Evolution and Homosexuality

[ps139]

Before writing my question, I want to make it clear that this thread is not the place to argue about the moral implications of homosexuality. There is a place for discussion of that in the S&C forums.

How does evolution explain homosexual orientations. I do not understand because someone born with a homosexual orientation is not a benefit to the species in the sense that the chances of reproduction are so slim. Basically, my point is, if there is a homosexual gene or something of that sort, wouldn't it be recessive, and would it not have been naturally selected against?

Also, one may argue that in past times, when homosexuals were "in the closet" they often married and had children with women to seem socially acceptable. If this cultural reason is the sole reason that homosexuality can be passed on, would you say that now, when homosexuals are in open relationships with each other, the chance of passing along the gene would be lessened, and we could expect to see many homosexuals now, but the more and more they live together and do not procreate, the rarer people will be who are born homosexual?

 

[Ferahgo-Under-God]

What if, however, homosexuality is not a gene. I just can't see being one because I was "born with it" thats kind of a whack on free will. I believe homosexuals are as they are because they use it to right something in their lives that isn't right with them, and for some reason they believe that is the way out. This could be very different reasons for different people.

 

[Taffsadar]

Well a nice counter question . How do creationists explain that a perfect god creates such horrible sinners?

However if it doesn't have anything to do with genes, then it doesn't have anything to do with evolution either...

 

[Ferahgo-Under-God]

No, I suppose it doesn't really have to do with evolution then does it? And to answer your question it's because he loves us enough to give us free will.

 

[Arnold_Philips]

I'll try to answer to the best of my knowledge, but a lot of it might be wrong....

Homosexuality, from what I can tell, is most likely the result of polygenic inheritance, meaning that it's not a single gene that controls it (like an ON/OFF switch). There are various factors that would have to be satisfied in order for the human to be homosexual. It would be like having to roll a die 25 times and come up with the same number each time.

Assuming this is true, then it explains how homosexuality appears in constant proportions worldwide regardless of color or creed. Every human has the same number of "rolls of the dice" so to speak, and it's just a matter of getting the same number 25 times in a row.

Also, homosexuality might have some advantageous implications. The homosexual is not hindered by mating season, he/she can act as a foster parent in the event of the biological parents' death, and so on.

 

[shenzhou]

[QUOTE=Ferahgo-Under-God]I believe homosexuals are as they are because they use it to right something in their lives that isn't right with them,[/QUOTE]

Obviously that doesn't explain gay sheep:

"Domestic rams display distinct variations in sexual behavior that make them a unique and valuable model to study the biological underpinnings of sexual partner preferences. Most domestic rams are sexually active with females and are classified as female-oriented. However, approximately 8% of rams display sexual partner preferences for other males and therefore are classified as male-oriented (1;2). The male-oriented sexual preference of rams does not appear to be related to dominance or flock hierarchy (3). No early social factors have been identified that can predict or alter sexual partner preference in rams (1;4). Male-oriented rams are not female-like in their sexual behavior. Rather, they execute a typical male copulatory motor pattern that is directed at rams instead of ewes. Sexual partner preference does not appear to be regulated by hormonal status in adulthood. Pinckard et al. (5) demonstrated that castration reduces mounting in both female- and male-oriented rams, but does not alter their choice of sexual partners. Moreover, variations in basal concentrations of testosterone in adult rams do not correspond with differences in mate preference (6)."

Or the fact that homosoexual behaviour is common throughout the animal kingdom. Interestingly this behaviour does not seem to be very heritable, which would suggest that it might not be possible to select against. It could be that the mechanism that determined sexual orientation had a certain error rate, therfore homosexulaity could be an inevitable consequnce of the normal process of brain development. Interestingly the number of homosexual sheep, 8%, is similar to that in humans, ~10% (i think).

