Will evolution eradicate homosexuality?

[markyb1888]

I am an amateur studying physics on my own accord purely to satisfy my own curiosity and new to the forum , so please be gentle if i am stating something blatantly obvious or that has been discussed already.

I was not studying this topic but had discussions with someone about DNA and then separately about homosexuality and homosexuality in history.

Basically they questioned how many people were homosexual in the past.

Well i thought that purely from a scientific and evolution point of view being homosexual is a genetic flaw , i mean our existence is down to humans reproducing and obviously if people of the same sex are together they are not reproducing.
Evolution and natural selection tends to iron out a lot of flaws so i thought surely if flaws are generally being ironed out like this then it must have been more flawed in the past (a higher percentile of people could have been homosexual?).

Then i thought about the social side of this and there are many points in the past where homosexuality was an outright taboo or illegal and is still illegal in many countries today.
As a result people must have been feeling forced into trying to "act normal" and have partners of the opposite sex and have offspring which would be passing these "flawed" genes on to their offspring.

As i said i understand homosexuality is still illegal in many countries today but it is vastly more acceptable on a global scale than it was say 50 years ago , You would expect if current trends continue that homosexuality is only going to be accepted more and more and people will feel free to be open about this and cohabit with members of the same sex instead of trying to "act normal" and have an opposite sex partner and produce offspring.

In this scenario surely less homosexual people will have offspring and as a result these genes will decrease exponentially. I understand there are other ways for people to have offspring and IVF etc and as a result people in same sex relationships could still have offspring but obviously this is much harder to do than just having intercourse so surely a fewer percentage of offspring would have these genes?

So basically I am asking Will evolution eradicate homosexuality ?
Will society openly accepting homosexuality mean there is no need for people in this situation to "live a lie" and basically mean they reproduce less and these genes start to disappear ?

P.S. I'm neither homosexual or homophobic , i just found the subject interesting from an evolutionary standpoint.

 

[Ryan_m_b]

Whilst we don't know the exact cause of sexuality we are certain that it isn't as simple as a gay gene. It is far more likely that homosexuality (along with every other sexual variant) is a by-product of our ability to possesses a sexuality. Therefore it will not be "evolved out" unless our capacity to have a sexuality disappears.

 

[markyb1888]

Thanks for the reply Ryan , I did not understand this and will go read up on some of this. Am i wrong is saying though that everyone has the ability to possesses sexualities but only some people will be homosexual and therefor their genetic makeup could be a factor still in determining this?

 

[Ryan_m_b]

Thanks for the reply Ryan , I did not understand this and will go read up on some of this. Am i wrong is saying though that everyone has the ability to possesses sexualities but only some people will be homosexual and therefor their genetic makeup could be a factor still in determining this?

Not everyone, some people are born asexual. The reasons for variation in sexuality are largely unknown but I doubt it is genetic as there are many cases of monozygotic twins that have different sexualities. There has been a lot of study on this topic ranging from examining the epigenetics (I.e. a list of which genes are on and which are off) of both the person and their mother, various factors of development such as hormone levels and social/psychological reasons. For a good summary I would advise you read this http://en.wikipedia.org/wiki/Biology_and_sexual_orientation" .

 

[mishrashubham]

Whilst we don't know the exact cause of sexuality we are certain that it isn't as simple as a gay gene.

Exactly, it is not as simple as that. Phenotypes often have very complex relationships with their genotypes. A single gene may be responsible for multiple phenotypes and a single phenotype is almost never the result of a single gene. And when it comes to behavourial patterns, things can get complicated, since developing a one to one relation between behaviour and genes is pretty difficult. Homosexuality as a trait could be a byproduct of the various complex social interactions that our brain is made to cope with. It could also be influenced by epigenetics.

 

[KattyGenovese]

I'd say that Hamilton's Rule applies here, for the same reasons that altruism remains a behavioral trait in humans. Should an organism reduce its own reproductive fitness, it nevertheless would pass on its genes (since relatives often share the same genes) if the benefit towards their immediate kin and increase in overall fitness outweighs the loss of individual fitness.

At least this explains the behavior of some animals (e.g., the evolution of worker bees that do not reproduce). Humans tend to have complex confounding cultural aspects however.

 

[Evo]

I think the OP doesn't quite understand how natural selection works, as well as not understanding that an individual's sexual preference is too random in the human population to be selected against.

Also, from a historical perspective, homosexuality has gone in and out of acceptance socially. For example, it was widely accepted among the Celts.

 

[markyb1888]

I think the OP doesn't quite understand how natural selection works

I probably could do with reading more into it and will do , as i said i really am an amateur who has/is developed an interest in science so i will have a lot of gaps.

