Could be an interesting topic of discussion, the evolutionary advantage of homosexuality.
Yep, there's already been threads about it, including
Homosexuality and Genetics, which you can check out and resurrect if you have anything to add.
I would think there is a sound biological reason for it.
One hypothesis is that a genetic makeup that results in homosexual males also results in hyper-fertile heterosexual females, who in addition to having more progeny, may have homosexual male family members to help insure her progeny's success. A reference can be found in the thread
Gay gene increases female fertility.