Charles E. Roselli, Kay Larkin, John A. Resko, John N. Stellflug, and Fred Stormshak. The Volume of a Sexually Dimorphic Nucleus in the Ovine Medial Preoptic Area/Anterior Hypothalamus Varies with Sexual Partner Preference. Endocrinology. First published October 2, 2003 as doi:10.1210/en.2003-1098.​

 

[revolutio]

I don't really know why homosexuality would appear. Bisexuality has obvious perks in that something doesn't need to rely solely on the opposite sex for sexual gratification.

If have heard it suggested that it might be a genetic response to overpopulation. Though I wouldn't have the foggiest how that would work since overpopulation is a concept humans came up with and not really something genes alone could recognize.

 

[the_malevolent_milk_man]

I think by "response to overpopulation" it is meant that once the population is large enough, it doesn't matter if a small fraction of them are homosexual.

If it is genetic then it would have to be recessive, or a combination of unlikely genes. I can see this as a likely option. Although nothing short of finding the "gay" gene/s would prove it. There are much more important areas that our geneticists need to be working on.

As I see it this question is only important to christians since they have a faction that believes homosexuality to be a sin. As an atheist I couldn't less care if it's genetic, a choice, or psychological because I couldn't care less if you prefer cucumbers or peaches.

 

[Data]

Homosexuality, from what I can tell, is most likely the result of polygenic inheritance, meaning that it's not a single gene that controls it (like an ON/OFF switch). There are various factors that would have to be satisfied in order for the human to be homosexual. It would be like having to roll a die 25 times and come up with the same number each time.

I like this explanation the best. As far as I know, it is definately not a single mutation, and double blind studies have shown there is definately a genetic component.

However many animals have homosexual sex. Our closest relative, the bonobo, does it all the time.

 

[ps139]

As I see it this question is only important to christians since they have a faction that believes homosexuality to be a sin.

Well milkman, you're wrong. I have always wondered about this question because there are a lot of things about evolution I don't understand, this being one of them. As I stated I do not want this thread getting off topic into the morality of it all.

 

[ps139]

I'll try to answer to the best of my knowledge, but a lot of it might be wrong....

Homosexuality, from what I can tell, is most likely the result of polygenic inheritance, meaning that it's not a single gene that controls it (like an ON/OFF switch). There are various factors that would have to be satisfied in order for the human to be homosexual. It would be like having to roll a die 25 times and come up with the same number each time.

Assuming this is true, then it explains how homosexuality appears in constant proportions worldwide regardless of color or creed. Every human has the same number of "rolls of the dice" so to speak, and it's just a matter of getting the same number 25 times in a row.

What are the chances of rolling a die 25 times and coming up with the same number each time? Much much less than 8%, which is what I have heard the estimated human homosexual population to be. I know that your 25 times idea is not exact, I'm just gauging the possibilities. And wouldn't chances of that happening be bred out? For example, in caveman times, would the homosexual really be competing for the woman, or would he not care and spend his energy on other activities?

Also, homosexuality might have some advantageous implications. The homosexual is not hindered by mating season, he/she can act as a foster parent in the event of the biological parents' death, and so on.

That is true but I still do not understand how it could still be in any way genetic, or at least to the degree it is claimed to be (8-10%) this far down the line in human history.

I enjoy this discussion its very interesting, all opinions welcome.

 

[LewisWildermuth]

What are the chances of rolling a die 25 times and coming up with the same number each time? Much much less than 8%, which is what I have heard the estimated human homosexual population to be. I know that your 25 times idea is not exact, I'm just gauging the possibilities. And wouldn't chances of that happening be bred out? For example, in caveman times, would the homosexual really be competing for the woman, or would he not care and spend his energy on other activities?

It would only be bred out if it was a large disadvantage, but since the human (and other animal species) populations are not seriously hampered by a few homosexuals there is no pressure to remove it.

That is true but I still do not understand how it could still be in any way genetic, or at least to the degree it is claimed to be (8-10%) this far down the line in human history.

I enjoy this discussion its very interesting, all opinions welcome.

So you at addolecence made a purposeful decision to be attracted to females?

True, not all of homosexuality is genetic, part of it seems to be, just like many of our other behaviors.