For a good summary I would advise you read this http://en.wikipedia.org/wiki/Biology_and_sexual_orientation" .

Thanks Ryan i will read this.

 

[Evo]

I probably could do with reading more into it and will do , as i said i really am an amateur who has/is developed an interest in science so i will have a lot of gaps.

Try this video, so simple, explains natural selection.

 

[markyb1888]

Thanks Evo :)

 

[Evo]

Posts have been deleted that were not scientifically accurate and responses to those posts.

 

[MarcoD]

I agree that something like a gay gene doesn't exist, and probably homosexuality is a byproduct of the complex human geno- and phenotype.

Still, if you look at it from a Darwinistic perspective, there's one possible thing overlooked in the question. No doubt, homosexuality is bad for the survival of the DNA of an individual. But why couldn't a limited degree of homosexuality in a society be good for the survival of that society?

 

[Ryan_m_b]

I'd like to echo Evo's post and ask everyone to stick to researched science rather than personal speculation. I'm sure everyone can appreciate that this is a topic that attracts a lot of armchair evolutionary biologists.

I agree that something like a gay gene doesn't exist, and probably homosexuality is a byproduct of the complex human geno- and phenotype.

Still, if you look at it from a Darwinistic perspective, there's one possible thing overlooked in the question. No doubt, homosexuality is bad for the survival of the DNA of an individual. But why couldn't a limited degree of homosexuality in a society be good for the survival of that society?

MarcoD if you have any scientific backing from that please provide it, otherwise it is far too speculative.

I probably could do with reading more into it and will do , as i said i really am an amateur who has/is developed an interest in science so i will have a lot of gaps.
Thanks Ryan i will read this.

Look up genetic drift, gene flow and mutation as well ;)

 

[MarcoD]

I am not speculating, I am pointing out a weakness in the argument that homosexuality should eradicate itself.

The scientific evidence is an ant society. Lots of ants are not involved in procreation, but that doesn't hurt the survival of that society.

I.e., Darwinism doesn't always apply to the survival of the individual solely.

 

[Ryan_m_b]

I am not speculating, I am pointing out a weakness in the argument that homosexuality should eradicate itself.

The scientific evidence is an ant society. Lots of ants are not involved in procreation, but that doesn't hurt the survival of that society.

I.e., Darwinism doesn't always apply to the survival of the individual solely.

This is an example of http://en.wikipedia.org/wiki/Kin_selection" for which there is little evidence in human sexuality. When I asked for evidence it was along the lines of "where is the evidence for how this phenomenon applies to homosexuality" rather than evidence of the phenomenon.

 

[MarcoD]

This is an example of http://en.wikipedia.org/wiki/Kin_selection" for which there is little evidence in human sexuality. When I asked for evidence it was along the lines of "where is the evidence for how this phenomenon applies to homosexuality" rather than evidence of the phenomenon.

I also doubt that there have been many studies on that regarding homosexuality. But the burden of proof is on the original poster since he makes an assumption. He has the obligation to show that that assumption, which presupposes no kin-selection, is correct.

In an odd twist, one might claim that homosexuality might be exactly that, since it didn't eradicate itself in the last couple of thousand years.

 

[Ryan_m_b]

I also doubt that there have been many studies on that regarding homosexuality. But the burden of proof is on the original poster since he makes an assumption. He has the obligation to show that that assumption, which presupposes no kin-selection, is correct.

In an odd twist, one might claim that homosexuality might be exactly that, since it didn't eradicate itself in the last couple of thousand years.

This is something that has been studied, just type in "Kin-selection AND homosexuality" into pubmed, webofsci or google scholar. The evidence isn't there that there homosexuality is a product of kin-selection.

 

[mishrashubham]

...since it didn't eradicate itself in the last couple of thousand years.

In order to be eradicated by natural selection, homosexuality needs to be an heritable trait. But we don't exactly know how much of it is genetic.

 

[MarcoD]

This is something that has been studied, just type in "Kin-selection AND homosexuality" into pubmed, webofsci or google scholar. The evidence isn't there that there homosexuality is a product of kin-selection.

I stand corrected, it has been studied. At the same time, I googled it -as you suggested- and found evidence which also claim the contrary. So, I would say the evidence is out, either way.

(http://www.news-medical.net/news/20100205/Kin-selection-hypothesis-may-explain-homosexuality-from-an-evolutionary-point-of-view.aspx" )

Moreover, these are not the studies I expected. If I think about it, with a glass of wine, I would postulate an hypothesis that homosexuality gives an advantage to a society because of a) an added unique perspective to that society, b) lives dedicated to art and/or science, c) the manner in which a society learns to deal with 'others.' (I.e., not because it gives the direct relatives a Darwinistic advantage.)

