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Homosexuality as an adaptive trait?
Topic Started: Mar 19 2009, 10:49 AM (1,672 Views)
ashwinder
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As an evolutionary psychologist I believe that many human traits and behaviours can be attributed to evolutionary causes. I have written a few papers on the subject of homosexuality and how and why it might fit with Darwinian explanations.

The basic premise is that homosexual behaviour exists throughout the animal kingdom. In humans at least, it is heritable and shows a strong genetic relationship... yet it results in a significant reduction in future offspring and therefore reproductive fitness. The argument therefore goes that homosexuality must offer some other advantage in terms of fitness to allow it to remain in the gene-pool at such a high rate.

So what do you think? Could homosexuality be an advantage is certain situations? How might homosexual interactions have evolved and be maintained within populations?
(I'll add my own thoughts later)
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Viergacht
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Last theory I heard was that it was a byproduct of something that caused higher fertility in sibling females. It's difficult to sort these things out with humans because culture negates evolution - for example, having post-menopausal females living long lives. The theory is that they're contributing wisdom and childcare, but that's something in the nature of a just-so story, and they're not passing anything on genetically so it doesn't affect evolution.
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Carlos
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Homosexuality evolved in human beings as a reproductive strategy; most homosexual males are the younger brothers of a family (expections don't count), and so, rather than competing with their brothers, they originally simply stayed to take care of younger family members (little brothers or the offspring of their sibilings). I don't know about lesbianism though.

This strategy does parallel that of certain birds like ground hornbills and passerines
Edited by Carlos, Mar 19 2009, 11:26 AM.
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ashwinder
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Quote:
 
Having post-menopausal females living long lives. The theory is that they're contributing wisdom and childcare, but that's something in the nature of a just-so story, and they're not passing anything on genetically so it doesn't affect evolution.

Well it does if they're helping their daughters raise children, they would therefore be increasing their inclusive fitness and their post-menopausal genes would be passed on to future generations.

Quote:
 
Last theory I heard was that it was a byproduct of something that caused higher fertility in sibling females.

Some say that if homosexuality was carried like sickle-cell anemia (on two alleles) then those sons with one would have an advantage where as those with both would be gay. I just wish there was more information on what this advantage which converts into high-fertility would be. Some have hypothesised increased promiscuity but then I think that comes from a lack of understanding of the gay community and overplaying of stereotypes!

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Homosexuality evolved in human beings as a reproductive strategy; most homosexual males are the younger brothers of a family (expections don't count), and so, rather than competing with their brothers, they originally simply stayed to take care of younger family members (little brothers or the offspring of their sibilings).

This one is interesting but still a bit shaky... firstly in eusocial species where there are nonreproductive helpers these helpers do not engage in sex of any kind. Why not just have sterile helpers rather than helpers who waste time that should be spent helping siblings on having homosexual relationships? Studies have also shown that gay-men tend to help their siblings less than straight siblings so if they were analogous to a worker caste then they'd be a pretty rubbish one.

Personally I believe that homosexuality, in primates at least, evolved as a form of alliance formation. Male alliances are important in many primates and bonobo and gorilla males might arguably be using homosexual interactions as social currency. I believe that those predisposed to some homosexual activity, those that are more sexually plastic, benefit over those who are entirely straight. Us homosexuals are merely a byproduct of such an equation!

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Carlos
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Really? Oh well, I really wanted to be the human answer to a hornbill :(
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ashwinder
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Indeed, but the idea of being the human equivalent of a insect worker-caste would be a bit rubbish... it'd mean my sister would have some evolutionary right to get me to help her raise whatever illegitimate devil spawn she finally decided to pop out!
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Giant Blue Anteater
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Homosexuality, actually does help, although their genes (if a homosexual gene exists) will not be passed, they will help their siblings pass on their genes.

From Neil Gostling at Ask a Biologist:
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...there is a good reason for homosexuality in animals. Certainly, the genes of a specific homosexual animal are unlikely to be passed on, but in primate populations the presence of homosexual males may allow familial DNA to be passed on.
What I mean is this. If an individual (non-homosexual) is in a family group with other males (this is quite common with species of monkey) he shares much of his DNA with his brothers, which may have a high frequency of homosexual individuals. By having homosexual males in the group he does not compete with them to mate with the females also in the group. The advantage of this is that the males can 'defend' the clan. The actual homosexual individuals 'never' pass on the genes, but they increase the odds that their brothers genes (many of which they have because they are related) are passed on by defending the females from unrelated males.

In this scenario, homosexuality allows familial (related) genes to be passed on, even if the homosexual individual's genes are not.
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Genesis
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....It's a relatively uncommon mental illness... I dout it has anything to do with evolution. Besides that, evolution cannot occur in humanity unless a secluded population inbred. (The reason cultures cut-off from mass society tend to have more noteworthy physical traits, such as pygmies in some locations.) However, we are mentally devolving, with every generation.
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Carlos
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If it is a random mental disorder then why is it present in pratically all tetrapods?
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lamna
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Mental disorder? Hmm, that's rather rude and I don't think it is accurate. However it could be present in many animals. Albinism is present in many animals.
I have avoided posting heir because I know bugger all about it, other than some vaguely remembered fact that it might have something to do with hormones and pregnancy.

Devolving is not a correct term. Everything is just evolution. A ostrich is not a devolved bird any more than a less intelligent human is a devolved one.
Besides we are not getting stupider. We are getting more intelligent thanks to better nutrition and education, though we have the same potential as someone from 10,000 years ago.
Just because stupidity is more visible now (Decline of Classes and the internet are big factors in this.) does not mean mankind is becoming less intelligent.
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Are nipples or genitals necessary, lamna?
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ashwinder
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Genesis
Mar 19 2009, 06:14 PM
....It's a relatively uncommon mental illness... I dout it has anything to do with evolution. Besides that, evolution cannot occur in humanity unless a secluded population inbred. (The reason cultures cut-off from mass society tend to have more noteworthy physical traits, such as pygmies in some locations.) However, we are mentally devolving, with every generation.
Uh ok that's extremely offensive. Mental disorder?!! *checks calendar* phew I thought we'd warped back to the 50's for a second!

Also rare? Uh nope, 1-4% of the population isn't really rare, it's more common than any known genetic disorder and over 6 times more common than say schizophrenia. Think before you post next time.
Edited by ashwinder, Mar 19 2009, 06:39 PM.
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Carlos
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Genesis was the one that stated it was an unusual mental condition. I just used "disorder" rather than "illness", because it causes a shock effect. Anyway, I don't think I'm mentally retarded or something; my sexuality isn't caused by a malfunction on the brain
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ashwinder
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I wasn't offended by your comment Johnfaa as I could see it was a retort. To be honest I'm not even particularly offended by Genesis either I just think it shows surprising small-mindedness.
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lamna
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Well that is what we are trying to figure out on this topic. If it does not have a function then their is something "wrong" with JohnFaa's brain, and mine too. Of course it's harmless apart from the fact it makes it a little harder to breed.

If it has a function then it is not a disorder but rather a adaptation.
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Are nipples or genitals necessary, lamna?
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ashwinder
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Well I wouldn't worry, the evidence appears to show that homosexuality wouldn't exist to the extant it does if it was a true 'disorder'. Homosexuality or at least bisexuality is actually the norm in most vertebrates it's pure-heterosexuality that is 'deviant'! :)
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