If being gay is in your DNA...then why aren't all sets of identical twins in which BOTH are gay? Identical twins essentially have the same DNA...and yet studies vary widely when it comes to finding sets of twins where both are gay. Percentages range from 10-50%...and usually have a particular bias from the outset. Still...common sense would say that if twins share nearly identical DNA...and a large percentage of them are NOT both gay...then other factors...environmental, social, psychological or choice must be involved.
A far better argument against it being tied to DNA is the inherent suicidal aspect of the trait. Homosexuality leads to a fairly obvious problem when it comes to reproducing, thus the gene should inevitably be spread thin or vanish from the gene pool.
I should however point out a few other things.
First, biological causes does not necessarily equal DNA. Genes are one factor, but any number of abnormalities can be present in an individual without there being a genetic reason for them. Mutation, injuries and environment all have an impact on your development and biological state. I remember one study that concluded that there were distinct similarities between a homosexual man and heterosexual woman in an area of the brain that deals with sexuality (all I remember of the actual study was that they cut the brains into thin slices and saw the structure/number of some kind of pathways).
Second, based on studies of sexuality in primates, bisexuality is apparently fairly common. As animals are generally not influenced by social factors in the way or extent that humans are, this would indicate that there's at least some biological basis for it. Plus, bisexuality in social animals (thus also humans) makes perfect sense from an evolutionary point of view. Homosexuality doesn't, as I pointed out, but this may simply be an extreme manifestation of the same trait.
To use an analogy, it may very well be that biology dictates the hand we're dealt, but social factors decide how we play it. If this is so, biology could certainly be blamed in the cases of someone being dealt a particularly, erm, gay hand.
Let's get one thing straight: When you are born, you don't know what sex is. When you are born, you don't know what relationships are. When you are born, you don't know what a kiss is. When you are born, you don't know what spaghetti is. When you are born, you don't know how to ride a bike. When you are born, you don't even know who or what you are. When you are born, you don't know anything.
That's not entirely true. Reproduction is a basic instinct. Even plants are aware of the basics. They may not
understand it, but that is another matter. Animals don't need to be told who to have sex with or how to do it, they seem to be fairly good at figuring it out on their own.
Here is a serious question for those people who claim that being gay doesn't involve any sort of personal choice (and I'm dead serious)...
If you are truly "born" with a certain sexuality, making you sexually attracted towards different things, then what about pedophiles or people who are into beastiality?
If people are "born" with a certain sexuality, then it's not their fault that they are sexually attracted to those things, yet, I'm sure that 99.99% of people who claim that they are "born" a certain way will never defend such actions. Why not? Maybe they don't choose to be that way.
The same logic is used when questioning personal responsibility and destiny. The generic question is: if I am ruled by an external factor of which I have no control, what gives you the right to punish me? The generic answer: if you are ruled by an external factor that forces you to act in a certain way, then I too am ruled by an external factor that forces me to punish you for it.
At any rate, as I've pointed out before, I doubt it's as simple as either something you are, or something you actively chose. There's a whole range of possibilities in between.
