Is the existence of homosexuality incompatible with evolution?

So why wouldn't being "half gay" be favored over being "fully gay"? Seems having two copies of one gene would quickly be selected out in favor of only having one copy of the gene. And have scientists traced gayness to double genes anywhere? Seems it would be something easily detectable.

 

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So a person who eats carrots but sometimes prefers ice cream is confused? Such definitions would seem to define most people as confused, when in fact they just have different preferences and desires than most people.

 

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Nope..a person who ONLY ate what they disliked and never ate what they liked--that'd be confused. People who liked both would technically be called "bisexual"..

 

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FYI, not all male homosexuality is the result of genes. There is the well-known phenomenon of fraternal birth order that plays a role as well. But according to research, being the youngest of many brothers accounts for only 1 in 7 gay males:


How many gay men owe their sexual orientation to fraternal birth order?
Cantor JM, Blanchard R, Paterson AD, Bogaert AF.
Source
Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
Abstract

"In men, sexual orientation correlates with the number of older brothers, each additional older brother increasing the odds of homosexuality by approximately 33%. However, this phenomenon, the fraternal birth order effect, accounts for the sexual orientation of only a proportion of gay men. To estimate the size of this proportion, we derived generalized forms of two epidemiological statistics, the attributable fraction and the population attributable fraction, which quantify the relationship between a condition and prior exposure to an agent that can cause it. In their common forms, these statistics are calculable only for 2 levels of exposure: exposed versus not-exposed. We developed a method applicable to agents with multiple levels of exposure--in this case, number of older brothers. This noniterative method, which requires the odds ratio from a prior logistic regression analysis, was then applied to a large contemporary sample of gay men. The results showed that roughly 1 gay man in 7 owes his sexual orientation to the fraternal birth order effect. They also showed that the effect of fraternal birth order would exceed all other causes of homosexuality in groups of gay men with 3 or more older brothers and would precisely equal all other causes in a theoretical group with 2.5 older brothers. Implications are suggested for the gay sib-pair linkage method of identifying genetic loci for homosexuality."


How many gay men owe their sexual orientation to f... [Arch Sex Behav. 2002] - http://www.ncbi.nlm.nih.gov/pubmed/11910793

 

It's difficult to imagine something so obviously disadvantageous to reproduction and costly of resources surviving as a common spandrel in all human cultures (and in many other mammals and birds) - both the connection and the benefit would have to be very strong.

It's far more likely that whatever in the genome tends to homosexual orientation is of direct benefit to its own survival and reproduction somehow.

That would be among the likely genetics-based aspects of the situation.

 

You can't select to only have one copy of a gene. You get one from your mother and one from your father. You would need to evolve a complicated behavioral mechanism (and detection mechanism to make men and women who have the same copy averse to one another...worse there are plenty of genes that have the same issues, and it gets even more complex is you need breeding pairs to somehow innately know the genetic profile of a mate so they can avoid the expression of deleterious recessive traits in offspring.

Take the sickle cell gene. If you have one copy, you get a resistance to malaria. If you have two copies you have sickle cell anemia and (in a state of nature) are likely to die younger due to blood clots and organ damage.

We know with reasonable certainty that we evolved the trait because malaria is dangerous, and yet evolution has not weeded out the possibility of having two copies of that gene.

Evolution is not an intelligent process, though. It doesn't "see a problem" and "try to solve it." It takes random mutations that happen to cause net improvements in an organism's survivability, and it makes it highly likely those will survive and that net negative mutations will be bred out in time. If a mutation is 75% beneficial and 25% harmful, that's one that is likely to make it. Because it's random though, it could well be that there is a solution to the "two copies bad" problem...but no mutation has ever randomly hit upon that theoretically possible improvement. (Throw that into the column of "if we evolved to walk upright, why do so many people still suffer knee and back problems as a result?" or "why hasn't evolution given everyone 20/20 (or better) vision?")

 

the trait/genes would be in the heterosexual gene pool, unexpressed presumably, as heterosexual couples clearly produce gay offspring, gay people dont need to pass it on, however gay people do reproduce aswell, thus that provides a second way in which the trait is passed on.
However I want to acknowledge that other credible theories have been mentioned in the thread, I am unable to pass judgement on which holds superior merit.

A valid point, but I do wonder about human evolution and the strength of selective pressures that would be required. To what extent are we under natural selection pressures. Ofcourse I am in danger here of focusing on current human evolutionary procceses centred in modern civilisation. Pre-civilisation, the majority of our evolutionary history, is far different and I dont know much regarding this, making it difficult for me to visualise other theories and selection pressures that may have been relevent.

Perhaps

Spandrels, independent of the content of this thread provide a powerful concept in evolutionary theory, that every trait is not directly selected for by natural or sexual selection is fascinating imo.

 

We must also factor in the point that gay people have had kids, do have kids and will continue to have kids. Perhaps now access to relatively free expression of a homosexual lifestyle could have an effect in the future, what with the reduction of faux heterosexual coupling, but I doubt it. There are now more options for having kids than ever before

 

I'm not buying it. Geneticists have found no double genes in gay people. There isn't even a single gene traceable to being gay. It involves a complex of genes.