 

[Arnold_Philips]

What are the chances of rolling a die 25 times and coming up with the same number each time? Much much less than 8%, which is what I have heard the estimated human homosexual population to be. I know that your 25 times idea is not exact, I'm just gauging the possibilities.

Yeah, I just pulled a number out of the air.

And wouldn't chances of that happening be bred out? For example, in caveman times, would the homosexual really be competing for the woman, or would he not care and spend his energy on other activities?
That is true but I still do not understand how it could still be in any way genetic, or at least to the degree it is claimed to be (8-10%) this far down the line in human history.

I enjoy this discussion its very interesting, all opinions welcome.

Well, just because something is bad (reproduction-wise) doesn't necessarily mean that it's weeded out. Evolution isn't directional; it only responds to environmental factors. If homosexuality substantially hampered the survivaly of humankind, then someone that didn't give birth to homosexuals would be favored to carry on her genes.
The chances of mutation alone are small, and the chances of a beneficial mutation are even smaller. Factors that effect evolution like mutation and genetic drift aren't drastic or programmed. Just because humans hunted dodo birds doesn't mean that they will automatically develop fangs or something. If one did develop fangs, and it aided in surviving humans, then that would work. But the chances of a dodo bird developing fangs is infinitesimal.
Look at the appendix: it has no function that we know of, yet our bodies retain it. It sometimes causes us harm, but not enough where it those with appendicitis are taken out of the gene pool.

 

[the_malevolent_milk_man]

Well milkman, you're wrong. I have always wondered about this question because there are a lot of things about evolution I don't understand, this being one of them. As I stated I do not want this thread getting off topic into the morality of it all.

How is this important to evolution?

 

[Bushido216]

I'm no expert, but the answer may lie somewhere in the neighborhood of "why do so many people have down symdrome?"

Obviously, DS has no reproductive value, and most organisms with it probably died very quickly. However, if that's the case, why do we still see people with it?

Perhaps it's a common mutation or error in some sequence.


Note: Just to cover my politically correct ***, I do not consider retarded people bad, nor gays. So there!

 

[ps139]

How is this important to evolution?

What I was doing was saying "No, milkman, the only reason I am asking this is not because I want scientific justification that homosexuality is a sin," which you implied was the only reason a Christian would ask this.

 

[pureone]

I'm no expert, but the answer may lie somewhere in the neighborhood of "why do so many people have down symdrome?"

Obviously, DS has no reproductive value, and most organisms with it probably died very quickly. However, if that's the case, why do we still see people with it?

Perhaps it's a common mutation or error in some sequence.


Note: Just to cover my politically correct ***, I do not consider retarded people bad, nor gays. So there!

dS is trisomy 21 I.e. Three chromosomes of number 21. It is not a mutation exactly, and the reasons for it happening are different than those for mutations
http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=190685

 

[pureone]

BtW, if you want to know about any human disease, put it into the OMIM search window.
The first one will probably be the one you want...

 

[seebs]

How does evolution explain homosexual orientations. I do not understand because someone born with a homosexual orientation is not a benefit to the species in the sense that the chances of reproduction are so slim. Basically, my point is, if there is a homosexual gene or something of that sort, wouldn't it be recessive, and would it not have been naturally selected against? [/b]

"recessive" has nothing to do with beneficial or harmful; it just means that the gene only expresses when some other gene isn't present. Blue eyes are "recessive".

Anyway, consider sickle-cell anemia. It's common, not because sickle-cell anemia is such a good thing, but because children who have one gene for it, but not two, are immune to malaria.

It's all about the side effects. It's been hypothesized that homosexuality is an advantage for the family group containing the homosexual, because people without kids are very likely to help their siblings raise their kids, or take the kids on if their parents die.

 

[Bushido216]

dS is trisomy 21 I.e. Three chromosomes of number 21. It is not a mutation exactly, and the reasons for it happening are different than those for mutations
http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=190685

I knew it was an extra chromosome, I just wasn't sure how to express it.

My question is though, is my point still valid? Could homosexuality be constantly recurring for the same reason that other errors in reproduction constantly occur?