Unsilenced said:
Sexuality's a spectrum, imo, so people who like men more then women while still liking women would have no problem having kids. There's also a desire for children that is removed from sexual feeling. When you couple that with societal pressure toward heterosexuality throughout history, it's not unlikely that gay men or at least gay leaning men would spread their genes. Of course, there's always the possibility of random mutation causing both nonsexuality and homosexuality, but this is far more unlikely to occur on a level that lends about 7% of people a certain sexuality as homosexuality does. In fact, it's the only statistically relevant way for genetic nonsexuals to occur short of nonsexual women being raped.
In short,
Gay gene: Rape, Bisexuals passing genes down, random mutation, cultural pressure
Nonsexual gene: Rape, random mutation (A true nonsexual man would not be able to give in to cultural pressure due to inability to get aroused, nonsexual woman could theoretically, but the conditions would be similar to rape, it's a gray area)
Gays are still more likely to occur.
Edit; Also, homosexuality as a mutation simply requires a change in the target of desire, nonsexuality as a mutation requires a far greater change in one or all of the parts of the human reproductive and hormonal systems. Also, as you claim to be nonsexual, can you actually gety an erection, climax, or feel sexual desire? Or have you just never wanted to or felt like having sex? There is a difference.