homosexuality and evolution

[Muzna]

According to some scientists homosexuality is heritable. In other words, the tendency to prefer your own gender to the opposite in mate choice is influenced by genetic factors. This is a controversial topic for many reasons but for the sake of argument let us consider the possibility that it is true. Explain why heritable homosexuality poses a problem from an evolutionary viewpoint and what are some possible explanations as to how homosexuality could be adaptive.

[Mokele]

Why does this sound like the essay question from someone's homework?

[iNow]

I agree, this sounds like homework. Muzna - It's okay to ask for help with your homework, that's not the issue. Do you have any ideas on where to start?

 

For example, most people see evolution as the passage of genes from one generation to the next. Why would homosexuality seem to be a problem in this regard?

 

Since your question grants as a given that homosexuality is genetic, it must provide some sort of benefit in terms of genetic fitness. What might that be?

 

 

What ideas do you have? You get the ball rolling, people here will step-up and help you to fill in some gaps.

[CDarwin]

Since your question grants as a given that homosexuality is genetic, it must provide some sort of benefit in terms of genetic fitness. What might that be?

 

Or it may be linked to another trait or traits that confer some fitness.

[mooeypoo]

I'm sorry, but last I checked, the question of nature vs. nurture was not, just yet, clear.

 

Before we even get into the "is it or isn't it hw" problem, I must ask -- Which scientists claim it is hereditary, and where are these claims posted?

[iNow]

Moo,

 

Respectfully, I want to point out that your question is pretty much completely off-topic. The OP explicitly stated that the genetic basis of it was taken as given.

 

I agree with you that there is no final consensus yet, and that both nature and nurture play complex roles. However, it has nothing to do with the issue raised in the OP, or the questions asked based on that premise.

 

According to some scientists homosexuality is heritable. In other words, the tendency to prefer your own gender to the opposite in mate choice is influenced by genetic factors. This is a controversial topic for many reasons but for the sake of argument let us consider the possibility that it is true.

 

Since there is no conclusive evidence that it's NOT genetic (it's not like he's here arguing for a perpetual motion device), perhaps we can explore the issue.

 

Or, maybe I'm just wasting my time since they haven't been back to clarify since the initial responses. That is seeming more and more likely.

 

 

More available here:

http://en.wikipedia.org/wiki/Biology_and_sexual_orientation

[mooeypoo]

Moo,

 

Respectfully, I want to point out that your question is pretty much completely off-topic. The OP explicitly stated that the genetic basis of it was taken as given.

 

Yea.. that's what I'm having problems with. I don't tjhink it's off topic to check the "ingredients" of your question. If the premise that leads to the conclusion (or what conclusion you wish to examine in the question given) is flawed, then the question itself is flawed.

 

If this is a thought experiment -- as in, "what if it's proven that homosexuality is hereditary.." then we can carry on, I guess, by examining this. But how is this any different than starting a question with something like "It is said that evolution is having a baboon out of a horse.." and then asking a question about it? If the premise is false, what good is the final question *based* on that premise?

 

 

I agree with you that there is no final consensus yet, and that both nature and nurture play complex roles. However, it has nothing to do with the issue raised in the OP, or the questions asked based on that premise.

I disagree, but in all honesty, I might've misunderstood it, and if so, I take all I said back. I just thought it was weird that such a strong premise is presented, when the premise is not really accepted science ..

 

 

Since there is no conclusive evidence that it's NOT genetic (it's not like he's here arguing for a perpetual motion device), perhaps we can explore the issue.

I semi agree. If this is a thought-experiment (as I said above), then sure, we can explore it, but that's not quite how the question was presented, and I think it's important we recognize that it's unclear.

 

Personally, btw, I think it *is* more hereditary than social, but that's my own personal opinion, unsupported by anythingother than my own personal opinion and experience. I recognize that it's *not* valid to state anything out of these above "factors", so I don't *state* anything as a basic premise when I ask those type of questions...

 

I.. hope I managed to convey my point here I didn't mean to start a bashfest over this or to take away from the discussion, but seeing as most posts asked about whether or not this is hw or not, it struck me that the premise itself is faulty (because it's absolute, not because it might or might not be true), and this is not a good way to start a debate -- and an even worse way to start a homework problem.

 

 

~moo

[iNow]

We definitely agree on pretty much everything here, especially about trying to start a discussion based on a questionable premise. I also agree that this premise seems pretty solid (not that questionable), so I'll stop acting like you're my girlfriend where I tend to carry on an argument over nothing for no apparent reason and then get myself into even more trouble.

[mooeypoo]

Haha

 

I was, actually, about to apologize. I seemed to have missed the sentence you've bolded, which seems to change the meaning of this question from a firm statement to a "thoguht experiment" like I suggested this might be.

