might not maximize the likelihood of survival of their own progeny, but in sacrificing that, they increase the likelihood of survival of progeny of people from the same family, tribe or larger community - which have a certain amount of shared genes. If you think of the natural selection game as fundamentally centered on the genes rather than their carriers ("selfish gene" etc), this strategy makes perfect sense - your altruism may result in a lot more people surviving and carrying genes shared with you, and down the line, the end result is that population in the future will be genetically more common with you than it has been otherwise - so your genes "win". If so, the tradeoff is in favor of altruism over selfishness, and altruism becomes a selected trait.
Now, homosexuality can be seen as an extreme example of that. Every homosexual pair that adopts children (and there are a lot!) is, essentially, forgoing spreading their genes directly, and spending the effort that would normally go into that on the genes of some other person. Now, in this day and age, children often get adopted across large distances; but historically, and obviously in nature, adoption would be from geographically and genetically close populations; so it's a form of altruism that can be favored by natural selection. If you unwind back even further, before family was a thing, any tribe members that don't have children of their own have more time to spend watching, feeding and protecting others' children.
Now, you might wonder, why homosexuality rather than asexuality, since the latter would produce the same result? Evolution, due to the mechanisms that drive it, generally takes the path of the least resistance at any given point, even if it results in a very long-winded trek long-term. And it's simpler, from an evolutionary perspective, to "neutralize" the sexual drive by changing its target, than it is to switch it off completely. On top of that, there are some benefits other than children to be derived from sexuality in social species - bonding and mutual assistance, facilitating communication (as e.g. bonobos often use sex) etc.
Exclusive homosexuality analogous to human homosexual relationships is rare in nature. There are animals that are extremely promiscuous and have sex with anything else regardless of its sex, and there are animals that form homosexual relationships in the absence of enough sexual partners, and revert to heterosexual behavior when partners become available.
From a scientific standpoint, there's been alot of theory about an Aunt/Uncle advantage which is similar to a Grandparent advantage as far as it being able to help improve survival through the family of any genes responsible even if it is at the cost of an individual.
Of course, there's also the strong possibility that it isn't purely genetic but a mix of certain genes, which may be linked to other important traits, with a certain environment (possibly even in utero).
The problem with the aunt/uncle theory is the math. A non-breeding sibling would have to enable their siblings to have two additional children (above and beyond the children they would have had anyway) for each child that the non-breeding sibling forgoes having themselves for the strategy to even hit break even, from a genetic point of view.
Because the number of siblings is close to number of children it actually comes to each breeding sibling to have extra two children survive into adulthood. This becomes even less steep if we remember that cousins can also be included in the math.
For example the gay person becomes a village healer and can spent time on that precisely because he/she doesn't have own children to look after.
The hypothesis I put forth (implicitly) is that homosexual genes are still around because of the massive social pressure to have children and to never admit being gay.
Now that this pressure is gone, we could see a huge drop in these traits over the next few centuries.
I don't know how that is supposed to work. What sort of social pressure could possibly produce near-zero fitness impact when it makes you not want to have sex with women, in an environment where the men who do want to have sex with women are like 95% of the population and will happily put enormous efforts into doing that and taking your place? In addition, as I said, given the apparent fitness impact and frequent childlessness of gay men, we should be able to see homosexuality rates plummeting over the past century, but as far as I know, there's no evidence. (Plus the wild animal thing, yeah.) There's something stranger going on. The 'gay germ' hypothesis, as unpopular as it may be, at least adequately reconciles all of the observations.
Maybe you're misunderstanding the parent (or I'm misunderstanding you!). I believe the parent is saying that the genes which predispose somebody to being gay remain in the population, despite their seemingly zero reproductive fitness, because gay people face enormous pressure from their relatives to not be gay and reproduce. And they face this pressure because their family members have a genetic interest in the gay person's offspring and so have evolved to coerce gay family members into having children.
Many animal populations have non-reproductive members. It takes a village to raise a child. In such an extremely social animal as Homo Sapiens, many of our adaptations are social. E.g. it only takes a few men to guarantee another generation, yet 50% men are born in each. Another: we don't die the instant we give birth; we're there (and non-reproductive) for decades afterward, competing for resources. Its the social benefits that allow for this.
Your hypothesis assumes that, historically, all human societies had a massive social pressure against homosexuality. But it contradicts what we know about our history - there were numerous societies that treated it ambivalently (e.g. China, Japan, Native Americans) - and it didn't seem to produce any noticeable effect.
But if the individuals who have the greatest expression or concentration of these genes are having children less frequently (because they are no longer pressured into having children by their relatives/community), then this will act as a siphon for those genes over many generations. That doesn't mean that they will completely disappear, but that these genes would become much less prevalent.
I think homophobia is the reason why non-straight genes are present in the gene pool. It is a strategy for parents and siblings to make sure that their non-straight relatives reproduce despite their natural inclinations.
Just a disclaimer though: this is not at all a justification for homophobia, in the same way that the (mostly) male impulse to violence is not a justification for said violence.
I was raised to always double down on an unpopular idea if I think there's something to it, so here goes:
From the point of view of genetic fitness, homosexuality is not adaptive. So you would think that the genes that contribute to homosexuality would be powerfully selected against, since the number of expected offspring from same sex intercourse is zero.
Yet gay people make up a sizable portion of the population, which is not at all what you would expect. Unless there is some mechanism by which homosexuals have historically had children despite their natural inclinations.
Given that some portion of anti-gay attitudes seem to be oriented toward getting them to "be more straight" (or whatever), it seems possible to me that homophobia (or at least a certain flavor of it) is an adaptation whose purpose is to get family members to pressure a gay person into having offspring, since they would have a genetic interest in those offspring.
But that is an argument about why a certain behavior might exist in humanity. It is not an argument that homophobia is okay or justified. It is not okay.