Let’s start with some visual evidence:
Here are Roy and Silo, the most famous gay penguins.
Homosexuality is well documented in penguins and other animals.
Do oysters make a choice?
While not saying that an oyster is gay, they do change gender once or more times during their lifetime. (And, as an aside, as the article asks, how hungry did someone have to be to eat the first oyster?)
Back to the subject. The oysters aren't gay, but they are an example of the sexual diversity that exists among the animal kingdom.
Reproductive diversity in the animal kingdom is present in seahorses as well. Again while not addressing sexuality, the fact that the male gives birth reminds us that among animals, fish in this case, things are not so simple. Watch the male having babies.
Let's see. Same sex behaviour is observed in over 1500 animal species. I won't post a video of every species, but this video contains images from a documentary, "Out In Nature: Homosexual Behaviour in the Animal Kingdom".
Now lets move to human research. Here is the first sentence and the last sentence of an article published in the Proceedings of the National Academy of Sciences of the United States of America, by Dick Swaab (PNAS July 29, 2008 vol. 105 no. 30 10273-10274).
Current evidence indicates that sexual differentiation of the human brain occurs during fetal and neonatal development and programs our gender identity—our feeling of being male or female and our sexual orientation as hetero-, homo-, or bisexual.
Neurobiological research related to sexual orientation in humans is only just gathering momentum, but the evidence already shows that humans have a vast array of brain differences, not only in relation to gender, but also in relation to sexual orientation.
This is but one paper from recent research that explores human sexuality from a scientific standpoint. The paper (as most scientific papers do) asserts that more research is needed, and of course, this is happening.
I only wanted to give an example showing there is evidence, contrary to what the commenter said, that sexual orientation is not a choice.
Non-human animals don't really have the option of choosing. Or do they? If you say yes, then that gives them a quality that once was reserved for humans. It makes us just a little more close to the rest of the animal kingdom than some Christian conservatives would like. But if they don't have a choice, then it must be science that is making them behave in the ways they do.
I could go on and on about science, but that is enough for now.
Research is in our favor. Science is in our favor.