 

Apologies. I still hold my view that those arguments are hard to make with a "firm statement" on the beginning of them, but they take a completely different turn when that is presented as a non-validated issue meant for thought experiment only.

 

I take it back. Carry on..

 

~moo

[Muzna]

@ iNOW

In biology, we learn that the "survival of the fittest" depends on how many offsprings they can pass on their genes too. Homosexuals can't pass there genes to anyone, and thus that provides a large hurdle in any gene theory of homosexuals but then again there are numerous genetic possibilities that would allow for homosexuality. I will only give one example of this: It might be possible that the homosexuality gene only works in a recessive way. Persons who are heterozygous for that gene, remain heterosexual and reproduce. Only when two heterozygous people for that gene, get children 1 in 4 of the children can be recessive and will thus develop homosexuality. This way that gene need NOT become extinct because it is being transmitted through the 'normal reproducing' heterozygotes but thats not the point since as u mentioned above, the fact that homosexuality is genetic is granted as a given in my question so theres no point in talking about whether it is or it is not genetic....what im having problems with is HOW could that be proven beneficial or "adaptive" in terms of genetic fitness...i thought n did some research but still wasnt able to come up with any solid reasons to prove that.

[mrburns2012]

@ iNOW

In biology, we learn that the "survival of the fittest" depends on how many offsprings they can pass on their genes too. Homosexuals can't pass there genes to anyone, and thus that provides a large hurdle in any gene theory of homosexuals but then again there are numerous genetic possibilities that would allow for homosexuality. I will only give one example of this: It might be possible that the homosexuality gene only works in a recessive way. Persons who are heterozygous for that gene, remain heterosexual and reproduce. Only when two heterozygous people for that gene, get children 1 in 4 of the children can be recessive and will thus develop homosexuality. This way that gene need NOT become extinct because it is being transmitted through the 'normal reproducing' heterozygotes but thats not the point since as u mentioned above, the fact that homosexuality is genetic is granted as a given in my question so theres no point in talking about whether it is or it is not genetic....what im having problems with is HOW could that be proven beneficial or "adaptive" in terms of genetic fitness...i thought n did some research but still wasnt able to come up with any solid reasons to prove that.

 

Bees experience a similar problem: sterile worker bees can't reproduce (obviously), but they're adaptive. People have done extensive studies trying to explain why sterile worker bees are adaptive. I'm not suggesting that there's an absolute answer for your assignment, but you could always extrapolate reasonable ideas from animal studies, like ones of honey bees. Another related question is why sterile grandparents (e.g. postmenopausal females, or most males, not including Hugh Hefner) might be adaptive.

Edited February 18, 2009 by mrburns2012

[sciencetoyboy]

Could it be that this is evolutionary behavior which stems from harem type groups of primates where a resistive gene for homosexuality could do well by way of a male primate being allowed to stay with the group because he wasn't a threat to his brother the dominant male, and helping to look after his brothers genes by staying within the group.

just a thought.

[iNow]

In biology, we learn that the "survival of the fittest" depends on how many offsprings they can pass on their genes too. Homosexuals can't pass there genes to anyone, and thus that provides a large hurdle in any gene theory of homosexuals but then again there are numerous genetic possibilities that would allow for homosexuality.

 

<...>

 

what im having problems with is HOW could that be proven beneficial or "adaptive" in terms of genetic fitness...

Hi Muzna,

 

I'm glad you came back. I wasn't sure that you would since we hadn't heard from you in a few days, but welcome.

 

Okay, I didn't formally study biology, so note that I am simply an interested layman in this. However, I will pose some ideas, and hope that the community can discuss them, add more of their own, and correct any where I might be mistaken.

 

The confusion really rests on an oversimplification, and even misunderstanding, that "only individuals who are able reproduce will contribute offspring to the next generation," and that "since homosexuals don't tend to reproduce, their genes can't get passed on." That's really not the case.

 

Sex and evolution isn't split down such clearly divided lines like that, and we must account for changes in allele frequency over time for the entire population... basically, think of this at the population level instead of the level of the individual. That answers the logical part of how homosexuality has not been removed from the gene pool, since something can benefit the entire population without necessarily making clear benefit at the level of the individual. Evolution is not all about "passing on MY genes," it's often about "passing on the genes of my GROUP/PACK/FAMILY." Remember that evolution acts on populations as well, and that will help in understanding this.

 

 

To start things off, one speculation about homosexuality is that it's just an emergent property of our overall sexuality, which rests on a continuum. There is no "one right way" for everyone to have or enjoy sex, but instead a whole range of possibilites for the individual to practic and prefer. I've heard it suggested that a stronger sense of sexuality helped a group of organisms to out-reproduce groups with weaker senses of sexuality, and perhaps homosexuality is an emergent phenomenon of that hyper-sexualized libido. I don't know, but it's at least one way to explain how this could have evolved.

