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Homosexuality as an adaptive trait?
Topic Started: Mar 19 2009, 10:49 AM (1,671 Views)
Giant Blue Anteater
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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.
It is not a mental illness. It is just a preference of the same sex, nothing more, nothing less.

And it does actually have to do with evolution, at least, it helped it in social animals. Read the quote from Neil Gostling.
Edited by Giant Blue Anteater, Mar 19 2009, 07:06 PM.
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Genesis
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I simply mean that I don't believe that it has any relation to beneficial adaptation, at least in humans. I'm sorry if I said this in an offensive way, but I couldn't think how else to put it. I don't see it as anything more than a mutation that could, perhaps, occur by the slightest shift in a single genome, during birth.

I won't claim that I don't find it offensive when someone uses the word 'gay' (which, in my own community, at least, tends to be used as a general, meaningless offensive term) to insult me, but I am not homophobic. Though perhaps understated, homosexuality, the way I see it, is a mutation that should be no more controversial than being double-jointed or being able to turn one's tongue upside-down in their mouth (both of which apply to me).
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ashwinder
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But then why is it so prevalent? Homosexuality results in a huge decrease in the number of offspring (around a 10 fold reduction in reproductively) which would make it, in evolutionary terms, quite a disadvantage. Yet rather than being actively selected against it occurs more frequently than all over genetic diseases put together. What I mean is being double-jointed or rolling your tongue does not effect fecundity like homosexuality does.

P.s. I understand you meant no offence and I apologise if I may have come across as harsh but the comparison between homosexuality and a mental disorder is frequently made by those with a real homophobic agenda.
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lamna
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What I mean is being double-jointed or rolling your tongue does not effect fecundity like homosexuality does.


Indeed, quite the opposite effect with those. *wink*
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ashwinder
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Haha, I walked right into that one!
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Viergacht
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Not every aspect of the human personality is directly adaptive . . . it bothers me that we're so desperate to justify the existence that we buy into these just-so stories without any solid evidence. That can be just as offensive. It doesn't need to be justified to anyone, imo.
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Flisch
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It's not about justifying this phenomenon. It's about understanding it. Once we know why it is still inherent in humanity, we might get a better idea of evolution in general. (Also the human is , by nature, curious. :P)
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ashwinder
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Viergacht
Mar 20 2009, 02:21 PM
Not every aspect of the human personality is directly adaptive . . . it bothers me that we're so desperate to justify the existence that we buy into these just-so stories without any solid evidence. That can be just as offensive. It doesn't need to be justified to anyone, imo.
To an extent I do agree, some theories are so unfounded that they might as well be just-so-stories. But I think when a behaviour poses an evolutionary conundrum (like homosexuality) we shouldn't just go 'well that's just a funny human quirk' and leave it be. I believe that as part of the animal kingdom our evolution obeys the same laws as any other species. The argument I put forward, about it being a form of alliance formation between all-male bands does actually have a few studies which whilst not 'solid' as such are at least interesting enough to explored further.
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Viergacht
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Yeah, I just don't find it terribly interesting, I guess.
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Paralith
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Neil Gostling's explanation is interesting but not entirely accurate. Homosexual behavior is rampant in primates, especially the great apes, but what is unique to humans is exclusive homosexuality, being actually repulsed by the opposite sex. In all primates the individuals who at times behave homosexually still attempt to get heterosexual matings just like all the rest. Male gorillas, for example, when not big or strong enough to gather a harem of their own, live in multimale groups where they all engage homosexually with each other. But when the opportunity arises to get their own harem of females, they will fight the others for it. Female bonobos cement social relationships with sexual intercourse with both sexes, yet when they're ovulating they still seek out a male.

Obviously human sexuality covers a broad continuum, but we are still unique in having individuals who are solely interested in the same sex. And Viergacht, homosexuality is also interesting because there are different forms of it present in wide varieties of cultures all across the planet. When a trait is common in many humans in differing environments and differing ethnic backgrounds, then it is more likely to be a result of our common descent, and at least partially determined by genes, then it is to be a mere coincidence. And as ashwinder has said, the fact that it is so prevalent (I myself have heard estimates as high as 7 - 10% of the population, and that's HUGE! That means out of 300 million total people in the US, up to as many ass 3 million could be homosexual if these estimates are correct) and so detrimental to direct reproductive success strongly suggests that it is either adaptive in an indirect way or some of the genes that affect it are adaptive in other ways. Most complex behaviors are the result of multiple genes, and many of those genes can also affect other traits besides the one in question. If one of those traits are HIGHLY adaptive, they may have dragged along homosexuality as a side effect. (This also implies that human homosexuality is a relatively recently emerged trait; after long periods of time, traits with a similar beneficial result but lacking the reproductively detrimental side effect will be selected in favor of the traits with the detrimental side effect.)

I also think it's likely that homosexuality is the type of trait where many people may exhibit the same outward phenotype, but the developmental and/or genetic pathway that lead them there can be very different. Some genetics studies suggest that male and female homosexuality have different causal architectures, and others suggest that homosexuality in some males is affected by genes at a certain area of the x chromosome, while homosexuality in other males may be affected by genes at a different chromosome instead. It's a very complicated issue and the story may not be the same for all people who self-identify as homosexual.

PS - culture does not negate evolution. Evolution is nothing but genetic change, and studies have shown that humans have exhibited a great deal of genetic change at the very least into our recent past, and probably continuing today. You are probably thinking that culture negates natural selection, but that's not necessarily true either. Natural selection only means that those individuals who function best in their particular environment have the most reproductive success. Culture has changed our environment significantly, but it's still an environment, and not everybody has the same number of children. Some of us do better than others in that respect, and that's natural selection at work.
Edited by Paralith, Mar 21 2009, 04:18 AM.
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