People's sexual attractions are clearly biological, so thus orientation is as well. How anyone can argue against this is beyond any sense of logic. Sexual orientation has a biological basis, and people just need to learn to love with this fact. It's time to stop being a bigot and accept reality.
Canadian Scientist (who discovered the hypothesis) Anthony Bogeart studied over 1000 men, including men that have been adopted or brought up with step-siblings. In his findings, the mother's age, having sisters or step-siblings had no effect on sexual orientation. However, interestingly enough, blood-brothers that were raised separately did. This shows there is some biological basis for this principle.
I should start by saying I am a pro-gay bisexual.
But I am concerned about the discourse surrounding sexual orientation and whether or not it is a choice. I fear that it is distorting thinking about genetics in general.
It's NOT all or nothing. Showing there are biological factors that contribute does not show that choice plays no role whatsoever. There are no studies that show a 100% correlation with biology. Yet people speak about studies showing partial correlations as if they did. This could lead people to hear about for instance genetic correlations with religiosity and then assume that religion is not a choice either, rather than that genetic factors influence a tendency (NOT an inevitability, a tendency. Tendencies are not inevitabilities.).
One very poor argument is "why would somebody choose?" Why in spite of persecution did people keep converting to Judaism (including during the 1930s in Nazi Germany believe it or not)? That doesn't mean Judaism is not a choice.
And the dreaded "when did you choose?" creates a dichotomizing conceptualization of "choice". Choice is NOT black-and-white. It doesn't have to mean a deliberate, conscious choice is made every single time or even that when one is made that it becomes effective immediately without any mental effort or long-term patience.
I didn't choose not to like mushrooms, AT FIRST. Then over a period of time which I think not so coincidentally I was just generally shifting towards healthier eating habits and knew that mushrooms were nutritious and even thinking to myself that I wanted to like them in order to experience the power of neuroplasticity I grew to like them. During that time there were quite a few times when I tried eating them and didn't like them, but eventually I did. It didn't happen over night and I can't pinpoint a specific time when I "converted".
Why do I think sexual orientation is a choice? Neuroplasticity. Mounting evidence shows that we have great power to rewiring our own brains. And as I read more about neuroplasticity the more I tried to do that to myself and it's worked. I was once inattentive and messy, I am becoming more disciplined and focused. I loved junk food, now I love healthy food. Granted I didn't try to change my sexual orientation. I don't see a point. Being bisexual I don't have to worry about Mr. Or Mrs. Right not being the right gender. I choose my partners on personality, intelligence, and interests, which I believe is the best way to choose a partner and if I knew someone was just perfect for these factors but there was some off-putting physical trait I'd try to cultivate it as an "acquired taste" much like I did for mushrooms.
Although genetics play a role in determining sexual orientation, it is not the final piece of information necessary to determine one's sexual preferences. Fraternal birth order has nothing to do with sexual orientation altogether. People are born with the capacity to love anyone. It is the indoctrination during childhood and beyond by parents, teachers and society at large that places limitations on sexuality.