 

Another idea is that it has served social bonding purposes in pack animals. I tend to find this argument most compelling. The idea is that homosexual behavior increases group cohesion and descreases group tension. Obviously, more cohesive and well-functioning groups would outperform groups that are splintered and which have an "every man for himself" mentality.

 

For example, homosexuality could help the females garner favor with each other, and strengthen bonds like friendship, maybe increase the sharing of food and shelter, or care for offspring. Homosexuality could also help males to placate each other, especially dominant males who may kill the other male if his aggression is not checked somehow. Basically, the subordinate male accommodates the alpha male, hence strengthening the bond and saving his life. This obviously would have conferred benefit, as it often would have prevented the subordinate male from being killed. On top of that, though, the males woud also benefit in the same way as females, with greater/stronger friendships, more sharing of resources, and greater protection of family against attack and predation.

 

I briefly mentioned females, and to reinforce that point, you must consider just how important social bonding is for survival. The closer your bond with others in your group, the more help and protection you will receive. It is very likely that homosexual behavior allowed animals to avoid deep tensions and strengthen social ties with their sexuality. The group as a whole was stronger due to homosexuality strengthening bonds and decreasing tensions.

 

This behavior has been observed repeatedly in dolphins, for instance. Often when aggression stirs and danger is present for a dolphin, they will engage in a sexualized response and basically deflate that aggression by providing pleasure. Before long, the attackers and the attacked are frolicking through the water playfully... crisis averted.

 

Another theory mirrors the "grandmother hypothesis," in that homosexuals were hugely beneficial in caring for infant relatives, just like human grandmothers. Obviously, the more care an infant is given, the greater its chances of survival, ergo the homosexual behavior was selected for by the survival of the infant it helped raise. On top of that, the homosexual would not in a position to cuckhold the childs parent (to have that parent cheat on their partner with the person assisting in provision of care). The homosexual animal is a better care-taker in these respects, hence the benefit their offer is to the allele group of their tribe as opposed to their own individual set of genes. This is still a tentative hypothesis, but the idea that survival of the group can be more powerful than survival of individual is well accepted and easily explained.

 

There are some ideas off the top of my head. The biggest issue here (as I see it) is group cooperation, and how group survival was often more important than survival of one single member of that group, and that homosexuality conferred many advantages in that regard (ease of social tension, strengthening of social cohesion and bonds, dealing with survival in environments where mates were in short supply, assistance in child rearing, etc.). Then ultimately, those alleles got selected for since those groups tended to outperform groups with more rigid and puritanical sexual boundaries.

 

Also, I should note... There are over 1500 species which have been observed engaging in homosexual behavior. In fact, not one single species we've ever observed has been found NOT to engage in homosexuality. That seems to strengthen the premise of its biological nature. We discussed that some over in this other thread:

 

http://www.scienceforums.net/forum/showthread.php?t=36687

 

 

Good luck. I hope this has helped or at least steered you in the right direction.

[CDarwin]

Specific genes have actually been linked to homosexual behavior, too. If you muck with a gene called GB in a male fruit fly Drosophilia, for exmaple, it will begin attempting to mate with other males. Now of course humans are more sophisticated that fruit flies, so the matter is likely more complicated, but still the principle exists.

 

http://www.sciencedaily.com/releases/2007/12/071210094541.htm

 

I briefly mentioned females, and to reinforce that point, you must consider just how important social bonding is for survival. The closer your bond with others in your group, the more help and protection you will receive. It is very likely that homosexual behavior allowed animals to avoid deep tensions and strengthen social ties with their sexuality. The group as a whole was stronger due to homosexuality strengthening bonds and decreasing tensions.

 

That's precisely what bonobos, who are considered equidistant from us with chimpanzees, do, actually. Female-female sexual behavior (genital rubbing) among bonobos is actually more common than male-female sexual behavior, and is used to release tension at times of increased likelihood of conflict, such as at the discovery of a new food resource. Male-male sexual behavior also occurs at high frequencies as well.

 

It should be noted, however, that these females also mate with males when in estrous, so aren't as individuals true 'homosexuals.' That does seem to be more of a human thing, and tied up more heavily in the complexities of human culture and psychology than in simple biological drives.

 

For example, many homosexual men marry and father children, so obviously they are capable of physiological arousal in the presence of women, even if they have a psychological preference for males and may even find the experience traumatic. Likewise, otherwise 'heterosexual' males can often, in circumstances such as prison, respond sexually to other males. Indeed, in whole cultures, such as the Etoro, homosexual behavior is encouraged as a norm and almost all males engage in it. Surely this one culture isn't made up entirely of biological homosexuals. So, it seems to me sexuality is something of a gray area, to be nudged in one direction or another by rather complex assemblages genetic, psychological, and cultural factors.

[mooeypoo]

@ iNOW

In biology, we learn that the "survival of the fittest" depends on how many offsprings they can pass on their genes too.

