Fascinating! To me this sounds like the mother's body is trying to "nudge" the odds towards a daughter after several sons, but sometimes the process "fails" and produces an effeminate male instead - a gay son. Alternatively, some kind of meta-level mechanism to reduce competition over women in the community, ultimately improving its collective health and well-being.
> gay son
This is a dangerous stereotype that is equally harmful to people of any sexuality, I'd encourage you to correct it. Most of the gay folk I know personally tend towards the athletic end of the spectrum