In short, maybe the Romans chopped off other people's heads because the other society never reached the advantage of having learned how to deal with puzzling other-beings. (The other society stood still in becoming more complex.)

I personally believe it is just a result of the complex pheno- and genotype, but the above hypothesis might be true.

 

[Ryan_m_b]

I stand corrected, it has been studied. At the same time, I googled it -as you suggested- and found evidence which also claim the contrary. So, I would say the evidence is out, either way.

(http://www.news-medical.net/news/20100205/Kin-selection-hypothesis-may-explain-homosexuality-from-an-evolutionary-point-of-view.aspx" )

Moreover, these are not the studies I expected. If I think about it, with a glass of wine, I would postulate an hypothesis that homosexuality gives an advantage to a society because of a) an added unique perspective to that society, b) lives dedicated to art and/or science, c) the manner in which a society learns to deal with 'others.' (I.e., not because it gives the direct relatives a Darwinistic advantage.)

Whilst there are studies that claim to support the kin-selection hypothesis I would say the case has not been made to consider it a candidate. As for your musings how would you explain homosexual behaviour in animals?

EDIT: Actually don't answer that, we should keep conversation to mainstream science. Not personal theories.

I personally believe it is just a result of the complex pheno- and genotype, but the above hypothesis might be true.

Judging by what we know now I would tentatively accept the hypothesis that the evolution of homosexuality is as a by-product of our capacity to have a sexuality and it hasn't been selected against because the advantage strongly outweighs the disadvantage.

 

[nobahar]

I may have missed it, but I don't think anyone has argued that it doesn't have to be beneficial. Phenotypes that are a product of multiple genes can persist in the population, whether benign or detrimental, the individual genes that may contribute to th phenotype may be beneficial by contributing, solely or in conjunction with other genes, to other phenotypes. There doesn't have to be a 'beneficial' role the phenotype plays, it can persist in a population 'off the back of' other phenotypes to which the genes that contribute to homosexuality also contribute. I think that is a possibility.

 

[Ryan_m_b]

I may have missed it, but I don't think anyone has argued that it doesn't have to be beneficial. Phenotypes that are a product of multiple genes can persist in the population, whether benign or detrimental, the individual genes that may contribute to th phenotype may be beneficial by contributing, solely or in conjunction with other genes, to other phenotypes. There doesn't have to be a 'beneficial' role the phenotype plays, it can persist in a population 'off the back of' other phenotypes to which the genes that contribute to homosexuality also contribute. I think that is a possibility.

Indeed, neutral and phenotypic traits can be by-products of advantageous ones.

 

[Jobrag]

I can't quote a source but years ago I read a piece that speculated that; if there was a gene that inclined men to homosexuality (reproductive disadvantage) it might give women some kind of reproductive advantage, thus ensuring that the gene survived.

 

[Ryan_m_b]

I can't quote a source but years ago I read a piece that speculated that; if there was a gene that inclined men to homosexuality (reproductive disadvantage) it might give women some kind of reproductive advantage, thus ensuring that the gene survived.

That isn't very likely. A single gene governing sexuality would be easy to spot, not only that but I highly doubt that a single type of protein could elicit such a massive aspect of personality. Also what about people who don't fit into neat little boxes like bisexuals, pansexuals, asexuals etc? Lastly how would such a gene explain homosexuality in women?

If this were to be true and we ignored all these problems then we would easily be able to spot inheritable homosexuality as the demographic of gay men would resemble autosomal dominant or recessive patterns which we don't in fact see.

 

[bobze]

A lot of what determines sexuality occurs in the womb, in the processes of masculinization and feminization of the brain. As others have pointed it, this means that some aspects of sexuality would be "invisible" in terms of Darwinian fitness.

As others have pointed also, the "incorrect" question is "what benefit to fitness does this trait have"?. Like it was pointed out (Ryan and someone else I believe) traits can "piggy-back" through generations and get "free rides" even though they themselves (or better determinants of them when they are multifactorial) maybe maladaptive.

There has been lots of speculation on ways that homosexuality could be beneficial from a family group perspective (such as having extra-siblings around to help in child rearing, think ants again) but I find these hypothesis to be extremely speculative and rather flimsy in nature. Firstly it should be considered that human sexuality isn't a dichotomy like many suppose. It exists on a spectrum where "strict" heterosexuality and "strict" homosexuality exist on the ends of said spectrum, with a myriad of people existing in between (whether society conditions most of them to admit it or not). Secondly, and even more important I believe, is the basis in "homosexuality" in men and women is very probably a "different mechanism".

