Here's one idea of how this might coincide. If it seems far-fetched, then hey, it's just an idea. :)
There's some evidence in
this this Nature article that suggests that the more older brothers a male has, the more likely he is to be homosexual. If this is true, then homosexuality genes, originally created through genetic drift, could still be passed on by heterosexual siblings.
It does sound pretty far-fetched, but is a neat idea!
That same article also says that you can tell whether or not someone is a lesbian by the relative lengths of their index and ring fingers. I know, it sounds like total BS, but apparently there's some evidence for it.