Gays in Iran?

The audience spontaneously laughed when Iranian President Mahmoud Ahmadenijad said there are no homosexuals in Iran.  They were mostly students at  Columbia University and the Iranian president was responding to this question submitted by one of them: 

Why does the Iranian government execute homosexuals?

Ahmadenijad responded,

In Iran, we don't have homosexuals like in your country.

But when everyone laughed, he reacted defensively...

We don't have that in our country.

In Iran, we do not have this phenomenon.  

I don't know who's told you that we have it.

The question I ask is why did the audience laugh in the first place?

We can be fairly sure that they laughed because that first statement contradicted what they believed to be an obvious truth.  Ahmadenijad's avoidance of a direct answer might have drawn snickers, but not the loud laughter that ensued.

There is no escaping the fact that most of the audience assumed there really are homosexuals in Iran; and if we are honest with ourselves, most readers probably assume that somewhere between 2-5% of any large population would tend toward homosexual identities if they had the freedom of expression to do so.  We have basically learned that from social science research.  And we also know that homosexual behavior has persisted throughout history.

What gets me is why some people argue that homosexuality is strictly a learned behavior. We see so many other areas in which the physical creation has been marred by human sinfulness, yet somehow we seem to think that this aspect of the human genome is protected. There are inherited diseases; and, theologically, we attribute these to the effects of sin.  We know that genetics does have an influence on behavioral matters; but for some reason many seem resistant in principle to any suggestion that there may be a physical component to homosexuality.   Yet it seems likely that there must be a genetic basis if this behavior can be so universally expected.  It seems that even our sense of humor bears witness to this probability.