That's a bit simplistic. We can go with that, but I just feel the need to point out that it's not quite just that.

 

Homosexuals can't pass there genes to anyone, and thus that provides a large hurdle in any gene theory of homosexuals but then again there are numerous genetic possibilities that would allow for homosexuality.

First off, that's not true. Not anymore, anyways. There are many homosexual families that are bearing children - their *own* children. A pair of women usually have more "luck" in "mixing" both of their genes by taking the egg of one woman and implanting it in the womb of the other. A pair of men might have to pick which of them is the biologic contributor, but that can - and is - done.

 

But I do get what you mean - these methods are only available recently (with technological advancement), which still doesn't explain how homosexuality "stayed" in society for so long.

 

However -- that brings me back to the first point, about the over-simplistic presentation as "survival of the fittest". We sometimes don't know what or why certain things develop, and the idea of marking them as "bad" or "good" is our own (limited) interpretation, and not really any natural 'intention'.

 

for example, I have glasses. Poor eyesight existed for a VERY long time. You'd think evolution by natural selection would get rid of it. And yet, here it is.

 

It might also be "resurfacing" because of changes in our recent habitat. If I take my glasses example, I was told by my eye doctor that if there were no computers in the world, I probably would have had no need for glasses at all. Changes in our environment recreated "flaws".

 

Not every development, and not every development that "sticks", has to do with *only* the continuation of the gene pool. The situation is much more complicated than that, and there isn't really much of a problem with homosexuality being developed in a society if you take those into account.

 

The fact that there is homosexuality in other animals can also suggest that, perhaps, it is beneficial for groups of animals (or humans) who are, relatively for their environment, over populated, to develop some parts of their group as homosexual tendencies. There might be an actual benefit in having them (like reducing the fight over females).

 

~moo

[Mokele]

A pair of women usually have more "luck" in "mixing" both of their genes by taking the egg of one woman and implanting it in the womb of the other.

 

A small, technical note - this would not result in any 'mixing' of genes - the egg would only contain the genetic material of the egg-mother and the sperm-donor, with no genetic influence from the womb-mother.

 

 

As to the broader topic, another point worth considering - maybe there *is* no selective advantage, either through kin selection or anything else. Maybe it's a spandrel, a by-product of other adaptations which simply occurs because of "the way things fit together" in the organism.

 

Mokele

[mooeypoo]

A small, technical note - this would not result in any 'mixing' of genes - the egg would only contain the genetic material of the egg-mother and the sperm-donor, with no genetic influence from the womb-mother.

 

 

As to the broader topic, another point worth considering - maybe there *is* no selective advantage, either through kin selection or anything else. Maybe it's a spandrel, a by-product of other adaptations which simply occurs because of "the way things fit together" in the organism.

 

Mokele

Hm, thanks for the clarification, that's interesting, I thought that there's still some contribution from the womb, so it's interesting to know otherwise.

[Xittenn]

I still don't understand why anybody would look for one specific gene that actually causes Homosexuality it's almost the least likely case.

 

http://www.acnp.org/g4/GN401000174/CH170.html

 

Not to compare Homosexuality to drug addiction but...................

 

"Candidate Genes

 

Knowledge about the cellular and molecular bases of acute drug action has exploded over the last several years. Information about the genes expressed by brain systems on which drugs act has allowed testing of the possibility that interindividual differences in genes encoding proteins expressed in these systems could contribute to interindividual differences in drug abuse vulnerability (reviewed in ref. 65).

 

Significant data now support the idea that virtually every abused drug can induce behavioral reinforcing properties by altering function in brain dopamine circuits arising from the ventral midbrain (16). Genes important in the mesolimbic/mesocortical dopaminergic pathways are thus strong candidate genes for possible contributions to interindividual differences in substance abuse vulnerability. The dopamine D2 receptor gene (see below) represents one such candidate gene.

 

Recent molecular cloning studies have also identified the genes encoding many drug receptors, including the dopamine transporter that is the pharmacologically defined cocaine receptor, G-protein-linked opiate receptors that are the heroin/morphine receptors, the G-protein-linked cannabinoid receptor that mediates marijuana action, the N-methyl-D-aspartate (NMDA)-glutamate receptor ligand-gated ion channels that mediate phencyclidine actions, the nicotinic acetylcholine receptor ligand-gated ion channel that is the site of action of nicotine, and the gamma-aminobutyric acid (GABA) receptor ligand-gated ion channels that mediate actions of barbiturates and benzodiazepines (see ref. 33 for review). GABA and NMDA receptors are also strong candidate loci for acute ethanol effects."

 

 

It would seem to me that it should be looked at from a broader less direct implication.........Because there are so many different reasons why individuals indentify within this/these groups!

Edited February 19, 2009 by buttacup