Homosexuality
I think people's masculinity and feminity are on a sliding scale.
If a boy is born with a 40% masculine and 60% feminine he will have a soft voice and act more girly than a boy born 70% 30%. Then I think environment kicks in.
Look at all the butch lesbians......they are women but they look rugged and manly.
I think nature has a huge part in it, but people will often conform due to their society's standards.
This is all a theory I came up with. Alot of gay guys end up being models due to them being closer to a woman genetically.