 

Ahh..the old "gay people are secretly having heterosexual sex" theory. Yeah, if that were true, that would explain how gay genes get passed on to heterosexuals as unexpressed genes. But it's not the case. There are far to many heteros who have gay kids and yet who are NOT the children of a gay parent. Spandrel is a nice word, but it doesn't seem to apply in this case.

 

no, I only mentioned that as an aside, it isnt a necessary for the spandrel theory

Heterosexuals also carry the genes as they produce gay offspring, Gay genes are in the heterosexual population.

Hey

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thats my point too , see previous posts

That I cant say and I havnt seen anything as of yet in this thread to help me draw definitive conclusions, when I get the time I will do some research on this matter, Its a very interesting topic.

 

Still doesn't make sense to me. People who eat carrots instead of ice cream because they know that carrots are better for them aren't confused, they've just made a decision. Even if they like ice cream.

More applicable case in point - know a woman who was heterosexual until she was about 34, then met a woman she hit it off with. Now she's bisexual. She's not confused; she knew exactly what she wanted, and with whom.

 

The woman went from being unconfused about wanting men to being unconfused about wanting women. I wouldn't call that "having sex with someone you don't like having sex with" (a state of confusion). I'd call it "turning bi". Probably happens more often that we think.

As far as your analogy, it doesn't fit what we're talking about. People don't have sex because it is good for them like eating carrots. Normally they have sex because they enjoy it. If someone is always having sex that repulses them, and deny themselves the sex they'd truly enjoy, then they are confused. EOS..

 

Still doesn't make sense. You're saying this gay gene is unexpressed in heteros and yet still expressing itself to the extent of conferring some mysterious survival advantage on them. Either a gene expresses or it doesn't. I don't see how it could do both at the same time.

 

A concept best approached with wariness.

Start with this: as Dennett and others have pointed out, the architectural spandrel, the feature whose name was borrowed by Gould for his proposed concept, is not itself a spandrel in Gould's sense. Gould was unaware of the circumstances in which spandrels came to be, and what they were for, and mistakenly assumed they were useless and arbitrary, present only by the whim of accident and maintained only because they did no harm.

But even if spandrels do exist as major features of some evolved beings, in Gould's terms, they would seem to be most unlikely at the ground of reproduction - the very pivot of evolutionary advantage. If genes with alleles more strongly abetting homosexuality exist, they exist in the face of obvious and significant and direct reproductive cost. That's about as strong as selection pressure gets.

 

I am moving further and further away from areas which I know something about, but I will provide some attempt. My best would be that the homosexual genes can remain unexpressed but the "mysterious" genes that confer a net postivie advantage on darwinian fitness can be expressed. Essentially that the genes are tied due to constraints and are therefore present in the genome, but that their expression isnt tied. To be fair, I have no clue if that is theoretically plausible?

Iceaura

I am a little confused, is the first paragraph solely refering to the origins of the term, for even if gould's architectural observations were flawed, it has no real impact on the merit of the concept in evolution.
Spandrels are in themselves not necessarily accidents at all, just because they may be undesirable on their own, they may have been selected for indirectly, a measured cost.
Least likely at reproduction? interesting idea....but I have already raised my concerns regarding human evolutionary pressures. However, perhaps it indicates what you already said, that for a spandrel to exist at reproduction would require a powerful advantage tied trait.

Perhaps this is enough on this theory. It wasnt my intention for it to become so dominating in the discussion and this thread should not be hijacked to discuss the potential role of spandrels in evolution.

 

It has, hopefully, the impact of a warning. The type specimen of a "spandrel', the source of the label of the entire category, chosen to exemplify the category and illustrate the concept by one of the finest intellects in the field of theoretical evolutionary biology and its explications, was a mistake. So be careful.

Can you demonstrate even the existence of spandrels - any spandrels - in any evolved organism? It's not easy. It's possible they don't exist at all, in any useful sense here on this thread (i.e. as anything other than an error of framing or focus).

If the invocation of the term is in essence a more focused way of stating a null hypothesis in evolutionary research, that's one thing. If it's more than that, we find it difficult to pin down exactly what is or is not a spandrel - either in theory or in fact, but notably in fact, where the notion is far too convenient for safety in muddled or complicated situations. If the choice is between "that's a spandrel" and "we don't know", take the second option every time.

In particular, significant selection pressures on homosexuality in humans are obvious. So at first glance it's a very bad candidate for spandrelhood. It's too significant for backwater viability, too common and universal to be an accident.

 

RE: Title

Is the existence of homosexuality incompatible with evolution? What does it matter? What are the impacts?

 

OK. But by that definition you have to grant that there are also people who have sex with a gender they don't prefer for what they consider good reasons (they want a family, they want the financial security or stability that marriage brings.) Sounds like the opposite of "confused."

 

It is expressed in both. In a woman, for example, it makes them more attracted to men. In a man, it also makes them more attracted to men.