That theory is even worse than the inclusive fitness one because you offer no mechanism whatsoever to offset the huge fitness penalty.
Sexual imprinting is a highly successful evolved mechanism critical to reproductive fitness which does in fact succeed in the overwhelming majority of cases; in many ways, it is more important than trivial details like ‘eating food’ because at least an offspring which immediately starves to death doesn’t drain parental resources and compete with siblings and the parents can try again! There should be a very good reason why such an important thing, found throughout the animal kingdom in far stupider & less sexually-dimorphic organisms, goes wrong in such a consistent way when other complex behaviors work at a higher rate and fail much more bluntly & chaotically. ‘Random imprinting’ is too weak a mechanism to thwart such a critical device, and doesn’t explain why the errors do not rapidly disappear with general or sex-linked adaptations. (Even as a 5% liability-threshold binary trait, a reproductive fitness penalty of 50%, to be generous to a trait which involves active aversion to procreative sex, would imply it should be far lower now than when it first arose*.)
Further, such a random nonshared environment theory doesn’t explain why dizygotic and monozygotic same-sex twins differ in concordance. (They don’t differ in language, so your example is evidence against your imprinting theory.)
* https://www.researchgate.net/profile/J_Bailey2/publication/21311211_A_genetic_study_of_male_sexual_orientation/links/02e7e53c1a72a8a596000000.pdf gives a low end heritability estimate of 0.31; population prevalence among males is usually estimated ~5% giving a liability threshold of ~-1.64; homosexuality is amply documented for the past 2500 years or so, at least back to the ancient Greeks, which at a generation time of ~25 years, means 100 generations. So assuming a fitness penalty of ‘just’ half and that selection started only 100 generations ago (rather than much further back), we would expect the rate of homosexuality to be less than 1/5th what it is.
To be immune to selection because it’s part of intelligence would imply a strong genetic correlation. Aside from the fact that I am doubtful any such genetic correlation will ever be found (there is no noted phenotypic correlation of homosexuality & intelligence that I’ve heard of), this still has the issue that homosexuality ought to be decreasing noticeably over time: while intelligence has apparently been neutral or selected for over the past few millennia and so hypothetically could’ve slowed the selection against homosexuality, intelligence itself has been selected against for at least a century, so that would accelerate the selection now that there are fitness penalties for both homosexuality & intelligence (by a fair bit, because selection on continuous traits is much faster than selection on rare binary traits).
there is no noted phenotypic correlation of homosexuality & intelligence that I’ve heard of
I’ve heard the raw correlation widely claimed, but I think most people interpret it as measuring closeting. Certainly openly gay men have higher income than straight men.
I’d be inclined to suspect closeting too. The better your ability to support yourself, the less you need to worry about repercussions.
Tangential and possibly relevant: I’ve noticed bisexual women appear to be ridiculously common in high-intelligence nerd communities. I don’t know whether I should associate that with the intelligence or the geek/nerd/dork personality cluster, nor do I know which way the causation goes.
That theory is even worse than the inclusive fitness one because you offer no mechanism whatsoever to offset the huge fitness penalty.
Sexual imprinting is a highly successful evolved mechanism critical to reproductive fitness which does in fact succeed in the overwhelming majority of cases; in many ways, it is more important than trivial details like ‘eating food’ because at least an offspring which immediately starves to death doesn’t drain parental resources and compete with siblings and the parents can try again! There should be a very good reason why such an important thing, found throughout the animal kingdom in far stupider & less sexually-dimorphic organisms, goes wrong in such a consistent way when other complex behaviors work at a higher rate and fail much more bluntly & chaotically. ‘Random imprinting’ is too weak a mechanism to thwart such a critical device, and doesn’t explain why the errors do not rapidly disappear with general or sex-linked adaptations. (Even as a 5% liability-threshold binary trait, a reproductive fitness penalty of 50%, to be generous to a trait which involves active aversion to procreative sex, would imply it should be far lower now than when it first arose*.)
Further, such a random nonshared environment theory doesn’t explain why dizygotic and monozygotic same-sex twins differ in concordance. (They don’t differ in language, so your example is evidence against your imprinting theory.)
* https://www.researchgate.net/profile/J_Bailey2/publication/21311211_A_genetic_study_of_male_sexual_orientation/links/02e7e53c1a72a8a596000000.pdf gives a low end heritability estimate of 0.31; population prevalence among males is usually estimated ~5% giving a liability threshold of ~-1.64; homosexuality is amply documented for the past 2500 years or so, at least back to the ancient Greeks, which at a generation time of ~25 years, means 100 generations. So assuming a fitness penalty of ‘just’ half and that selection started only 100 generations ago (rather than much further back), we would expect the rate of homosexuality to be less than 1/5th what it is.
My guess is that it’s somehow a spandrel of intelligence.
To be immune to selection because it’s part of intelligence would imply a strong genetic correlation. Aside from the fact that I am doubtful any such genetic correlation will ever be found (there is no noted phenotypic correlation of homosexuality & intelligence that I’ve heard of), this still has the issue that homosexuality ought to be decreasing noticeably over time: while intelligence has apparently been neutral or selected for over the past few millennia and so hypothetically could’ve slowed the selection against homosexuality, intelligence itself has been selected against for at least a century, so that would accelerate the selection now that there are fitness penalties for both homosexuality & intelligence (by a fair bit, because selection on continuous traits is much faster than selection on rare binary traits).
I’ve heard the raw correlation widely claimed, but I think most people interpret it as measuring closeting. Certainly openly gay men have higher income than straight men.
I’d be inclined to suspect closeting too. The better your ability to support yourself, the less you need to worry about repercussions.
Tangential and possibly relevant: I’ve noticed bisexual women appear to be ridiculously common in high-intelligence nerd communities. I don’t know whether I should associate that with the intelligence or the geek/nerd/dork personality cluster, nor do I know which way the causation goes.