I just want to emphasize (since I’m sure you are aware of this fact) that all this means is that there is not a single “gay gene,” and not that genes cannot affect orientation in a complex way.
One moderately famous example: The Krays. (You know, Doug and Dinsdale.)
There are lots of cases where one identical twin is left-handed and the other isn’t, by some studies far moreso than cases of gay Id.twin/straight Id.twin, and yet “there is evidence that handedness is hereditary and that [the neurological causes of a particular handedness*]are present from birth”. Few believe that left-handedness is a choice or has no bio-component.
*[bracketed portion] is mine- synopsizing what wouldn’t make much sense out of the context out of the article
BTW, an argument that hasn’t come up here but one that I’ve heard repeatedly and actually had to address today is the issue of “How can it be hereditary or genetic if gays don’t have kids?” While most Dopers can figure that one out, for the benefit of 18 year olds who are new to the apologetics and the like, please remember that there was no such thing as “gay” until recently. There has always been homosexuality, of course, but most same-sex oriented men and women hid it and many (if not most) married and had kids- and if only 10% of all [what we would now call] gays married and had kids in any generation [and more than that marry and have kids today), then over time that’s still enough to spread the genes everywhere. Every one of us is probably a descendant of someone who was naturally same-sex oriented within just the past few generations, so that would have definitely put the genes in the water.
As for how it could benefit humans to have gay genes (and yes, it’s certainly not proven there’s a genetic sequence), there are many theories. E.O. Wilson’s The Good Uncle Theory is one that has several variants- that a subset of humans from whom large percentages voluntarily remain childless benefits society for several reasons.
Yeah, but that doesn’t really prove anything one way or the other, as most identical twins, aside from sharing the same genes, also will share the same upbringing.
To elaborate on this since I am expressing myself somewhat poorly here–as Sampiro notes traits can have a genetic basis but not show up 100% of the time in identical twins. This is because there are many other factors that affect the expression of these traits, both pre- and post-natally. This is why twin studies often use a measure called the monozygotic : dizygotic ratio to determine the strength of genetic influences.
Plus twins-raised apart studies, though for obvious reasons they’re reasonably rare.
One explanation I’ve heard is that in hunting and gathering days homosexuality may have allowed a tribe to reduce internal conflict caused by competition for females while still allowing the tribe to keep enough males around to defend the tribe’s territory.
That’s the wonder of neo-Darwinism. With a little imagination, you can explain almost anything with it.
Personally I think it’s more akin to the same reason some people have perfect pitch and others can’t carry a tune, or some people have artistic ability and others don’t. Like Pooh, it just is.
Gay sex is one thing, but let’s keep poo out of this discussion.
I wonder if “Does Winnie the Pooh shit in the Hundred Acre Woods?” was how they started calling it ‘poo’.
Biology is not destiny, nor is behavior entirely fixed at conception.
Heredity, societal? Maybe in some cases it’s just personal.
Tris
Homosexuality is caused by the same things that causes heterosexuality. We have some intriguing clues from things like twin studies, but we don’t really know yet. The current answer looks like it’s a fairly even mix of biology and psychology. I don’t think it’s really a choice to have certain desires, although of course it’s a choice to a certain extant of how you act on those desires. In general I think it’s better to avoid acting on desires that are destructive and to promote acting on desires that are fulfilling. Whether you consider homosexual behavior ultimately fulfilling or destructive I would say is up to you. I don’t think that that other people’s prejudicial discomfort of homosexuality should be factored in as a legitimately destructive element. As long as it’s consensual, and doesn’t harm you or the other person, I think exploring any sexual desire is fufilling.