There have been a couple different studies that have shown being the last in the line of brothers imparts a greater correlation to being a homosexual male. The fetal trophoblastic tissue is an invasive tissue and goes to great lengths to "fool" the maternal immune system. The thought on this correlation is that the maternal immune system gets 'better' at detecting masculine (expressing a Y-chromosome) invasive tissue (specifically those expressing a more masculine pattern of androgens) and interferes with the process of masculinization of the male brain. Take it with a grain of salt however, because for every case you can find of a 5th brother who is homosexual, you can surely find a single male child raised in a very "masculinized" household who is also a homosexual. Obviously to me then, its not a simple or single mechanism for either sex or even within those sexes.

I suspect the reason homosexuality hasn't been "weeded out" by selection is as others have suggested. Its a complex phenotypic trait (sexuality) much of which is determined outside of the just "genes=phenotype" paradigm (were not pea plants unfortunately). And things which have a genetic component (such as the womb environment) don't have "risks" which outweigh "rewards" from a selection point of view enough to merit negative selective value.

 

[nobahar]

A lot of what determines sexuality occurs in the womb, in the processes of masculinization and feminization of the brain... this means that some aspects of sexuality would be "invisible" in terms of Darwinian fitness.

This is probably stupid, but why would this be exempt from Darwinian fitness? My reasoning is that, IF homosexuality is a disadvantage in reproduction and gene propagation, then natural selection would favour genes that prevent feminisation of a male brain. The mother who has this gene would have a good chance of passing the gene to the baby, who would carry the gene into future generations, even if they are male, they can still propagate the gene (I think). A female whose genes do not favour prevention of the feminisation of a male brain, is more likely to produce homosexual males, leading to a reproductive disadvantage. My understanding is that the womb environment can be manipulated by the genes of the mother and the baby, and since 1/2 of the babies genes are from the mother, the womb environment provides the opportunity for natural selection to occur.

Am I correct in assuming that the argument about being ""invisible" to Darwinian fitness", is based on environmental factors that are not consistent between generations, those that are highly variable? Because I may be wrong, but since genes interact with the environment, and their propagation are influenced by the environment, then a consistent environmental factor would influence the fitness of a gene. If a gene predisposes someone to a particular phenotype in the presence of environmental factor A, and this phenotype is a disadvantage, then the gene would be selected against if environmental factor A occurred in every generation; if factor A occurred sporadically, it would lead to the disadvantageous phenotype only occasionally, and the gene will survive. This was my understanding, admittedly the example is a little simplistic.

There have been a couple different studies that have shown being the last in the line of brothers imparts a greater correlation to being a homosexual male. The fetal trophoblastic tissue is an invasive tissue and goes to great lengths to "fool" the maternal immune system. The thought on this correlation is that the maternal immune system gets 'better' at detecting masculine (expressing a Y-chromosome) invasive tissue (specifically those expressing a more masculine pattern of androgens) and interferes with the process of masculinization of the male brain.

This obviously debunks my above argument about not wanting to feminise the male brain. I wonder why this happens?

 

[J-Girl]

how is homosexuality a genetic trait though? sorry i saw this post and it just interested lol. lots of people know they are gay their whole lives, and others don't "turn" gay until they are 50. how does anybody prove that its down to biology and not just a state of mind?
also..:P, i wouldn't say homosexuality is a flaw or anything, if anything, lots of countries are overpopulated.

 

[Ryan_m_b]

how is homosexuality a genetic trait though? sorry i saw this post and it just interested lol. lots of people know they are gay their whole lives, and others don't "turn" gay until they are 50. how does anybody prove that its down to biology and not just a state of mind?
also..:P, i wouldn't say homosexuality is a flaw or anything, if anything, lots of countries are overpopulated.

Nobody turns gay at any point, sexuality is a spectrum (and not even a linear one). People who live a heterosexual life until they are 50 and then live a homosexual life do so as a result of society. In reality they were always that sexuality but were forced to hide it because it was socially unacceptable, sometimes to the point of being illegal.

 

[J-Girl]

i think this one is really up to opinion? no disrespect intended, but i just don't see how it can be generalized like that

 

[Ryan_m_b]

i think this one is really up to opinion? no disrespect intended, but i just don't see how it can be generalized like that

It's not just opinion, there is a huge wealth of research that has been devoted to homosexuality in a range of fields. Here is just a summary from wikipedia http://en.wikipedia.org/wiki/Biology_and_sexual_orientation. Current evidence/observations strongly suggest that sexuality is a product of nature over nurture.