Social pressures in many cultures, such as taboos created by law or religion, have kept homosexuals from openly being in homosexual relationships. Such pressures encourage them to take heterosexual spouses, bear children, and so on, despite their natural orientation. Within the last few generations, we've witnessed a gradual shifting to allowing men and women to engage in homosexual relationships.
That said, if the "gay gene" exists, it is my theory that one of the strongest sustaining forces for it may have been the anti-homosexual taboos of the past. Following this line of thought brings one to an unpleasant conclusion; as the taboos of the past are lifted, fewer homosexuals will be under social pressure to engage in heterosexual relationships. As such, fewer homosexuals may directly pass on their genes, leading to a diminished gay population.
Of course, this doesn't mean that all homosexuals will immediately stop having children. I have even known gay couples who discussed having close friends surrogate for them, so they could both have biological children... and who knows what possibilities may open up in the future. Still, if homosexuality is indeed purely genetic, it makes me wonder how recent social changes might impact this.
On a fairly unrelated note: education is key to resolving many social issues.
Here's a petition to help further education in impoverished areas, by guaranteeing access to school libraries for all students. It's a small something, but something you can do to help schools and their students ensure more equal access to education for everyone, regardless of their means.